.\" $MirOS: src/bin/mksh/mksh.1,v 1.388 2016/01/20 22:04:54 tg Exp $
.\" $OpenBSD: ksh.1,v 1.160 2015/07/04 13:27:04 feinerer Exp $
.\"-
.\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
.\"		2010, 2011, 2012, 2013, 2014, 2015, 2016
.\"	mirabilos <m@mirbsd.org>
.\"
.\" Provided that these terms and disclaimer and all copyright notices
.\" are retained or reproduced in an accompanying document, permission
.\" is granted to deal in this work without restriction, including un‐
.\" limited rights to use, publicly perform, distribute, sell, modify,
.\" merge, give away, or sublicence.
.\"
.\" This work is provided “AS IS” and WITHOUT WARRANTY of any kind, to
.\" the utmost extent permitted by applicable law, neither express nor
.\" implied; without malicious intent or gross negligence. In no event
.\" may a licensor, author or contributor be held liable for indirect,
.\" direct, other damage, loss, or other issues arising in any way out
.\" of dealing in the work, even if advised of the possibility of such
.\" damage or existence of a defect, except proven that it results out
.\" of said person’s immediate fault when using the work as intended.
.\"-
.\" Try to make GNU groff and AT&T nroff more compatible
.\" * ` generates ‘ in gnroff, so use \`
.\" * ' generates ’ in gnroff, \' generates ´, so use \*(aq
.\" * - generates ‐ in gnroff, \- generates −, so .tr it to -
.\"   thus use - for hyphens and \- for minus signs and option dashes
.\" * ~ is size-reduced and placed atop in groff, so use \*(TI
.\" * ^ is size-reduced and placed atop in groff, so use \*(ha
.\" * \(en does not work in nroff, so use \*(en
.\" * <>| are problematic, so redefine and use \*(Lt\*(Gt\*(Ba
.\" Also make sure to use \& especially with two-letter words.
.\" The section after the "doc" macropackage has been loaded contains
.\" additional code to convene between the UCB mdoc macropackage (and
.\" its variant as BSD mdoc in groff) and the GNU mdoc macropackage.
.\"
.ie \n(.g \{\
.	if \*[.T]ascii .tr \-\N'45'
.	if \*[.T]latin1 .tr \-\N'45'
.	if \*[.T]utf8 .tr \-\N'45'
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.	ds sR \(aq
.	if \*[.T]utf8 .ds sL `
.	if \*[.T]ps .ds sL `
.	if \*[.T]utf8 .ds sR '
.	if \*[.T]ps .ds sR '
.	ds aq \(aq
.	ds TI \(ti
.	ds ha \(ha
.	ds en \(en
.\}
.el \{\
.	ds aq '
.	ds TI ~
.	ds ha ^
.	ds en \(em
.\}
.\"
.\" Implement .Dd with the Mdocdate RCS keyword
.\"
.rn Dd xD
.de Dd
.ie \\$1$Mdocdate: \{\
.	xD \\$2 \\$3, \\$4
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.el .xD \\$1 \\$2 \\$3 \\$4 \\$5 \\$6 \\$7 \\$8
..
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.\" .Dd must come before definition of .Mx, because when called
.\" with -mandoc, it might implement .Mx itself, but we want to
.\" use our own definition. And .Dd must come *first*, always.
.\"
.Dd $Mdocdate: January 20 2016 $
.\"
.\" Check which macro package we use, and do other -mdoc setup.
.\"
.ie \n(.g \{\
.	if \*[.T]utf8 .tr \[la]\*(Lt
.	if \*[.T]utf8 .tr \[ra]\*(Gt
.	ie d volume-ds-1 .ds tT gnu
.	el .ds tT bsd
.\}
.el .ds tT ucb
.\"
.\" Implement .Mx (MirBSD)
.\"
.ie "\*(tT"gnu" \{\
.	eo
.	de Mx
.	nr curr-font \n[.f]
.	nr curr-size \n[.ps]
.	ds str-Mx \f[\n[curr-font]]\s[\n[curr-size]u]
.	ds str-Mx1 \*[Tn-font-size]\%MirOS\*[str-Mx]
.	if !\n[arg-limit] \
.	if \n[.$] \{\
.	ds macro-name Mx
.	parse-args \$@
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.	nr arg-ptr +1
.	ie (\n[type\n[arg-ptr]] == 2) \
.	as str-Mx1 \~\*[arg\n[arg-ptr]]
.	el \
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.	ds arg\n[arg-ptr] "\*[str-Mx1]
.	nr type\n[arg-ptr] 2
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.	nr num-args (\n[arg-limit] - \n[arg-ptr])
.	nr arg-limit \n[arg-ptr]
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..
.\}
.\"-
.Dt MKSH 1
.Os MirBSD
.Sh NAME
.Nm mksh ,
.Nm sh
.Nd MirBSD Korn shell
.Sh SYNOPSIS
.Nm
.Bk -words
.Op Fl +abCefhiklmnprUuvXx
.Oo
.Fl T Oo Ar \&! Oc Ns Ar tty
\*(Ba
.Ar \&\-
.Oc
.Op Fl +o Ar option
.Oo
.Fl c Ar string \*(Ba
.Fl s \*(Ba
.Ar file
.Op Ar argument ...
.Oc
.Ek
.Nm builtin-name
.Op Ar argument ...
.Sh DESCRIPTION
.Nm
is a command interpreter intended for both interactive and shell
script use.
Its command language is a superset of the
.Xr sh C
shell language and largely compatible to the original Korn shell.
At times, this manual page may give scripting advice; while it
sometimes does take portable shell scripting or various standards
into account all information is first and foremost presented with
.Nm
in mind and should be taken as such.
.Ss I'm an Android user, so what's mksh?
.Nm mksh
is a
.Ux
shell / command interpreter, similar to
.Nm COMMAND.COM
or
.Nm CMD.EXE ,
which has been included with
.Tn Android Open Source Project
for a while now.
Basically, it's a program that runs in a terminal (console window),
takes user input and runs commands or scripts, which it can also
be asked to do by other programs, even in the background.
Any privilege pop-ups you might be encountering are thus not
.Nm mksh
issues but questions by some other program utilising it.
.Ss Invocation
Most builtins can be called directly, for example if a link points from its
name to the shell; not all make sense, have been tested or work at all though.
.Pp
The options are as follows:
.Bl -tag -width XcXstring
.It Fl c Ar string
.Nm
will execute the command(s) contained in
.Ar string .
.It Fl i
Interactive shell.
A shell that reads commands from standard input is
.Dq interactive
if this
option is used or if both standard input and standard error are attached
to a
.Xr tty 4 .
An interactive shell has job control enabled, ignores the
.Dv SIGINT ,
.Dv SIGQUIT ,
and
.Dv SIGTERM
signals, and prints prompts before reading input (see the
.Ev PS1
and
.Ev PS2
parameters).
It also processes the
.Ev ENV
parameter or the
.Pa mkshrc
file (see below).
For non-interactive shells, the
.Ic trackall
option is on by default (see the
.Ic set
command below).
.It Fl l
Login shell.
If the basename the shell is called with (i.e. argv[0])
starts with
.Ql \-
or if this option is used,
the shell is assumed to be a login shell; see
.Sx Startup files
below.
.It Fl p
Privileged shell.
A shell is
.Dq privileged
if the real user ID or group ID does not match the
effective user ID or group ID (see
.Xr getuid 2
and
.Xr getgid 2 ) .
Clearing the privileged option causes the shell to set
its effective user ID (group ID) to its real user ID (group ID).
For further implications, see
.Sx Startup files .
If the shell is privileged and this flag is not explicitly set, the
.Dq privileged
option is cleared automatically after processing the startup files.
.It Fl r
Restricted shell.
A shell is
.Dq restricted
if this
option is used.
The following restrictions come into effect after the shell processes any
profile and
.Ev ENV
files:
.Pp
.Bl -bullet -compact
.It
The
.Ic cd
.Po and Ic chdir Pc
command is disabled.
.It
The
.Ev SHELL ,
.Ev ENV ,
and
.Ev PATH
parameters cannot be changed.
.It
Command names can't be specified with absolute or relative paths.
.It
The
.Fl p
option of the built-in command
.Ic command
can't be used.
.It
Redirections that create files can't be used (i.e.\&
.Ql \*(Gt ,
.Ql \*(Gt\*(Ba ,
.Ql \*(Gt\*(Gt ,
.Ql \*(Lt\*(Gt ) .
.El
.It Fl s
The shell reads commands from standard input; all non-option arguments
are positional parameters.
.It Fl T Ar name
Spawn
.Nm
on the
.Xr tty 4
device given.
The paths
.Ar name ,
.Pa /dev/ttyC Ns Ar name
and
.Pa /dev/tty Ns Ar name
are attempted in order.
Unless
.Ar name
begins with an exclamation mark
.Pq Sq \&! ,
this is done in a subshell and returns immediately.
If
.Ar name
is a dash
.Pq Sq \&\- ,
detach from controlling terminal (daemonise) instead.
.El
.Pp
In addition to the above, the options described in the
.Ic set
built-in command can also be used on the command line:
both
.Op Fl +abCefhkmnuvXx
and
.Op Fl +o Ar option
can be used for single letter or long options, respectively.
.Pp
If neither the
.Fl c
nor the
.Fl s
option is specified, the first non-option argument specifies the name
of a file the shell reads commands from.
If there are no non-option
arguments, the shell reads commands from the standard input.
The name of the shell (i.e. the contents of $0)
is determined as follows: if the
.Fl c
option is used and there is a non-option argument, it is used as the name;
if commands are being read from a file, the file is used as the name;
otherwise, the basename the shell was called with (i.e. argv[0]) is used.
.Pp
The exit status of the shell is 127 if the command file specified on the
command line could not be opened, or non-zero if a fatal syntax error
occurred during the execution of a script.
In the absence of fatal errors,
the exit status is that of the last command executed, or zero, if no
command is executed.
.Ss Startup files
For the actual location of these files, see
.Sx FILES .
A login shell processes the system profile first.
A privileged shell then processes the suid profile.
A non-privileged login shell processes the user profile next.
A non-privileged interactive shell checks the value of the
.Ev ENV
parameter after subjecting it to parameter, command, arithmetic and tilde
.Pq Sq \*(TI
substitution; if unset or empty, the user mkshrc profile is processed;
otherwise, if a file whose name is the substitution result exists,
it is processed; non-existence is silently ignored.
A privileged shell then drops privileges if neither was the
.Fl p
option given on the command line nor set during execution of the startup files.
.Ss Command syntax
The shell begins parsing its input by removing any backslash-newline
combinations, then breaking it into
.Em words .
Words (which are sequences of characters) are delimited by unquoted whitespace
characters (space, tab, and newline) or meta-characters
.Po
.Ql \*(Lt ,
.Ql \*(Gt ,
.Ql \*(Ba ,
.Ql \&; ,
.Ql \&( ,
.Ql \&) ,
and
.Ql &
.Pc .
Aside from delimiting words, spaces and tabs are ignored, while newlines
usually delimit commands.
The meta-characters are used in building the following
.Em tokens :
.Ql \*(Lt ,
.Ql \*(Lt& ,
.Ql \*(Lt\*(Lt ,
.Ql \*(Lt\*(Lt\*(Lt ,
.Ql \*(Gt ,
.Ql \*(Gt& ,
.Ql \*(Gt\*(Gt ,
.Ql &\*(Gt ,
etc. are used to specify redirections (see
.Sx Input/output redirection
below);
.Ql \*(Ba
is used to create pipelines;
.Ql \*(Ba&
is used to create co-processes (see
.Sx Co-processes
below);
.Ql \&;
is used to separate commands;
.Ql &
is used to create asynchronous pipelines;
.Ql &&
and
.Ql \*(Ba\*(Ba
are used to specify conditional execution;
.Ql ;; ,
.Ql ;&\&
and
.Ql ;\*(Ba\&
are used in
.Ic case
statements;
.Ql \&(( .. ))
is used in arithmetic expressions;
and lastly,
.Ql \&( .. )\&
is used to create subshells.
.Pp
Whitespace and meta-characters can be quoted individually using a backslash
.Pq Sq \e ,
or in groups using double
.Pq Sq \&"
or single
.Pq Dq \*(aq
quotes.
Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves:
.Ql \e ,
.Ql \&" ,
.Ql \*(aq ,
.Ql # ,
.Ql $ ,
.Ql \` ,
.Ql \*(TI ,
.Ql { ,
.Ql } ,
.Ql * ,
.Ql \&? ,
and
.Ql \&[ .
The first three of these are the above mentioned quoting characters (see
.Sx Quoting
below);
.Ql # ,
if used at the beginning of a word, introduces a comment \*(en everything after
the
.Ql #
up to the nearest newline is ignored;
.Ql $
is used to introduce parameter, command, and arithmetic substitutions (see
.Sx Substitution
below);
.Ql \`
introduces an old-style command substitution (see
.Sx Substitution
below);
.Ql \*(TI
begins a directory expansion (see
.Sx Tilde expansion
below);
.Ql {
and
.Ql }
delimit
.Xr csh 1 Ns -style
alternations (see
.Sx Brace expansion
below);
and finally,
.Ql * ,
.Ql \&? ,
and
.Ql \&[
are used in file name generation (see
.Sx File name patterns
below).
.Pp
As words and tokens are parsed, the shell builds commands, of which there
are two basic types:
.Em simple-commands ,
typically programmes that are executed, and
.Em compound-commands ,
such as
.Ic for
and
.Ic if
statements, grouping constructs, and function definitions.
.Pp
A simple-command consists of some combination of parameter assignments
(see
.Sx Parameters
below),
input/output redirections (see
.Sx Input/output redirections
below),
and command words; the only restriction is that parameter assignments come
before any command words.
The command words, if any, define the command
that is to be executed and its arguments.
The command may be a shell built-in command, a function,
or an external command
(i.e. a separate executable file that is located using the
.Ev PATH
parameter; see
.Sx Command execution
below).
Note that all command constructs have an exit status: for external commands,
this is related to the status returned by
.Xr wait 2
(if the command could not be found, the exit status is 127; if it could not
be executed, the exit status is 126); the exit status of other command
constructs (built-in commands, functions, compound-commands, pipelines, lists,
etc.) are all well-defined and are described where the construct is
described.
The exit status of a command consisting only of parameter
assignments is that of the last command substitution performed during the
parameter assignment or 0 if there were no command substitutions.
.Pp
Commands can be chained together using the
.Ql \*(Ba
token to form pipelines, in which the standard output of each command but the
last is piped (see
.Xr pipe 2 )
to the standard input of the following command.
The exit status of a pipeline is that of its last command, unless the
.Ic pipefail
option is set (see there).
All commands of a pipeline are executed in separate subshells;
this is allowed by POSIX but differs from both variants of
.At
.Nm ksh ,
where all but the last command were executed in subshells; see the
.Ic read
builtin's description for implications and workarounds.
A pipeline may be prefixed by the
.Ql \&!
reserved word which causes the exit status of the pipeline to be logically
complemented: if the original status was 0, the complemented status will be 1;
if the original status was not 0, the complemented status will be 0.
.Pp
.Em Lists
of commands can be created by separating pipelines by any of the following
tokens:
.Ql && ,
.Ql \*(Ba\*(Ba ,
.Ql & ,
.Ql \*(Ba& ,
and
.Ql \&; .
The first two are for conditional execution:
.Dq Ar cmd1 No && Ar cmd2
executes
.Ar cmd2
only if the exit status of
.Ar cmd1
is zero;
.Ql \*(Ba\*(Ba
is the opposite \*(en
.Ar cmd2
is executed only if the exit status of
.Ar cmd1
is non-zero.
.Ql &&
and
.Ql \*(Ba\*(Ba
have equal precedence which is higher than that of
.Ql & ,
.Ql \*(Ba& ,
and
.Ql \&; ,
which also have equal precedence.
Note that the
.Ql &&
and
.Ql \*(Ba\*(Ba
operators are
.Qq left-associative .
For example, both of these commands will print only
.Qq bar :
.Bd -literal -offset indent
$ false && echo foo \*(Ba\*(Ba echo bar
$ true \*(Ba\*(Ba echo foo && echo bar
.Ed
.Pp
The
.Ql &
token causes the preceding command to be executed asynchronously; that is,
the shell starts the command but does not wait for it to complete (the shell
does keep track of the status of asynchronous commands; see
.Sx Job control
below).
When an asynchronous command is started when job control is disabled
(i.e. in most scripts), the command is started with signals
.Dv SIGINT
and
.Dv SIGQUIT
ignored and with input redirected from
.Pa /dev/null
(however, redirections specified in the asynchronous command have precedence).
The
.Ql \*(Ba&
operator starts a co-process which is a special kind of asynchronous process
(see
.Sx Co-processes
below).
Note that a command must follow the
.Ql &&
and
.Ql \*(Ba\*(Ba
operators, while it need not follow
.Ql & ,
.Ql \*(Ba& ,
or
.Ql \&; .
The exit status of a list is that of the last command executed, with the
exception of asynchronous lists, for which the exit status is 0.
.Pp
Compound commands are created using the following reserved words.
These words
are only recognised if they are unquoted and if they are used as the first
word of a command (i.e. they can't be preceded by parameter assignments or
redirections):
.Bd -literal -offset indent
case     else     function     then      !       (
do       esac     if           time      [[      ((
done     fi       in           until     {
elif     for      select       while     }
.Ed
.Pp
In the following compound command descriptions, command lists (denoted as
.Em list )
that are followed by reserved words must end with a semicolon, a newline, or
a (syntactically correct) reserved word.
For example, the following are all valid:
.Bd -literal -offset indent
$ { echo foo; echo bar; }
$ { echo foo; echo bar\*(Ltnewline\*(Gt}
$ { { echo foo; echo bar; } }
.Ed
.Pp
This is not valid:
.Pp
.Dl $ { echo foo; echo bar }
.Bl -tag -width 4n
.It Pq Ar list
Execute
.Ar list
in a subshell.
There is no implicit way to pass environment changes from a
subshell back to its parent.
.It { Ar list ; No }
Compound construct;
.Ar list
is executed, but not in a subshell.
Note that
.Ql {
and
.Ql }
are reserved words, not meta-characters.
.It Xo case Ar word No in
.Oo Op \&(
.Ar pattern
.Op \*(Ba Ar pattern
.No ... Ns )
.Ar list
.Ic terminator
.Oc No ... esac
.Xc
The
.Ic case
statement attempts to match
.Ar word
against a specified
.Ar pattern ;
the
.Ar list
associated with the first successfully matched pattern is executed.
Patterns used in
.Ic case
statements are the same as those used for file name patterns except that the
restrictions regarding
.Ql \&.
and
.Ql /
are dropped.
Note that any unquoted space before and after a pattern is
stripped; any space within a pattern must be quoted.
Both the word and the
patterns are subject to parameter, command, and arithmetic substitution, as
well as tilde substitution.
.Pp
For historical reasons, open and close braces may be used instead of
.Ic in
and
.Ic esac
e.g.\&
.Ic case $foo { *) echo bar ;; } .
.Pp
The list
.Ic terminator Ns s
are:
.Bl -tag -width 4n
.It Ql ;;
Terminate after the list.
.It Ql ;&\&
Fall through into the next list.
.It Ql ;\*(Ba\&
Evaluate the remaining pattern-list tuples.
.El
.Pp
The exit status of a
.Ic case
statement is that of the executed
.Ar list ;
if no
.Ar list
is executed, the exit status is zero.
.It Xo for Ar name
.Oo in Ar word No ... Oc ;
.No do Ar list ; No done
.Xc
For each
.Ar word
in the specified word list, the parameter
.Ar name
is set to the word and
.Ar list
is executed.
If
.Ic in
is not used to specify a word list, the positional parameters
($1, $2, etc.)\&
are used instead.
For historical reasons, open and close braces may be used instead of
.Ic do
and
.Ic done
e.g.\&
.Ic for i; { echo $i; } .
The exit status of a
.Ic for
statement is the last exit status of
.Ar list ;
if
.Ar list
is never executed, the exit status is zero.
.It Xo if Ar list ;
.No then Ar list ;
.Oo elif Ar list ;
.No then Ar list ; Oc
.No ...
.Oo else Ar list ; Oc
.No fi
.Xc
If the exit status of the first
.Ar list
is zero, the second
.Ar list
is executed; otherwise, the
.Ar list
following the
.Ic elif ,
if any, is executed with similar consequences.
If all the lists following the
.Ic if
and
.Ic elif Ns s
fail (i.e. exit with non-zero status), the
.Ar list
following the
.Ic else
is executed.
The exit status of an
.Ic if
statement is that of non-conditional
.Ar list
that is executed; if no non-conditional
.Ar list
is executed, the exit status is zero.
.It Xo select Ar name
.Oo in Ar word No ... Oc ;
.No do Ar list ; No done
.Xc
The
.Ic select
statement provides an automatic method of presenting the user with a menu and
selecting from it.
An enumerated list of the specified
.Ar word Ns (s)
is printed on standard error, followed by a prompt
.Po
.Ev PS3: normally
.Sq #?\ \&
.Pc .
A number corresponding to one of the enumerated words is then read from
standard input,
.Ar name
is set to the selected word (or unset if the selection is not valid),
.Ev REPLY
is set to what was read (leading/trailing space is stripped), and
.Ar list
is executed.
If a blank line (i.e. zero or more
.Ev IFS
octets) is entered, the menu is reprinted without executing
.Ar list .
.Pp
When
.Ar list
completes, the enumerated list is printed if
.Ev REPLY
is
.Dv NULL ,
the prompt is printed, and so on.
This process continues until an end-of-file
is read, an interrupt is received, or a
.Ic break
statement is executed inside the loop.
If
.Dq in word ...
is omitted, the positional parameters are used
(i.e. $1, $2, etc.).
For historical reasons, open and close braces may be used instead of
.Ic do
and
.Ic done
e.g.\&
.Ic select i; { echo $i; } .
The exit status of a
.Ic select
statement is zero if a
.Ic break
statement is used to exit the loop, non-zero otherwise.
.It Xo until Ar list ;
.No do Ar list ;
.No done
.Xc
This works like
.Ic while ,
except that the body is executed only while the exit status of the first
.Ar list
is non-zero.
.It Xo while Ar list ;
.No do Ar list ;
.No done
.Xc
A
.Ic while
is a pre-checked loop.
Its body is executed as often as the exit status of the first
.Ar list
is zero.
The exit status of a
.Ic while
statement is the last exit status of the
.Ar list
in the body of the loop; if the body is not executed, the exit status is zero.
.It Xo function Ar name
.No { Ar list ; No }
.Xc
Defines the function
.Ar name
(see
.Sx Functions
below).
Note that redirections specified after a function definition are
performed whenever the function is executed, not when the function definition
is executed.
.It Ar name Ns \&() Ar command
Mostly the same as
.Ic function
(see
.Sx Functions
below).
Whitespace (space or tab) after
.Ar name
will be ignored most of the time.
.It Xo function Ar name Ns \&()
.No { Ar list ; No }
.Xc
The same as
.Ar name Ns \&()
.Pq Nm bash Ns ism .
The
.Ic function
keyword is ignored.
.It Xo Ic time Op Fl p
.Op Ar pipeline
.Xc
The
.Sx Command execution
section describes the
.Ic time
reserved word.
.It \&(( Ar expression No ))
The arithmetic expression
.Ar expression
is evaluated; equivalent to
.Dq let expression
(see
.Sx Arithmetic expressions
and the
.Ic let
command, below) in a compound construct.
.It Bq Bq Ar \ \&expression\ \&
Similar to the
.Ic test
and
.Ic \&[ ... \&]
commands (described later), with the following exceptions:
.Bl -bullet
.It
Field splitting and file name generation are not performed on arguments.
.It
The
.Fl a
.Pq AND
and
.Fl o
.Pq OR
operators are replaced with
.Ql &&
and
.Ql \*(Ba\*(Ba ,
respectively.
.It
Operators (e.g.\&
.Sq Fl f ,
.Sq = ,
.Sq \&! )
must be unquoted.
.It
Parameter, command, and arithmetic substitutions are performed as expressions
are evaluated and lazy expression evaluation is used for the
.Ql &&
and
.Ql \*(Ba\*(Ba
operators.
This means that in the following statement,
.Ic $(\*(Ltfoo)
is evaluated if and only if the file
.Pa foo
exists and is readable:
.Bd -literal -offset indent
$ [[ \-r foo && $(\*(Ltfoo) = b*r ]]
.Ed
.It
The second operand of the
.Sq !=
and
.Sq =
expressions are a subset of patterns (e.g. the comparison
.Ic \&[[ foobar = f*r ]]
succeeds).
This even works indirectly:
.Bd -literal -offset indent
$ bar=foobar; baz=\*(aqf*r\*(aq
$ [[ $bar = $baz ]]; echo $?
$ [[ $bar = \&"$baz" ]]; echo $?
.Ed
.Pp
Perhaps surprisingly, the first comparison succeeds,
whereas the second doesn't.
This does not apply to all extglob metacharacters, currently.
.El
.El
.Ss Quoting
Quoting is used to prevent the shell from treating characters or words
specially.
There are three methods of quoting.
First,
.Ql \e
quotes the following character, unless it is at the end of a line, in which
case both the
.Ql \e
and the newline are stripped.
Second, a single quote
.Pq Dq \*(aq
quotes everything up to the next single quote (this may span lines).
Third, a double quote
.Pq Sq \&"
quotes all characters, except
.Ql $ ,
.Ql \`
and
.Ql \e ,
up to the next unquoted double quote.
.Ql $
and
.Ql \`
inside double quotes have their usual meaning (i.e. parameter, arithmetic,
or command substitution) except no field splitting is carried out on the
results of double-quoted substitutions.
If a
.Ql \e
inside a double-quoted string is followed by
.Ql \e ,
.Ql $ ,
.Ql \` ,
or
.Ql \&" ,
it is replaced by the second character; if it is followed by a newline, both
the
.Ql \e
and the newline are stripped; otherwise, both the
.Ql \e
and the character following are unchanged.
.Pp
If a single-quoted string is preceded by an unquoted
.Ql $ ,
C style backslash expansion (see below) is applied (even single quote
characters inside can be escaped and do not terminate the string then);
the expanded result is treated as any other single-quoted string.
If a double-quoted string is preceded by an unquoted
.Ql $ ,
the
.Ql $
is simply ignored.
.Ss Backslash expansion
In places where backslashes are expanded, certain C and
.At
.Nm ksh
or GNU
.Nm bash
style escapes are translated.
These include
.Ql \ea ,
.Ql \eb ,
.Ql \ef ,
.Ql \en ,
.Ql \er ,
.Ql \et ,
.Ql \eU######## ,
.Ql \eu#### ,
and
.Ql \ev .
For
.Ql \eU########
and
.Ql \eu#### ,
.Dq #
means a hexadecimal digit, of thich there may be none up to four or eight;
these escapes translate a Unicode codepoint to UTF-8.
Furthermore,
.Ql \eE
and
.Ql \ee
expand to the escape character.
.Pp
In the
.Ic print
builtin mode,
.Ql \e" ,
.Ql \e\*(aq ,
and
.Ql \e?
are explicitly excluded;
octal sequences must have the none up to three octal digits
.Dq #
prefixed with the digit zero
.Pq Ql \e0### ;
hexadecimal sequences
.Ql \ex##
are limited to none up to two hexadecimal digits
.Dq # ;
both octal and hexadecimal sequences convert to raw octets;
.Ql \e# ,
where # is none of the above, translates to \e# (backslashes are retained).
.Pp
Backslash expansion in the C style mode slightly differs: octal sequences
.Ql \e###
must have no digit zero prefixing the one up to three octal digits
.Dq #
and yield raw octets; hexadecimal sequences
.Ql \ex#*
greedily eat up as many hexadecimal digits
.Dq #
as they can and terminate with the first non-hexadecimal digit;
these translate a Unicode codepoint to UTF-8.
The sequence
.Ql \ec# ,
where
.Dq #
is any octet, translates to Ctrl-# (which basically means,
.Ql \ec?
becomes DEL, everything else is bitwise ANDed with 0x1F).
Finally,
.Ql \e# ,
where # is none of the above, translates to # (has the backslash trimmed),
even if it is a newline.
.Ss Aliases
There are two types of aliases: normal command aliases and tracked aliases.
Command aliases are normally used as a short hand for a long or often used
command.
The shell expands command aliases (i.e. substitutes the alias name
for its value) when it reads the first word of a command.
An expanded alias is re-processed to check for more aliases.
If a command alias ends in a
space or tab, the following word is also checked for alias expansion.
The alias expansion process stops when a word that is not an alias is found,
when a quoted word is found, or when an alias word that is currently being
expanded is found.
Aliases are specifically an interactive feature: while they do happen
to work in scripts and on the command line in some cases, aliases are
expanded during lexing, so their use must be in a separate command tree
from their definition; otherwise, the alias will not be found.
Noticeably, command lists (separated by semicolon, in command substitutions
also by newline) may be one same parse tree.
.Pp
The following command aliases are defined automatically by the shell:
.Bd -literal -offset indent
autoload=\*(aq\etypeset \-fu\*(aq
functions=\*(aq\etypeset \-f\*(aq
hash=\*(aq\ebuiltin alias \-t\*(aq
history=\*(aq\ebuiltin fc \-l\*(aq
integer=\*(aq\etypeset \-i\*(aq
local=\*(aq\etypeset\*(aq
login=\*(aq\eexec login\*(aq
nameref=\*(aq\etypeset \-n\*(aq
nohup=\*(aqnohup \*(aq
r=\*(aq\ebuiltin fc \-e \-\*(aq
type=\*(aq\ebuiltin whence \-v\*(aq
.Ed
.Pp
Tracked aliases allow the shell to remember where it found a particular
command.
The first time the shell does a path search for a command that is
marked as a tracked alias, it saves the full path of the command.
The next
time the command is executed, the shell checks the saved path to see that it
is still valid, and if so, avoids repeating the path search.
Tracked aliases can be listed and created using
.Ic alias Fl t .
Note that changing the
.Ev PATH
parameter clears the saved paths for all tracked aliases.
If the
.Ic trackall
option is set (i.e.\&
.Ic set Fl o Ic trackall
or
.Ic set Fl h ) ,
the shell tracks all commands.
This option is set automatically for non-interactive shells.
For interactive shells, only the following commands are
automatically tracked:
.Xr cat 1 ,
.Xr cc 1 ,
.Xr chmod 1 ,
.Xr cp 1 ,
.Xr date 1 ,
.Xr ed 1 ,
.Xr emacs 1 ,
.Xr grep 1 ,
.Xr ls 1 ,
.Xr make 1 ,
.Xr mv 1 ,
.Xr pr 1 ,
.Xr rm 1 ,
.Xr sed 1 ,
.Xr sh 1 ,
.Xr vi 1 ,
and
.Xr who 1 .
.Ss Substitution
The first step the shell takes in executing a simple-command is to perform
substitutions on the words of the command.
There are three kinds of
substitution: parameter, command, and arithmetic.
Parameter substitutions,
which are described in detail in the next section, take the form
.Pf $ Ns Ar name
or
.Pf ${ Ns Ar ... Ns } ;
command substitutions take the form
.Pf $( Ns Ar command Ns \&)
or (deprecated)
.Pf \` Ns Ar command Ns \`
or (executed in the current environment)
.Pf ${\ \& Ar command Ns \&;}
and strip trailing newlines;
and arithmetic substitutions take the form
.Pf $(( Ns Ar expression Ns )) .
Parsing the current-environment command substitution requires a space,
tab or newline after the opening brace and that the closing brace be
recognised as a keyword (i.e. is preceded by a newline or semicolon).
They are also called funsubs (function substitutions) and behave like
functions in that
.Ic local
and
.Ic return
work, and in that
.Ic exit
terminates the parent shell; shell options are shared.
.Pp
Another variant of substitution are the valsubs (value substitutions)
.Pf ${\*(Ba\& Ns Ar command Ns \&;}
which are also executed in the current environment, like funsubs, but
share their I/O with the parent; instead, they evaluate to whatever
the, initially empty, expression-local variable
.Ev REPLY
is set to within the
.Ar command Ns s .
.Pp
If a substitution appears outside of double quotes, the results of the
substitution are generally subject to word or field splitting according to
the current value of the
.Ev IFS
parameter.
The
.Ev IFS
parameter specifies a list of octets which are used to break a string up
into several words; any octets from the set space, tab, and newline that
appear in the
.Ev IFS
octets are called
.Dq IFS whitespace .
Sequences of one or more
.Ev IFS
whitespace octets, in combination with zero or one
.Pf non- Ev IFS
whitespace octets, delimit a field.
As a special case, leading and trailing
.Ev IFS
whitespace is stripped (i.e. no leading or trailing empty field
is created by it); leading or trailing
.Pf non- Ev IFS
whitespace does create an empty field.
.Pp
Example: If
.Ev IFS
is set to
.Dq \*(Ltspace\*(Gt: ,
and VAR is set to
.Dq \*(Ltspace\*(GtA\*(Ltspace\*(Gt:\*(Ltspace\*(Gt\*(Ltspace\*(GtB::D ,
the substitution for $VAR results in four fields:
.Sq A ,
.Sq B ,
.Sq
(an empty field),
and
.Sq D .
Note that if the
.Ev IFS
parameter is set to the empty string, no field splitting is done;
if it is unset, the default value of space, tab, and newline is used.
.Pp
Also, note that the field splitting applies only to the immediate result of
the substitution.
Using the previous example, the substitution for $VAR:E
results in the fields:
.Sq A ,
.Sq B ,
.Sq ,
and
.Sq D:E ,
not
.Sq A ,
.Sq B ,
.Sq ,
.Sq D ,
and
.Sq E .
This behavior is POSIX compliant, but incompatible with some other shell
implementations which do field splitting on the word which contained the
substitution or use
.Dv IFS
as a general whitespace delimiter.
.Pp
The results of substitution are, unless otherwise specified, also subject to
brace expansion and file name expansion (see the relevant sections below).
.Pp
A command substitution is replaced by the output generated by the specified
command which is run in a subshell.
For
.Pf $( Ns Ar command Ns \&)
and
.Pf ${\*(Ba\& Ns Ar command Ns \&;}
and
.Pf ${\ \& Ar command Ns \&;}
substitutions, normal quoting rules are used when
.Ar command
is parsed; however, for the deprecated
.Pf \` Ns Ar command Ns \`
form, a
.Ql \e
followed by any of
.Ql $ ,
.Ql \` ,
.Ql \&"
.Pq currently, and violating Tn POSIX ,
or
.Ql \e
is stripped (a
.Ql \e
followed by any other character is unchanged).
As a special case in command substitutions, a command of the form
.Pf \*(Lt Ar file
is interpreted to mean substitute the contents of
.Ar file .
Note that
.Ic $(\*(Ltfoo)
has the same effect as
.Ic $(cat foo) .
.Pp
Note that some shells do not use a recursive parser for command substitutions,
leading to failure for certain constructs; to be portable, use as workaround
.Ql x=$(cat) \*(Lt\*(Lt"EOF"
(or the newline-keeping
.Ql x=\*(Lt\*(Lt"EOF"
extension) instead to merely slurp the string.
.St -p1003.1
recommends to use case statements of the form
.Ql "x=$(case $foo in (bar) echo $bar ;; (*) echo $baz ;; esac)"
instead, which would work but not serve as example for this portability issue.
.Bd -literal -offset indent
x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
# above fails to parse on old shells; below is the workaround
x=$(eval $(cat)) \*(Lt\*(Lt"EOF"
case $foo in bar) echo $bar ;; *) echo $baz ;; esac
EOF
.Ed
.Pp
Arithmetic substitutions are replaced by the value of the specified expression.
For example, the command
.Ic print $((2+3*4))
displays 14.
See
.Sx Arithmetic expressions
for a description of an expression.
.Ss Parameters
Parameters are shell variables; they can be assigned values and their values
can be accessed using a parameter substitution.
A parameter name is either one
of the special single punctuation or digit character parameters described
below, or a letter followed by zero or more letters or digits
.Po
.Ql _
counts as a letter
.Pc .
The latter form can be treated as arrays by appending an array index of the
form
.Op Ar expr
where
.Ar expr
is an arithmetic expression.
Array indices in
.Nm
are limited to the range 0 through 4294967295, inclusive.
That is, they are a 32-bit unsigned integer.
.Pp
Parameter substitutions take the form
.Pf $ Ns Ar name ,
.Pf ${ Ns Ar name Ns } ,
or
.Sm off
.Pf ${ Ar name Oo Ar expr Oc }
.Sm on
where
.Ar name
is a parameter name.
Substitution of all array elements with
.Pf ${ Ns Ar name Ns \&[*]}
and
.Pf ${ Ns Ar name Ns \&[@]}
works equivalent to $* and $@ for positional parameters.
If substitution is performed on a parameter
(or an array parameter element)
that is not set, a null string is substituted unless the
.Ic nounset
option
.Po
.Ic set Fl o Ic nounset
or
.Ic set Fl u
.Pc
is set, in which case an error occurs.
.Pp
Parameters can be assigned values in a number of ways.
First, the shell implicitly sets some parameters like
.Ql # ,
.Ql PWD ,
and
.Ql $ ;
this is the only way the special single character parameters are set.
Second, parameters are imported from the shell's environment at startup.
Third, parameters can be assigned values on the command line: for example,
.Ic FOO=bar
sets the parameter
.Dq FOO
to
.Dq bar ;
multiple parameter assignments can be given on a single command line and they
can be followed by a simple-command, in which case the assignments are in
effect only for the duration of the command (such assignments are also
exported; see below for the implications of this).
Note that both the parameter name and the
.Ql =
must be unquoted for the shell to recognise a parameter assignment.
The construct
.Ic FOO+=baz
is also recognised; the old and new values are immediately concatenated.
The fourth way of setting a parameter is with the
.Ic export ,
.Ic global ,
.Ic readonly ,
and
.Ic typeset
commands; see their descriptions in the
.Sx Command execution
section.
Fifth,
.Ic for
and
.Ic select
loops set parameters as well as the
.Ic getopts ,
.Ic read ,
and
.Ic set Fl A
commands.
Lastly, parameters can be assigned values using assignment operators
inside arithmetic expressions (see
.Sx Arithmetic expressions
below) or using the
.Sm off
.Pf ${ Ar name No = Ar value No }
.Sm on
form of the parameter substitution (see below).
.Pp
Parameters with the export attribute (set using the
.Ic export
or
.Ic typeset Fl x
commands, or by parameter assignments followed by simple commands) are put in
the environment (see
.Xr environ 7 )
of commands run by the shell as
.Ar name Ns = Ns Ar value
pairs.
The order in which parameters appear in the environment of a command is
unspecified.
When the shell starts up, it extracts parameters and their values
from its environment and automatically sets the export attribute for those
parameters.
.Pp
Modifiers can be applied to the
.Pf ${ Ns Ar name Ns }
form of parameter substitution:
.Bl -tag -width Ds
.Sm off
.It ${ Ar name No :\- Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
it is substituted; otherwise,
.Ar word
is substituted.
.Sm off
.It ${ Ar name No :+ Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
.Ar word
is substituted; otherwise, nothing is substituted.
.Sm off
.It ${ Ar name No := Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
it is substituted; otherwise, it is assigned
.Ar word
and the resulting value of
.Ar name
is substituted.
.Sm off
.It ${ Ar name No :? Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
it is substituted; otherwise,
.Ar word
is printed on standard error (preceded by
.Ar name : )
and an error occurs (normally causing termination of a shell script, function,
or script sourced using the
.Sq \&.
built-in).
If
.Ar word
is omitted, the string
.Dq parameter null or not set
is used instead.
Currently a bug, if
.Ar word
is a variable which expands to the null string, the
error message is also printed.
.El
.Pp
Note that, for all of the above,
.Ar word
is actually considered quoted, and special parsing rules apply.
The parsing rules also differ on whether the expression is double-quoted:
.Ar word
then uses double-quoting rules, except for the double quote itself
.Pq Sq \&"
and the closing brace, which, if backslash escaped, gets quote removal applied.
.Pp
In the above modifiers, the
.Ql \&:
can be omitted, in which case the conditions only depend on
.Ar name
being set (as opposed to set and not
.Dv NULL ) .
If
.Ar word
is needed, parameter, command, arithmetic, and tilde substitution are performed
on it; if
.Ar word
is not needed, it is not evaluated.
.Pp
The following forms of parameter substitution can also be used (if
.Ar name
is an array, the element with the key
.Dq 0
will be substituted in scalar context):
.Pp
.Bl -tag -width Ds -compact
.It Pf ${# Ns Ar name Ns \&}
The number of positional parameters if
.Ar name
is
.Ql * ,
.Ql @ ,
or not specified; otherwise the length
.Pq in characters
of the string value of parameter
.Ar name .
.Pp
.It Pf ${# Ns Ar name Ns \&[*]}
.It Pf ${# Ns Ar name Ns \&[@]}
The number of elements in the array
.Ar name .
.Pp
.It Pf ${% Ns Ar name Ns \&}
The width
.Pq in screen columns
of the string value of parameter
.Ar name ,
or \-1 if
.Pf ${ Ns Ar name Ns }
contains a control character.
.Pp
.It Pf ${! Ns Ar name Ns }
The name of the variable referred to by
.Ar name .
This will be
.Ar name
except when
.Ar name
is a name reference (bound variable), created by the
.Ic nameref
command (which is an alias for
.Ic typeset Fl n ) .
.Pp
.It Pf ${! Ns Ar name Ns \&[*]}
.It Pf ${! Ns Ar name Ns \&[@]}
The names of indices (keys) in the array
.Ar name .
.Pp
.Sm off
.It Xo
.Pf ${ Ar name
.Pf # Ar pattern No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf ## Ar pattern No }
.Xc
.Sm on
If
.Ar pattern
matches the beginning of the value of parameter
.Ar name ,
the matched text is deleted from the result of substitution.
A single
.Ql #
results in the shortest match, and two
of them result in the longest match.
Cannot be applied to a vector
.Pq ${*} or ${@} or ${array[*]} or ${array[@]} .
.Pp
.Sm off
.It Xo
.Pf ${ Ar name
.Pf % Ar pattern No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf %% Ar pattern No }
.Xc
.Sm on
Like ${..#..} substitution, but it deletes from the end of the value.
Cannot be applied to a vector.
.Pp
.Sm off
.It Xo
.Pf ${ Ar name
.Pf / Ar pattern / Ar string No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf /# Ar pattern / Ar string No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf /% Ar pattern / Ar string No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf // Ar pattern / Ar string No }
.Xc
.Sm on
The longest match of
.Ar pattern
in the value of parameter
.Ar name
is replaced with
.Ar string
(deleted if
.Ar string
is empty; the trailing slash
.Pq Ql /
may be omitted in that case).
A leading slash followed by
.Ql #
or
.Ql %
causes the pattern to be anchored at the beginning or end of
the value, respectively; empty unanchored
.Ar pattern Ns s
cause no replacement; a single leading slash or use of a
.Ar pattern
that matches the empty string causes the replacement to
happen only once; two leading slashes cause all occurrences
of matches in the value to be replaced.
Cannot be applied to a vector.
Inefficiently implemented, may be slow.
.Pp
.Sm off
.It Xo
.Pf ${ Ar name : Ns Ar pos
.Pf : Ns Ar len Ns }
.Xc
.Sm on
The first
.Ar len
characters of
.Ar name ,
starting at position
.Ar pos ,
are substituted.
Both
.Ar pos
and
.Pf : Ns Ar len
are optional.
If
.Ar pos
is negative, counting starts at the end of the string; if it
is omitted, it defaults to 0.
If
.Ar len
is omitted or greater than the length of the remaining string,
all of it is substituted.
Both
.Ar pos
and
.Ar len
are evaluated as arithmetic expressions.
Currently,
.Ar pos
must start with a space, opening parenthesis or digit to be recognised.
Cannot be applied to a vector.
.Pp
.It Pf ${ Ns Ar name Ns @#}
The hash (using the BAFH algorithm) of the expansion of
.Ar name .
This is also used internally for the shell's hashtables.
.Pp
.It Pf ${ Ns Ar name Ns @Q}
A quoted expression safe for re-entry, whose value is the value of the
.Ar name
parameter, is substituted.
.El
.Pp
Note that
.Ar pattern
may need extended globbing pattern
.Pq @(...) ,
single
.Pq \&\*(aq...\&\*(aq
or double
.Pq \&"...\&"
quote escaping unless
.Fl o Ic sh
is set.
.Pp
The following special parameters are implicitly set by the shell and cannot be
set directly using assignments:
.Bl -tag -width "1 .. 9"
.It Ev \&!
Process ID of the last background process started.
If no background processes have been started, the parameter is not set.
.It Ev \&#
The number of positional parameters ($1, $2, etc.).
.It Ev \&$
The PID of the shell, or the PID of the original shell if it is a subshell.
Do
.Em NOT
use this mechanism for generating temporary file names; see
.Xr mktemp 1
instead.
.It Ev \-
The concatenation of the current single letter options (see the
.Ic set
command below for a list of options).
.It Ev \&?
The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal,
.Ic $?\&
is set to 128 plus the signal number, but at most 255.
.It Ev 0
The name of the shell, determined as follows:
the first argument to
.Nm
if it was invoked with the
.Fl c
option and arguments were given; otherwise the
.Ar file
argument, if it was supplied;
or else the basename the shell was invoked with (i.e.\&
.Li argv[0] ) .
.Ev $0
is also set to the name of the current script or
the name of the current function, if it was defined with the
.Ic function
keyword (i.e. a Korn shell style function).
.It Ev 1 No .. Ev 9
The first nine positional parameters that were supplied to the shell, function,
or script sourced using the
.Sq \&.
built-in.
Further positional parameters may be accessed using
.Pf ${ Ar number Ns } .
.It Ev *
All positional parameters (except 0), i.e. $1, $2, $3, ...
.br
If used
outside of double quotes, parameters are separate words (which are subjected
to word splitting); if used within double quotes, parameters are separated
by the first character of the
.Ev IFS
parameter (or the empty string if
.Ev IFS
is
.Dv NULL ) .
.It Ev @
Same as
.Ic $* ,
unless it is used inside double quotes, in which case a separate word is
generated for each positional parameter.
If there are no positional parameters, no word is generated.
.Ic $@
can be used to access arguments, verbatim, without losing
.Dv NULL
arguments or splitting arguments with spaces.
.El
.Pp
The following parameters are set and/or used by the shell:
.Bl -tag -width "KSH_VERSION"
.It Ev _
.Pq underscore
When an external command is executed by the shell, this parameter is set in the
environment of the new process to the path of the executed command.
In interactive use, this parameter is also set in the parent shell to the last
word of the previous command.
.It Ev BASHPID
The PID of the shell or subshell.
.It Ev CDPATH
Like
.Ev PATH ,
but used to resolve the argument to the
.Ic cd
built-in command.
Note that if
.Ev CDPATH
is set and does not contain
.Sq \&.
or an empty string element, the current directory is not searched.
Also, the
.Ic cd
built-in command will display the resulting directory when a match is found
in any search path other than the empty path.
.It Ev COLUMNS
Set to the number of columns on the terminal or window.
Always set, defaults to 80, unless the
value as reported by
.Xr stty 1
is non-zero and sane enough (minimum is 12x3); similar for
.Ev LINES .
This parameter is used by the interactive line editing modes, and by the
.Ic select ,
.Ic set Fl o ,
and
.Ic kill Fl l
commands to format information columns.
Importing from the environment or unsetting this parameter removes the
binding to the actual terminal size in favour of the provided value.
.It Ev ENV
If this parameter is found to be set after any profile files are executed, the
expanded value is used as a shell startup file.
It typically contains function and alias definitions.
.It Ev ERRNO
Integer value of the shell's
.Va errno
variable.
It indicates the reason the last system call failed.
Not yet implemented.
.It Ev EXECSHELL
If set, this parameter is assumed to contain the shell that is to be used to
execute commands that
.Xr execve 2
fails to execute and which do not start with a
.Dq #! Ns Ar shell
sequence.
.It Ev FCEDIT
The editor used by the
.Ic fc
command (see below).
.It Ev FPATH
Like
.Ev PATH ,
but used when an undefined function is executed to locate the file defining the
function.
It is also searched when a command can't be found using
.Ev PATH .
See
.Sx Functions
below for more information.
.It Ev HISTFILE
The name of the file used to store command history.
When assigned to or unset, the file is opened, history is truncated
then loaded from the file; subsequent new commands (possibly consisting
of several lines) are appended once they successfully compiled.
Also, several invocations of the shell will share history if their
.Ev HISTFILE
parameters all point to the same file.
.Pp
.Sy Note :
If
.Ev HISTFILE
is unset or empty, no history file is used.
This is different from
.At
.Nm ksh .
.It Ev HISTSIZE
The number of commands normally stored for history.
The default is 2047.
Do not set this value to insanely high values such as 1000000000 because
.Nm
can then not allocate enough memory for the history and will not start.
.It Ev HOME
The default directory for the
.Ic cd
command and the value substituted for an unqualified
.Ic \*(TI
(see
.Sx Tilde expansion
below).
.It Ev IFS
Internal field separator, used during substitution and by the
.Ic read
command, to split values into distinct arguments; normally set to space, tab,
and newline.
See
.Sx Substitution
above for details.
.Pp
.Sy Note :
This parameter is not imported from the environment when the shell is
started.
.It Ev KSHEGID
The effective group id of the shell.
.It Ev KSHGID
The real group id of the shell.
.It Ev KSHUID
The real user id of the shell.
.It Ev KSH_VERSION
The name and version of the shell (read-only).
See also the version commands in
.Sx Emacs editing mode
and
.Sx Vi editing mode
sections, below.
.It Ev LINENO
The line number of the function or shell script that is currently being
executed.
.It Ev LINES
Set to the number of lines on the terminal or window.
Always set, defaults to 24.
See
.Ev COLUMNS .
.It Ev EPOCHREALTIME
Time since the epoch, as returned by
.Xr gettimeofday 2 ,
formatted as decimal
.Va tv_sec
followed by a dot
.Pq Sq .\&
and
.Va tv_usec
padded to exactly six decimal digits.
.It Ev OLDPWD
The previous working directory.
Unset if
.Ic cd
has not successfully changed directories since the shell started, or if the
shell doesn't know where it is.
.It Ev OPTARG
When using
.Ic getopts ,
it contains the argument for a parsed option, if it requires one.
.It Ev OPTIND
The index of the next argument to be processed when using
.Ic getopts .
Assigning 1 to this parameter causes
.Ic getopts
to process arguments from the beginning the next time it is invoked.
.It Ev PATH
A colon (semicolon on OS/2) separated list of directories that are
searched when looking for commands and files sourced using the
.Sq \&.
command (see below).
An empty string resulting from a leading or trailing
colon, or two adjacent colons, is treated as a
.Sq \&.
(the current directory).
.It Ev PGRP
The process ID of the shell's process group leader.
.It Ev PIPESTATUS
An array containing the errorlevel (exit status) codes,
one by one, of the last pipeline run in the foreground.
.It Ev PPID
The process ID of the shell's parent.
.It Ev PS1
The primary prompt for interactive shells.
Parameter, command, and arithmetic
substitutions are performed, and
.Ql \&!
is replaced with the current command number (see the
.Ic fc
command below).
A literal
.Ql \&!
can be put in the prompt by placing
.Ql !!
in
.Ev PS1 .
.Pp
The default prompt is
.Sq $\ \&
for non-root users,
.Sq #\ \&
for root.
If
.Nm
is invoked by root and
.Ev PS1
does not contain a
.Sq #
character, the default value will be used even if
.Ev PS1
already exists in the environment.
.Pp
The
.Nm
distribution comes with a sample
.Pa dot.mkshrc
containing a sophisticated example, but you might like the following one
(note that ${HOSTNAME:=$(hostname)} and the
root-vs-user distinguishing clause are (in this example) executed at
.Ev PS1
assignment time, while the $USER and $PWD are escaped
and thus will be evaluated each time a prompt is displayed):
.Bd -literal
PS1=\*(aq${USER:=$(id \-un)}\*(aq"@${HOSTNAME:=$(hostname)}:\e$PWD $(
	if (( USER_ID )); then print \e$; else print \e#; fi) "
.Ed
.Pp
Note that since the command-line editors try to figure out how long the prompt
is (so they know how far it is to the edge of the screen), escape codes in
the prompt tend to mess things up.
You can tell the shell not to count certain
sequences (such as escape codes) by prefixing your prompt with a
character (such as Ctrl-A) followed by a carriage return and then delimiting
the escape codes with this character.
Any occurrences of that character in the prompt are not printed.
By the way, don't blame me for
this hack; it's derived from the original
.Xr ksh88 1 ,
which did print the delimiter character so you were out of luck
if you did not have any non-printing characters.
.Pp
Since Backslashes and other special characters may be
interpreted by the shell, to set
.Ev PS1
either escape the backslash itself,
or use double quotes.
The latter is more practical.
This is a more complex example,
avoiding to directly enter special characters (for example with
.Ic \*(haV
in the emacs editing mode),
which embeds the current working directory,
in reverse video
.Pq colour would work, too ,
in the prompt string:
.Bd -literal -offset indent
x=$(print \e\e001)
PS1="$x$(print \e\er)$x$(tput so)$x\e$PWD$x$(tput se)$x\*(Gt "
.Ed
.Pp
Due to a strong suggestion from David G. Korn,
.Nm
now also supports the following form:
.Bd -literal -offset indent
PS1=$'\e1\er\e1\ee[7m\e1$PWD\e1\ee[0m\e1\*(Gt '
.Ed
.It Ev PS2
Secondary prompt string, by default
.Sq \*(Gt\ \& ,
used when more input is needed to complete a command.
.It Ev PS3
Prompt used by the
.Ic select
statement when reading a menu selection.
The default is
.Sq #?\ \& .
.It Ev PS4
Used to prefix commands that are printed during execution tracing (see the
.Ic set Fl x
command below).
Parameter, command, and arithmetic substitutions are performed
before it is printed.
The default is
.Sq +\ \& .
You may want to set it to
.Sq \&[$EPOCHREALTIME]\ \&
instead, to include timestamps.
.It Ev PWD
The current working directory.
May be unset or
.Dv NULL
if the shell doesn't know where it is.
.It Ev RANDOM
Each time
.Ev RANDOM
is referenced, it is assigned a number between 0 and 32767 from
a Linear Congruential PRNG first.
.It Ev REPLY
Default parameter for the
.Ic read
command if no names are given.
Also used in
.Ic select
loops to store the value that is read from standard input.
.It Ev SECONDS
The number of seconds since the shell started or, if the parameter has been
assigned an integer value, the number of seconds since the assignment plus the
value that was assigned.
.It Ev TMOUT
If set to a positive integer in an interactive shell, it specifies the maximum
number of seconds the shell will wait for input after printing the primary
prompt
.Pq Ev PS1 .
If the time is exceeded, the shell exits.
.It Ev TMPDIR
The directory temporary shell files are created in.
If this parameter is not
set, or does not contain the absolute path of a writable directory, temporary
files are created in
.Pa /tmp .
.It Ev USER_ID
The effective user id of the shell.
.El
.Ss Tilde expansion
Tilde expansion which is done in parallel with parameter substitution, is done
on words starting with an unquoted
.Ql \*(TI .
The characters following the tilde, up to the first
.Ql / ,
if any, are assumed to be a login name.
If the login name is empty,
.Ql + ,
or
.Ql \- ,
the value of the
.Ev HOME ,
.Ev PWD ,
or
.Ev OLDPWD
parameter is substituted, respectively.
Otherwise, the password file is
searched for the login name, and the tilde expression is substituted with the
user's home directory.
If the login name is not found in the password file or
if any quoting or parameter substitution occurs in the login name, no
substitution is performed.
.Pp
In parameter assignments
(such as those preceding a simple-command or those occurring
in the arguments of
.Ic alias ,
.Ic export ,
.Ic global ,
.Ic readonly ,
and
.Ic typeset ) ,
tilde expansion is done after any assignment
(i.e. after the equals sign)
or after an unquoted colon
.Pq Sq \&: ;
login names are also delimited by colons.
.Pp
The home directory of previously expanded login names are cached and re-used.
The
.Ic alias Fl d
command may be used to list, change, and add to this cache (e.g.\&
.Ic alias \-d fac=/usr/local/facilities; cd \*(TIfac/bin ) .
.Ss Brace expansion (alternation)
Brace expressions take the following form:
.Bd -unfilled -offset indent
.Sm off
.Xo
.Ar prefix No { Ar str1 No ,...,
.Ar strN No } Ar suffix
.Xc
.Sm on
.Ed
.Pp
The expressions are expanded to
.Ar N
words, each of which is the concatenation of
.Ar prefix ,
.Ar str Ns i ,
and
.Ar suffix
(e.g.\&
.Dq a{c,b{X,Y},d}e
expands to four words:
.Dq ace ,
.Dq abXe ,
.Dq abYe ,
and
.Dq ade ) .
As noted in the example, brace expressions can be nested and the resulting
words are not sorted.
Brace expressions must contain an unquoted comma
.Pq Sq \&,
for expansion to occur (e.g.\&
.Ic {}
and
.Ic {foo}
are not expanded).
Brace expansion is carried out after parameter substitution
and before file name generation.
.Ss File name patterns
A file name pattern is a word containing one or more unquoted
.Ql \&? ,
.Ql * ,
.Ql + ,
.Ql @ ,
or
.Ql \&!
characters or
.Dq \&[..]
sequences.
Once brace expansion has been performed, the shell replaces file
name patterns with the sorted names of all the files that match the pattern
(if no files match, the word is left unchanged).
The pattern elements have the following meaning:
.Bl -tag -width Ds
.It \&?
Matches any single character.
.It \&*
Matches any sequence of octets.
.It \&[..]
Matches any of the octets inside the brackets.
Ranges of octets can be specified by separating two octets by a
.Ql \-
(e.g.\&
.Dq \&[a0\-9]
matches the letter
.Sq a
or any digit).
In order to represent itself, a
.Ql \-
must either be quoted or the first or last octet in the octet list.
Similarly, a
.Ql \&]
must be quoted or the first octet in the list if it is to represent itself
instead of the end of the list.
Also, a
.Ql \&!
appearing at the start of the list has special meaning (see below), so to
represent itself it must be quoted or appear later in the list.
.It \&[!..]
Like [..],
except it matches any octet not inside the brackets.
.Sm off
.It *( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches any string of octets that matches zero or more occurrences of the
specified patterns.
Example: The pattern
.Ic *(foo\*(Babar)
matches the strings
.Dq ,
.Dq foo ,
.Dq bar ,
.Dq foobarfoo ,
etc.
.Sm off
.It +( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches any string of octets that matches one or more occurrences of the
specified patterns.
Example: The pattern
.Ic +(foo\*(Babar)
matches the strings
.Dq foo ,
.Dq bar ,
.Dq foobar ,
etc.
.Sm off
.It ?( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches the empty string or a string that matches one of the specified
patterns.
Example: The pattern
.Ic ?(foo\*(Babar)
only matches the strings
.Dq ,
.Dq foo ,
and
.Dq bar .
.Sm off
.It @( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches a string that matches one of the specified patterns.
Example: The pattern
.Ic @(foo\*(Babar)
only matches the strings
.Dq foo
and
.Dq bar .
.Sm off
.It !( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches any string that does not match one of the specified patterns.
Examples: The pattern
.Ic !(foo\*(Babar)
matches all strings except
.Dq foo
and
.Dq bar ;
the pattern
.Ic !(*)
matches no strings; the pattern
.Ic !(?)*\&
matches all strings (think about it).
.El
.Pp
Note that complicated globbing, especially with alternatives,
is slow; using separate comparisons may (or may not) be faster.
.Pp
Note that
.Nm mksh
.Po and Nm pdksh Pc
never matches
.Sq \&.
and
.Sq .. ,
but
.At
.Nm ksh ,
Bourne
.Nm sh ,
and GNU
.Nm bash
do.
.Pp
Note that none of the above pattern elements match either a period
.Pq Sq \&.
at the start of a file name or a slash
.Pq Sq / ,
even if they are explicitly used in a [..] sequence; also, the names
.Sq \&.
and
.Sq ..
are never matched, even by the pattern
.Sq .* .
.Pp
If the
.Ic markdirs
option is set, any directories that result from file name generation are marked
with a trailing
.Ql / .
.Ss Input/output redirection
When a command is executed, its standard input, standard output, and standard
error (file descriptors 0, 1, and 2, respectively) are normally inherited from
the shell.
Three exceptions to this are commands in pipelines, for which
standard input and/or standard output are those set up by the pipeline,
asynchronous commands created when job control is disabled, for which standard
input is initially set to be from
.Pa /dev/null ,
and commands for which any of the following redirections have been specified:
.Bl -tag -width XXxxmarker
.It \*(Gt Ns Ar file
Standard output is redirected to
.Ar file .
If
.Ar file
does not exist, it is created; if it does exist, is a regular file, and the
.Ic noclobber
option is set, an error occurs; otherwise, the file is truncated.
Note that this means the command
.Ic cmd \*(Ltfoo \*(Gtfoo
will open
.Ar foo
for reading and then truncate it when it opens it for writing, before
.Ar cmd
gets a chance to actually read
.Ar foo .
.It \*(Gt\*(Ba Ns Ar file
Same as
.Ic \*(Gt ,
except the file is truncated, even if the
.Ic noclobber
option is set.
.It \*(Gt\*(Gt Ns Ar file
Same as
.Ic \*(Gt ,
except if
.Ar file
exists it is appended to instead of being truncated.
Also, the file is opened
in append mode, so writes always go to the end of the file (see
.Xr open 2 ) .
.It \*(Lt Ns Ar file
Standard input is redirected from
.Ar file ,
which is opened for reading.
.It \*(Lt\*(Gt Ns Ar file
Same as
.Ic \*(Lt ,
except the file is opened for reading and writing.
.It \*(Lt\*(Lt Ns Ar marker
After reading the command line containing this kind of redirection (called a
.Dq here document ) ,
the shell copies lines from the command source into a temporary file until a
line matching
.Ar marker
is read.
When the command is executed, standard input is redirected from the
temporary file.
If
.Ar marker
contains no quoted characters, the contents of the temporary file are processed
as if enclosed in double quotes each time the command is executed, so
parameter, command, and arithmetic substitutions are performed, along with
backslash
.Pq Sq \e
escapes for
.Ql $ ,
.Ql \` ,
.Ql \e ,
and
.Ql \enewline ,
but not for
.Ql \&" .
If multiple here documents are used on the same command line, they are saved in
order.
.Pp
If no
.Ar marker
is given, the here document ends at the next
.Ic \*(Lt\*(Lt
and substitution will be performed.
If
.Ar marker
is only a set of either single
.Dq \*(aq\*(aq
or double
.Sq \&""
quotes with nothing in between, the here document ends at the next empty line
and substitution will not be performed.
.It \*(Lt\*(Lt\- Ns Ar marker
Same as
.Ic \*(Lt\*(Lt ,
except leading tabs are stripped from lines in the here document.
.It \*(Lt\*(Lt\*(Lt Ns Ar word
Same as
.Ic \*(Lt\*(Lt ,
except that
.Ar word
.Em is
the here document.
This is called a here string.
.It \*(Lt& Ns Ar fd
Standard input is duplicated from file descriptor
.Ar fd .
.Ar fd
can be a number, indicating the number of an existing file descriptor;
the letter
.Ql p ,
indicating the file descriptor associated with the output of the current
co-process; or the character
.Ql \- ,
indicating standard input is to be closed.
Note that
.Ar fd
is limited to a single digit in most shell implementations.
.It \*(Gt& Ns Ar fd
Same as
.Ic \*(Lt& ,
except the operation is done on standard output.
.It &\*(Gt Ns Ar file
Same as
.Ic \*(Gt Ns Ar file 2\*(Gt&1 .
This is a deprecated (legacy) GNU
.Nm bash
extension supported by
.Nm
which also supports the preceding explicit fd number, for example,
.Ic 3&\*(Gt Ns Ar file
is the same as
.Ic 3\*(Gt Ns Ar file 2\*(Gt&3
in
.Nm
but a syntax error in GNU
.Nm bash .
.It Xo
.No &\*(Gt\*(Ba Ns Ar file ,
.No &\*(Gt\*(Gt Ns Ar file ,
.No &\*(Gt& Ns Ar fd
.Xc
Same as
.Ic \*(Gt\*(Ba Ns Ar file ,
.Ic \*(Gt\*(Gt Ns Ar file ,
or
.Ic \*(Gt& Ns Ar fd ,
followed by
.Ic 2\*(Gt&1 ,
as above.
These are
.Nm
extensions.
.El
.Pp
In any of the above redirections, the file descriptor that is redirected
(i.e. standard input or standard output)
can be explicitly given by preceding the
redirection with a number (portably, only a single digit).
Parameter, command, and arithmetic
substitutions, tilde substitutions, and (if the shell is interactive)
file name generation are all performed on the
.Ar file ,
.Ar marker ,
and
.Ar fd
arguments of redirections.
Note, however, that the results of any file name
generation are only used if a single file is matched; if multiple files match,
the word with the expanded file name generation characters is used.
Note
that in restricted shells, redirections which can create files cannot be used.
.Pp
For simple-commands, redirections may appear anywhere in the command; for
compound-commands
.Po
.Ic if
statements, etc.
.Pc ,
any redirections must appear at the end.
Redirections are processed after
pipelines are created and in the order they are given, so the following
will print an error with a line number prepended to it:
.Pp
.D1 $ cat /foo/bar 2\*(Gt&1 \*(Gt/dev/null \*(Ba pr \-n \-t
.Pp
File descriptors created by I/O redirections are private to the shell.
.Ss Arithmetic expressions
Integer arithmetic expressions can be used with the
.Ic let
command, inside $((..)) expressions, inside array references (e.g.\&
.Ar name Ns Bq Ar expr ) ,
as numeric arguments to the
.Ic test
command, and as the value of an assignment to an integer parameter.
.Em Warning :
This also affects implicit conversion to integer, for example as done by the
.Ic let
command.
.Em Never
use unchecked user input, e.g. from the environment, in arithmetics!
.Pp
Expressions are calculated using signed arithmetic and the
.Vt mksh_ari_t
type (a 32-bit signed integer), unless they begin with a sole
.Sq #
character, in which case they use
.Vt mksh_uari_t
.Po a 32-bit unsigned integer Pc .
.Pp
Expressions may contain alpha-numeric parameter identifiers, array references,
and integer constants and may be combined with the following C operators
(listed and grouped in increasing order of precedence):
.Pp
Unary operators:
.Bd -literal -offset indent
+ \- ! \*(TI ++ \-\-
.Ed
.Pp
Binary operators:
.Bd -literal -offset indent
,
= += \-= *= /= %= \*(Lt\*(Lt\*(Lt= \*(Gt\*(Gt\*(Gt= \*(Lt\*(Lt= \*(Gt\*(Gt= &= \*(ha= \*(Ba=
\*(Ba\*(Ba
&&
\*(Ba
\*(ha
&
== !=
\*(Lt \*(Lt= \*(Gt \*(Gt=
\*(Lt\*(Lt\*(Lt \*(Gt\*(Gt\*(Gt \*(Lt\*(Lt \*(Gt\*(Gt
+ \-
* / %
.Ed
.Pp
Ternary operators:
.Bd -literal -offset indent
?: (precedence is immediately higher than assignment)
.Ed
.Pp
Grouping operators:
.Bd -literal -offset indent
( )
.Ed
.Pp
Integer constants and expressions are calculated using an exactly 32-bit
wide, signed or unsigned, type with silent wraparound on integer overflow.
Integer constants may be specified with arbitrary bases using the notation
.Ar base Ns # Ns Ar number ,
where
.Ar base
is a decimal integer specifying the base, and
.Ar number
is a number in the specified base.
Additionally, base-16 integers may be specified by prefixing them with
.Sq 0x
.Pq case-insensitive
in all forms of arithmetic expressions, except as numeric arguments to the
.Ic test
built-in command.
Prefixing numbers with a sole digit zero
.Pq Sq 0
does not cause interpretation as octal, as that's unsafe to do.
.Pp
As a special
.Nm mksh
extension, numbers to the base of one are treated as either (8-bit
transparent) ASCII or Unicode codepoints, depending on the shell's
.Ic utf8\-mode
flag (current setting).
The
.At
.Nm ksh93
syntax of
.Dq \*(aqx\*(aq
instead of
.Dq 1#x
is also supported.
Note that NUL bytes (integral value of zero) cannot be used.
An unset or empty parameter evaluates to 0 in integer context.
In Unicode mode, raw octets are mapped into the range EF80..EFFF as in
OPTU-8, which is in the PUA and has been assigned by CSUR for this use.
If more than one octet in ASCII mode, or a sequence of more than one
octet not forming a valid and minimal CESU-8 sequence is passed, the
behaviour is undefined (usually, the shell aborts with a parse error,
but rarely, it succeeds, e.g. on the sequence C2 20).
That's why you should always use ASCII mode unless you know that the
input is well-formed UTF-8 in the range of 0000..FFFD if you use this
feature, as opposed to
.Ic read Fl a .
.Pp
The operators are evaluated as follows:
.Bl -tag -width Ds -offset indent
.It unary +
Result is the argument (included for completeness).
.It unary \-
Negation.
.It \&!
Logical NOT;
the result is 1 if argument is zero, 0 if not.
.It \*(TI
Arithmetic (bit-wise) NOT.
.It ++
Increment; must be applied to a parameter (not a literal or other expression).
The parameter is incremented by 1.
When used as a prefix operator, the result
is the incremented value of the parameter; when used as a postfix operator, the
result is the original value of the parameter.
.It \-\-
Similar to
.Ic ++ ,
except the parameter is decremented by 1.
.It \&,
Separates two arithmetic expressions; the left-hand side is evaluated first,
then the right.
The result is the value of the expression on the right-hand side.
.It =
Assignment; the variable on the left is set to the value on the right.
.It Xo
.No += \-= *= /= %= \*(Lt\*(Lt\*(Lt= \*(Gt\*(Gt\*(Gt=
.No \*(Lt\*(Lt= \*(Gt\*(Gt= &= \*(ha= \*(Ba=
.Xc
Assignment operators.
.Sm off
.Ao Ar var Ac Xo
.Aq Ar op
.No = Aq Ar expr
.Xc
.Sm on
is the same as
.Sm off
.Ao Ar var Ac Xo
.No = Aq Ar var
.Aq Ar op
.Aq Ar expr ,
.Xc
.Sm on
with any operator precedence in
.Aq Ar expr
preserved.
For example,
.Dq var1 *= 5 + 3
is the same as specifying
.Dq var1 = var1 * (5 + 3) .
.It \*(Ba\*(Ba
Logical OR;
the result is 1 if either argument is non-zero, 0 if not.
The right argument is evaluated only if the left argument is zero.
.It &&
Logical AND;
the result is 1 if both arguments are non-zero, 0 if not.
The right argument is evaluated only if the left argument is non-zero.
.It \*(Ba
Arithmetic (bit-wise) OR.
.It \*(ha
Arithmetic (bit-wise) XOR
(exclusive-OR).
.It &
Arithmetic (bit-wise) AND.
.It ==
Equal; the result is 1 if both arguments are equal, 0 if not.
.It !=
Not equal; the result is 0 if both arguments are equal, 1 if not.
.It \*(Lt
Less than; the result is 1 if the left argument is less than the right, 0 if
not.
.It \*(Lt= \*(Gt \*(Gt=
Less than or equal, greater than, greater than or equal.
See
.Ic \*(Lt .
.It \*(Lt\*(Lt\*(Lt \*(Gt\*(Gt\*(Gt
Rotate left (right); the result is similar to shift (see
.Ic \*(Lt\*(Lt )
except that the bits shifted out at one end are shifted in
at the other end, instead of zero or sign bits.
.It \*(Lt\*(Lt \*(Gt\*(Gt
Shift left (right); the result is the left argument with its bits shifted left
(right) by the amount given in the right argument.
.It + \- * /
Addition, subtraction, multiplication, and division.
.It %
Remainder; the result is the symmetric remainder of the division of the left
argument by the right.
To get the mathematical modulus of
.Dq a Ic mod No b ,
use the formula
.Do
.Pq a % b + b
.No % b
.Dc .
.It Xo
.Sm off
.Aq Ar arg1 ?
.Aq Ar arg2 :
.Aq Ar arg3
.Sm on
.Xc
If
.Aq Ar arg1
is non-zero, the result is
.Aq Ar arg2 ;
otherwise the result is
.Aq Ar arg3 .
The non-result argument is not evaluated.
.El
.Ss Co-processes
A co-process (which is a pipeline created with the
.Sq \*(Ba&
operator) is an asynchronous process that the shell can both write to (using
.Ic print Fl p )
and read from (using
.Ic read Fl p ) .
The input and output of the co-process can also be manipulated using
.Ic \*(Gt&p
and
.Ic \*(Lt&p
redirections, respectively.
Once a co-process has been started, another can't
be started until the co-process exits, or until the co-process's input has been
redirected using an
.Ic exec Ar n Ns Ic \*(Gt&p
redirection.
If a co-process's input is redirected in this way, the next
co-process to be started will share the output with the first co-process,
unless the output of the initial co-process has been redirected using an
.Ic exec Ar n Ns Ic \*(Lt&p
redirection.
.Pp
Some notes concerning co-processes:
.Bl -bullet
.It
The only way to close the co-process's input (so the co-process reads an
end-of-file) is to redirect the input to a numbered file descriptor and then
close that file descriptor:
.Ic exec 3\*(Gt&p; exec 3\*(Gt&\-
.It
In order for co-processes to share a common output, the shell must keep the
write portion of the output pipe open.
This means that end-of-file will not be
detected until all co-processes sharing the co-process's output have exited
(when they all exit, the shell closes its copy of the pipe).
This can be
avoided by redirecting the output to a numbered file descriptor (as this also
causes the shell to close its copy).
Note that this behaviour is slightly
different from the original Korn shell which closes its copy of the write
portion of the co-process output when the most recently started co-process
(instead of when all sharing co-processes) exits.
.It
.Ic print Fl p
will ignore
.Dv SIGPIPE
signals during writes if the signal is not being trapped or ignored; the same
is true if the co-process input has been duplicated to another file descriptor
and
.Ic print Fl u Ns Ar n
is used.
.El
.Ss Functions
Functions are defined using either Korn shell
.Ic function Ar function-name
syntax or the Bourne/POSIX shell
.Ar function-name Ns \&()
syntax (see below for the difference between the two forms).
Functions are like
.Li .\(hyscripts
(i.e. scripts sourced using the
.Sq \&.
built-in)
in that they are executed in the current environment.
However, unlike
.Li .\(hyscripts ,
shell arguments (i.e. positional parameters $1, $2, etc.)\&
are never visible inside them.
When the shell is determining the location of a command, functions
are searched after special built-in commands, before builtins and the
.Ev PATH
is searched.
.Pp
An existing function may be deleted using
.Ic unset Fl f Ar function-name .
A list of functions can be obtained using
.Ic typeset +f
and the function definitions can be listed using
.Ic typeset Fl f .
The
.Ic autoload
command (which is an alias for
.Ic typeset Fl fu )
may be used to create undefined functions: when an undefined function is
executed, the shell searches the path specified in the
.Ev FPATH
parameter for a file with the same name as the function which, if found, is
read and executed.
If after executing the file the named function is found to
be defined, the function is executed; otherwise, the normal command search is
continued (i.e. the shell searches the regular built-in command table and
.Ev PATH ) .
Note that if a command is not found using
.Ev PATH ,
an attempt is made to autoload a function using
.Ev FPATH
(this is an undocumented feature of the original Korn shell).
.Pp
Functions can have two attributes,
.Dq trace
and
.Dq export ,
which can be set with
.Ic typeset Fl ft
and
.Ic typeset Fl fx ,
respectively.
When a traced function is executed, the shell's
.Ic xtrace
option is turned on for the function's duration.
The
.Dq export
attribute of functions is currently not used.
In the original Korn shell,
exported functions are visible to shell scripts that are executed.
.Pp
Since functions are executed in the current shell environment, parameter
assignments made inside functions are visible after the function completes.
If this is not the desired effect, the
.Ic typeset
command can be used inside a function to create a local parameter.
Note that
.At
.Nm ksh93
uses static scoping (one global scope, one local scope per function)
and allows local variables only on Korn style functions, whereas
.Nm mksh
uses dynamic scoping (nested scopes of varying locality).
Note that special parameters (e.g.\&
.Ic \&$$ , $! )
can't be scoped in this way.
.Pp
The exit status of a function is that of the last command executed in the
function.
A function can be made to finish immediately using the
.Ic return
command; this may also be used to explicitly specify the exit status.
.Pp
Functions defined with the
.Ic function
reserved word are treated differently in the following ways from functions
defined with the
.Ic \&()
notation:
.Bl -bullet
.It
The $0 parameter is set to the name of the function
(Bourne-style functions leave $0 untouched).
.It
Parameter assignments preceding function calls are not kept in the shell
environment (executing Bourne-style functions will keep assignments).
.It
.Ev OPTIND
is saved/reset and restored on entry and exit from the function so
.Ic getopts
can be used properly both inside and outside the function (Bourne-style
functions leave
.Ev OPTIND
untouched, so using
.Ic getopts
inside a function interferes with using
.Ic getopts
outside the function).
.It
Shell options
.Pq Ic set Fl o
have local scope, i.e. changes inside a function are reset upon its exit.
.El
.Pp
In the future, the following differences may also be added:
.Bl -bullet
.It
A separate trap/signal environment will be used during the execution of
functions.
This will mean that traps set inside a function will not affect the
shell's traps and signals that are not ignored in the shell (but may be
trapped) will have their default effect in a function.
.It
The EXIT trap, if set in a function, will be executed after the function
returns.
.El
.Ss Command execution
After evaluation of command-line arguments, redirections, and parameter
assignments, the type of command is determined: a special built-in command,
a function, a normal builtin, or the name of a file to execute found using the
.Ev PATH
parameter.
The checks are made in the above order.
Special built-in commands differ from other commands in that the
.Ev PATH
parameter is not used to find them, an error during their execution can
cause a non-interactive shell to exit, and parameter assignments that are
specified before the command are kept after the command completes.
Regular built-in commands are different only in that the
.Ev PATH
parameter is not used to find them.
.Pp
The original
.Nm ksh
and POSIX differ somewhat in which commands are considered
special or regular.
.Pp
POSIX special built-in utilities:
.Pp
.Ic \&. , \&: , break , continue ,
.Ic eval , exec , exit , export ,
.Ic readonly , return , set , shift ,
.Ic times , trap , unset
.Pp
Additional
.Nm
commands keeping assignments:
.Pp
.Ic builtin , global , source , typeset ,
.Ic wait
.Pp
Builtins that are not special:
.Pp
.Ic [ , alias , bg , bind ,
.Ic cat , cd , command , echo ,
.Ic false , fc , fg , getopts ,
.Ic jobs , kill , let , print ,
.Ic pwd , read , realpath , rename ,
.Ic sleep , suspend , test , true ,
.Ic ulimit , umask , unalias , whence
.Pp
Once the type of command has been determined, any command-line parameter
assignments are performed and exported for the duration of the command.
.Pp
The following describes the special and regular built-in commands and
builtin-like reserved words:
.Pp
.Bl -tag -width false -compact
.It Ic \&. Ar file Op Ar arg ...
This is called the
.Dq dot
command.
Execute the commands in
.Ar file
in the current environment.
The file is searched for in the directories of
.Ev PATH .
If arguments are given, the positional parameters may be used to access them
while
.Ar file
is being executed.
If no arguments are given, the positional parameters are
those of the environment the command is used in.
.Pp
.It Ic \&: Op Ar ...
The null command.
Exit status is set to zero.
.Pp
.It Ic \&[ Ar expression Ic \&]
See
.Ic test .
.Pp
.It Xo Ic alias
.Oo Fl d \*(Ba t Oo Fl r Oc \*(Ba
.Cm +\-x Oc
.Op Fl p
.Op Cm +
.Oo Ar name
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
Without arguments,
.Ic alias
lists all aliases.
For any name without a value, the existing alias is listed.
Any name with a value defines an alias (see
.Sx Aliases
above).
.Pp
When listing aliases, one of two formats is used.
Normally, aliases are listed as
.Ar name Ns = Ns Ar value ,
where
.Ar value
is quoted.
If options were preceded with
.Ql + ,
or a lone
.Ql +
is given on the command line, only
.Ar name
is printed.
.Pp
The
.Fl d
option causes directory aliases which are used in tilde expansion to be
listed or set (see
.Sx Tilde expansion
above).
.Pp
If the
.Fl p
option is used, each alias is prefixed with the string
.Dq alias\ \& .
.Pp
The
.Fl t
option indicates that tracked aliases are to be listed/set (values specified on
the command line are ignored for tracked aliases).
The
.Fl r
option indicates that all tracked aliases are to be reset.
.Pp
The
.Fl x
option sets
.Pq Ic +x No clears
the export attribute of an alias, or, if no names are given, lists the aliases
with the export attribute (exporting an alias has no effect).
.Pp
.It Ic bg Op Ar job ...
Resume the specified stopped job(s) in the background.
If no jobs are specified,
.Ic %+
is assumed.
See
.Sx Job control
below for more information.
.Pp
.It Ic bind Op Fl l
The current bindings are listed.
If the
.Fl l
flag is given,
.Ic bind
instead lists the names of the functions to which keys may be bound.
See
.Sx Emacs editing mode
for more information.
.Pp
.It Xo Ic bind Op Fl m
.Ar string Ns = Ns Op Ar substitute
.Ar ...
.Xc
.It Xo Ic bind
.Ar string Ns = Ns Op Ar editing-command
.Ar ...
.Xc
The specified editing command is bound to the given
.Ar string ,
which should consist of a control character
optionally preceded by one of the two prefix characters
and optionally succeded by a tilde character.
Future input of the
.Ar string
will cause the editing command to be immediately invoked.
If the
.Fl m
flag is given, the specified input
.Ar string
will afterwards be immediately replaced by the given
.Ar substitute
string which may contain editing commands but not other macros.
If a tilde postfix is given, a tilde trailing the one or
two prefices and the control character is ignored, any
other trailing character will be processed afterwards.
.Pp
Control characters may be written using caret notation
i.e. \*(haX represents Ctrl-X.
Note that although only two prefix characters (usually ESC and \*(haX)
are supported, some multi-character sequences can be supported.
.Pp
The following default bindings show how the arrow keys, the home, end and
delete key on a BSD wsvt25, xterm\-xfree86 or GNU screen terminal are bound
(of course some escape sequences won't work out quite this nicely):
.Bd -literal -offset indent
bind \*(aq\*(haX\*(aq=prefix\-2
bind \*(aq\*(ha[[\*(aq=prefix\-2
bind \*(aq\*(haXA\*(aq=up\-history
bind \*(aq\*(haXB\*(aq=down\-history
bind \*(aq\*(haXC\*(aq=forward\-char
bind \*(aq\*(haXD\*(aq=backward\-char
bind \*(aq\*(haX1\*(TI\*(aq=beginning\-of\-line
bind \*(aq\*(haX7\*(TI\*(aq=beginning\-of\-line
bind \*(aq\*(haXH\*(aq=beginning\-of\-line
bind \*(aq\*(haX4\*(TI\*(aq=end\-of\-line
bind \*(aq\*(haX8\*(TI\*(aq=end\-of\-line
bind \*(aq\*(haXF\*(aq=end\-of\-line
bind \*(aq\*(haX3\*(TI\*(aq=delete\-char\-forward
.Ed
.Pp
.It Ic break Op Ar level
Exit the
.Ar level Ns th
inner-most
.Ic for ,
.Ic select ,
.Ic until ,
or
.Ic while
loop.
.Ar level
defaults to 1.
.Pp
.It Xo
.Ic builtin
.Op Fl \-
.Ar command Op Ar arg ...
.Xc
Execute the built-in command
.Ar command .
.Pp
.It Xo
.Ic cat
.Op Fl u
.Op Ar
.Xc
Read files sequentially, in command line order, and write them to
standard output.
If a
.Ar file
is a single dash
.Pq Sq -
or absent, read from standard input.
For direct builtin calls, the
.Tn POSIX
.Fl u
option is supported as a no-op.
For calls from shell, if any options are given, an external
.Xr cat 1
utility is preferred over the builtin.
.Pp
.It Xo
.Ic cd
.Op Fl L
.Op Ar dir
.Xc
.It Xo
.Ic cd
.Fl P Op Fl e
.Op Ar dir
.Xc
.It Xo
.Ic chdir
.Op Fl eLP
.Op Ar dir
.Xc
Set the working directory to
.Ar dir .
If the parameter
.Ev CDPATH
is set, it lists the search path for the directory containing
.Ar dir .
A
.Dv NULL
path means the current directory.
If
.Ar dir
is found in any component of the
.Ev CDPATH
search path other than the
.Dv NULL
path, the name of the new working directory will be written to standard output.
If
.Ar dir
is missing, the home directory
.Ev HOME
is used.
If
.Ar dir
is
.Ql \- ,
the previous working directory is used (see the
.Ev OLDPWD
parameter).
.Pp
If the
.Fl L
option (logical path) is used or if the
.Ic physical
option isn't set (see the
.Ic set
command below), references to
.Sq ..
in
.Ar dir
are relative to the path used to get to the directory.
If the
.Fl P
option (physical path) is used or if the
.Ic physical
option is set,
.Sq ..
is relative to the filesystem directory tree.
The
.Ev PWD
and
.Ev OLDPWD
parameters are updated to reflect the current and old working directory,
respectively.
If the
.Fl e
option is set for physical filesystem traversal, and
.Ev PWD
could not be set, the exit code is 1; greater than 1 if an
error occurred, 0 otherwise.
.Pp
.It Xo
.Ic cd
.Op Fl eLP
.Ar old new
.Xc
.It Xo
.Ic chdir
.Op Fl eLP
.Ar old new
.Xc
The string
.Ar new
is substituted for
.Ar old
in the current directory, and the shell attempts to change to the new
directory.
.Pp
.It Xo
.Ic command
.Op Fl pVv
.Ar cmd
.Op Ar arg ...
.Xc
If neither the
.Fl v
nor
.Fl V
option is given,
.Ar cmd
is executed exactly as if
.Ic command
had not been specified, with two exceptions:
firstly,
.Ar cmd
cannot be a shell function;
and secondly, special built-in commands lose their specialness
(i.e. redirection and utility errors do not cause the shell to
exit, and command assignments are not permanent).
.Pp
If the
.Fl p
option is given, a default search path is used instead of the current value of
.Ev PATH ,
the actual value of which is system dependent.
.Pp
If the
.Fl v
option is given, instead of executing
.Ar cmd ,
information about what would be executed is given (and the same is done for
.Ar arg ... ) .
For builtins, functions and keywords, their names are simply printed;
for aliases, a command that defines them is printed;
for utilities found by searching the
.Ev PATH
parameter, the full path of the command is printed.
If no command is found
(i.e. the path search fails), nothing is printed and
.Ic command
exits with a non-zero status.
The
.Fl V
option is like the
.Fl v
option, except it is more verbose.
.Pp
.It Ic continue Op Ar level
Jumps to the beginning of the
.Ar level Ns th
inner-most
.Ic for ,
.Ic select ,
.Ic until ,
or
.Ic while
loop.
.Ar level
defaults to 1.
.Pp
.It Xo
.Ic echo
.Op Fl Een
.Op Ar arg ...
.Xc
.Em Warning:
this utility is not portable; use the Korn shell builtin
.Ic print
instead.
.Pp
Prints its arguments (separated by spaces) followed by a newline, to the
standard output.
The newline is suppressed if any of the arguments contain the
backslash sequence
.Ql \ec .
See the
.Ic print
command below for a list of other backslash sequences that are recognised.
.Pp
The options are provided for compatibility with
.Bx
shell scripts.
The
.Fl n
option suppresses the trailing newline,
.Fl e
enables backslash interpretation (a no-op, since this is normally done), and
.Fl E
suppresses backslash interpretation.
.Pp
If the
.Ic posix
or
.Ic sh
option is set or this is a direct builtin call, only the first argument
is treated as an option, and only if it is exactly
.Dq Fl n .
Backslash interpretation is disabled.
.Pp
.It Ic eval Ar command ...
The arguments are concatenated (with spaces between them) to form a single
string which the shell then parses and executes in the current environment.
.Pp
.It Xo
.Ic exec
.Op Fl a Ar argv0
.Op Fl c
.Op Ar command Op Ar arg ...
.Xc
The command is executed without forking, replacing the shell process.
This is currently absolute, i.e.\&
.Ic exec
never returns, even if the
.Ar command
is not found.
The
.Fl a
option permits setting a different
.Li argv[0]
value, and
.Fl c
clears the environment before executing the child process, except for the
.Ev _
variable and direct assignments.
.Pp
If no command is given except for I/O redirection, the I/O redirection is
permanent and the shell is
not replaced.
Any file descriptors greater than 2 which are opened or
.Xr dup 2 Ns 'd
in this way are not made available to other executed commands (i.e. commands
that are not built-in to the shell).
Note that the Bourne shell differs here;
it does pass these file descriptors on.
.Pp
.It Ic exit Op Ar status
The shell exits with the specified exit status.
If
.Ar status
is not specified, the exit status is the current value of the
.Ic $?\&
parameter.
.Pp
.It Xo
.Ic export
.Op Fl p
.Op Ar parameter Ns Op = Ns Ar value
.Xc
Sets the export attribute of the named parameters.
Exported parameters are passed in the environment to executed commands.
If values are specified, the named parameters are also assigned.
.Pp
If no parameters are specified, all parameters with the export attribute
set are printed one per line; either their names, or, if a
.Ql \-
with no option letter is specified, name=value pairs, or, with
.Fl p ,
.Ic export
commands suitable for re-entry.
.Pp
.It Ic false
A command that exits with a non-zero status.
.Pp
.It Xo
.Ic fc
.Oo Fl e Ar editor \*(Ba
.Fl l Op Fl n Oc
.Op Fl r
.Op Ar first Op Ar last
.Xc
.Ar first
and
.Ar last
select commands from the history.
Commands can be selected by history number
(negative numbers go backwards from the current, most recent, line)
or a string specifying the most recent command starting with that string.
The
.Fl l
option lists the command on standard output, and
.Fl n
inhibits the default command numbers.
The
.Fl r
option reverses the order of the list.
Without
.Fl l ,
the selected commands are edited by the editor specified with the
.Fl e
option, or if no
.Fl e
is specified, the editor specified by the
.Ev FCEDIT
parameter (if this parameter is not set,
.Pa /bin/ed
is used), and then executed by the shell.
.Pp
.It Xo
.Ic fc
.Cm \-e \- \*(Ba Fl s
.Op Fl g
.Op Ar old Ns = Ns Ar new
.Op Ar prefix
.Xc
Re-execute the selected command (the previous command by default) after
performing the optional substitution of
.Ar old
with
.Ar new .
If
.Fl g
is specified, all occurrences of
.Ar old
are replaced with
.Ar new .
The meaning of
.Cm \-e \-
and
.Fl s
is identical: re-execute the selected command without invoking an editor.
This command is usually accessed with the predefined:
.Ic alias r=\*(aqfc \-e \-\*(aq
.Pp
.It Ic fg Op Ar job ...
Resume the specified job(s) in the foreground.
If no jobs are specified,
.Ic %+
is assumed.
See
.Sx Job control
below for more information.
.Pp
.It Xo
.Ic getopts
.Ar optstring name
.Op Ar arg ...
.Xc
Used by shell procedures to parse the specified arguments (or positional
parameters, if no arguments are given) and to check for legal options.
.Ar optstring
contains the option letters that
.Ic getopts
is to recognise.
If a letter is followed by a colon, the option is expected to
have an argument.
Options that do not take arguments may be grouped in a single argument.
If an option takes an argument and the option character is not the
last character of the argument it is found in, the remainder of the argument is
taken to be the option's argument; otherwise, the next argument is the option's
argument.
.Pp
Each time
.Ic getopts
is invoked, it places the next option in the shell parameter
.Ar name
and the index of the argument to be processed by the next call to
.Ic getopts
in the shell parameter
.Ev OPTIND .
If the option was introduced with a
.Ql + ,
the option placed in
.Ar name
is prefixed with a
.Ql + .
When an option requires an argument,
.Ic getopts
places it in the shell parameter
.Ev OPTARG .
.Pp
When an illegal option or a missing option argument is encountered, a question
mark or a colon is placed in
.Ar name
(indicating an illegal option or missing argument, respectively) and
.Ev OPTARG
is set to the option character that caused the problem.
Furthermore, if
.Ar optstring
does not begin with a colon, a question mark is placed in
.Ar name ,
.Ev OPTARG
is unset, and an error message is printed to standard error.
.Pp
When the end of the options is encountered,
.Ic getopts
exits with a non-zero exit status.
Options end at the first (non-option
argument) argument that does not start with a
.Ql \- ,
or when a
.Ql \-\-
argument is encountered.
.Pp
Option parsing can be reset by setting
.Ev OPTIND
to 1 (this is done automatically whenever the shell or a shell procedure is
invoked).
.Pp
Warning: Changing the value of the shell parameter
.Ev OPTIND
to a value other than 1, or parsing different sets of arguments without
resetting
.Ev OPTIND ,
may lead to unexpected results.
.Pp
.It global Ar ...
See
.Ic typeset .
.Pp
.It Xo
.Ic hash
.Op Fl r
.Op Ar name ...
.Xc
Without arguments, any hashed executable command pathnames are listed.
The
.Fl r
option causes all hashed commands to be removed from the hash table.
Each
.Ar name
is searched as if it were a command name and added to the hash table if it is
an executable command.
.Pp
.It Xo
.Ic jobs
.Op Fl lnp
.Op Ar job ...
.Xc
Display information about the specified job(s); if no jobs are specified, all
jobs are displayed.
The
.Fl n
option causes information to be displayed only for jobs that have changed
state since the last notification.
If the
.Fl l
option is used, the process ID of each process in a job is also listed.
The
.Fl p
option causes only the process group of each job to be printed.
See
.Sx Job control
below for the format of
.Ar job
and the displayed job.
.Pp
.It Xo
.Ic kill
.Oo Fl s Ar signame \*(Ba
.No \- Ns Ar signum \*(Ba
.No \- Ns Ar signame Oc
.No { Ar job \*(Ba pid \*(Ba pgrp No }
.Ar ...
.Xc
Send the specified signal to the specified jobs, process IDs, or process
groups.
If no signal is specified, the
.Dv TERM
signal is sent.
If a job is specified, the signal is sent to the job's process group.
See
.Sx Job control
below for the format of
.Ar job .
.Pp
.It Xo
.Ic kill
.Fl l
.Op Ar exit-status ...
.Xc
Print the signal name corresponding to
.Ar exit-status .
If no arguments are specified, a list of all the signals, their numbers, and
a short description of them are printed.
.Pp
.It Ic let Op Ar expression ...
Each expression is evaluated (see
.Sx Arithmetic expressions
above).
If all expressions are successfully evaluated, the exit status is 0 (1)
if the last expression evaluated to non-zero (zero).
If an error occurs during
the parsing or evaluation of an expression, the exit status is greater than 1.
Since expressions may need to be quoted,
.No \&(( Ar expr No ))
is syntactic sugar for
.No "{ let '" Ns Ar expr Ns "'; }" .
.Pp
.It Ic let]
Internally used alias for
.Ic let .
.Pp
.It Xo
.Ic mknod
.Op Fl m Ar mode
.Ar name
.Cm b\*(Bac
.Ar major minor
.Xc
.It Xo
.Ic mknod
.Op Fl m Ar mode
.Ar name
.Cm p
.Xc
Create a device special file.
The file type may be
.Cm b
(block type device),
.Cm c
(character type device),
or
.Cm p
.Pq named pipe , Tn FIFO .
The file created may be modified according to its
.Ar mode
(via the
.Fl m
option),
.Ar major
(major device number),
and
.Ar minor
(minor device number).
This is not normally part of
.Nm mksh ;
however, distributors may have added this as builtin as a speed hack.
.Pp
.It Xo
.Ic print
.Oo Fl nprsu Ns Oo Ar n Oc \*(Ba
.Fl R Op Fl en Oc
.Op Ar argument ...
.Xc
.Ic print
prints its arguments on the standard output, separated by spaces and
terminated with a newline.
The
.Fl n
option suppresses the newline.
By default, certain C escapes are translated.
These include these mentioned in
.Sx Backslash expansion
above, as well as
.Ql \ec ,
which is equivalent to using the
.Fl n
option.
Backslash expansion may be inhibited with the
.Fl r
option.
The
.Fl s
option prints to the history file instead of standard output; the
.Fl u
option prints to file descriptor
.Ar n
.Po
.Ar n
defaults to 1 if omitted
.Pc ;
and the
.Fl p
option prints to the co-process (see
.Sx Co-processes
above).
.Pp
The
.Fl R
option is used to emulate, to some degree, the
.Bx
.Xr echo 1
command which does not process
.Ql \e
sequences unless the
.Fl e
option is given.
As above, the
.Fl n
option suppresses the trailing newline.
.Pp
.It Ic printf Ar format Op Ar arguments ...
Formatted output.
Approximately the same as the
.Xr printf 1 ,
utility, except it uses the same
.Sx Backslash expansion
and I/O code and does not handle floating point as the rest of
.Nm mksh .
An external utility is preferred over the builtin.
This is not normally part of
.Nm mksh ;
however, distributors may have added this as builtin as a speed hack.
Do not use in new code.
.Pp
.It Ic pwd Op Fl LP
Print the present working directory.
If the
.Fl L
option is used or if the
.Ic physical
option isn't set (see the
.Ic set
command below), the logical path is printed (i.e. the path used to
.Ic cd
to the current directory).
If the
.Fl P
option (physical path) is used or if the
.Ic physical
option is set, the path determined from the filesystem (by following
.Sq ..
directories to the root directory) is printed.
.Pp
.It Xo
.Ic read
.Op Fl A \*(Ba Fl a
.Op Fl d Ar x
.Oo Fl N Ar z \*(Ba
.Fl n Ar z Oc
.Oo Fl p \*(Ba
.Fl u Ns Op Ar n
.Oc Op Fl t Ar n
.Op Fl rs
.Op Ar p ...
.Xc
Reads a line of input, separates the input into fields using the
.Ev IFS
parameter (see
.Sx Substitution
above), and assigns each field to the specified parameters
.Ar p .
If no parameters are specified, the
.Ev REPLY
parameter is used to store the result.
With the
.Fl A
and
.Fl a
options, only no or one parameter is accepted.
If there are more parameters than fields, the extra parameters are set to
the empty string or 0; if there are more fields than parameters, the last
parameter is assigned the remaining fields (including the word separators).
.Pp
The options are as follows:
.Bl -tag -width XuXnX
.It Fl A
Store the result into the parameter
.Ar p
(or
.Ev REPLY )
as array of words.
.It Fl a
Store the result without word splitting into the parameter
.Ar p
(or
.Ev REPLY )
as array of characters (wide characters if the
.Ic utf8\-mode
option is enacted, octets otherwise); the codepoints are
encoded as decimal numbers by default.
.It Fl d Ar x
Use the first byte of
.Ar x ,
.Dv NUL
if empty, instead of the ASCII newline character as input line delimiter.
.It Fl N Ar z
Instead of reading till end-of-line, read exactly
.Ar z
bytes.
If EOF or a timeout occurs, a partial read is returned with exit status 1.
.It Fl n Ar z
Instead of reading till end-of-line, read up to
.Ar z
bytes but return as soon as any bytes are read, e.g.\& from a
slow terminal device, or if EOF or a timeout occurs.
.It Fl p
Read from the currently active co-process, see
.Sx Co-processes
above for details on this.
.It Fl u Ns Op Ar n
Read from the file descriptor
.Ar n
(defaults to 0, i.e.\& standard input).
The argument must immediately follow the option character.
.It Fl t Ar n
Interrupt reading after
.Ar n
seconds (specified as positive decimal value with an optional fractional part).
The exit status of
.Nm read
is 1 if the timeout occurred, but partial reads may still be returned.
.It Fl r
Normally, the ASCII backslash character escapes the special
meaning of the following character and is stripped from the input;
.Ic read
does not stop when encountering a backslash-newline sequence and
does not store that newline in the result.
This option enables raw mode, in which backslashes are not processed.
.It Fl s
The input line is saved to the history.
.El
.Pp
If the input is a terminal, both the
.Fl N
and
.Fl n
options set it into raw mode;
they read an entire file if \-1 is passed as
.Ar z
argument.
.Pp
The first parameter may have a question mark and a string appended to it, in
which case the string is used as a prompt (printed to standard error before
any input is read) if the input is a
.Xr tty 4
(e.g.\&
.Ic read nfoo?\*(aqnumber of foos: \*(aq ) .
.Pp
If no input is read or a timeout occurred,
.Ic read
exits with a non-zero status.
.Pp
Another handy set of tricks:
If
.Ic read
is run in a loop such as
.Ic while read foo; do ...; done
then leading whitespace will be removed (IFS) and backslashes processed.
You might want to use
.Ic while IFS= read \-r foo; do ...; done
for pristine I/O.
Similarily, when using the
.Fl a
option, use of the
.Fl r
option might be prudent; the same applies for:
.Bd -literal -offset indent
find . \-type f \-print0 \*(Ba& \e
    while IFS= read \-d \*(aq\*(aq \-pr filename; do
	print \-r \-\- "found \*(Lt${filename#./}\*(Gt"
done
.Ed
.Pp
The inner loop will be executed in a subshell and variable changes
cannot be propagated if executed in a pipeline:
.Bd -literal -offset indent
bar \*(Ba baz \*(Ba while read foo; do ...; done
.Ed
.Pp
Use co-processes instead:
.Bd -literal -offset indent
bar \*(Ba baz \*(Ba&
while read \-p foo; do ...; done
exec 3\*(Gt&p; exec 3\*(Gt&\-
.Ed
.Pp
.It Xo
.Ic readonly
.Op Fl p
.Oo Ar parameter
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
Sets the read-only attribute of the named parameters.
If values are given,
parameters are set to them before setting the attribute.
Once a parameter is
made read-only, it cannot be unset and its value cannot be changed.
.Pp
If no parameters are specified, the names of all parameters with the read-only
attribute are printed one per line, unless the
.Fl p
option is used, in which case
.Ic readonly
commands defining all read-only parameters, including their values, are
printed.
.Pp
.It Xo
.Ic realpath
.Op Fl \-
.Ar name
.Xc
Prints the resolved absolute pathname corresponding to
.Ar name .
If
.Ar name
ends with a slash
.Pq Sq / ,
it's also checked for existence and whether it is a directory; otherwise,
.Ic realpath
returns 0 if the pathname either exists or can be created immediately,
i.e. all but the last component exist and are directories.
.Pp
.It Xo
.Ic rename
.Op Fl \-
.Ar from to
.Xc
Renames the file
.Ar from
to
.Ar to .
Both must be complete pathnames and on the same device.
This builtin is intended for emergency situations where
.Pa /bin/mv
becomes unusable, and directly calls
.Xr rename 2 .
.Pp
.It Ic return Op Ar status
Returns from a function or
.Ic .\&
script, with exit status
.Ar status .
If no
.Ar status
is given, the exit status of the last executed command is used.
If used outside of a function or
.Ic .\&
script, it has the same effect as
.Ic exit .
Note that
.Nm
treats both profile and
.Ev ENV
files as
.Ic .\&
scripts, while the original Korn shell only treats profiles as
.Ic .\&
scripts.
.Pp
.It Xo
.Ic set Op Ic +\-abCefhiklmnprsUuvXx
.Op Ic +\-o Ar option
.Op Ic +\-A Ar name
.Op Fl \-
.Op Ar arg ...
.Xc
The
.Ic set
command can be used to set
.Pq Ic \-
or clear
.Pq Ic +
shell options, set the positional parameters, or set an array parameter.
Options can be changed using the
.Cm +\-o Ar option
syntax, where
.Ar option
is the long name of an option, or using the
.Cm +\- Ns Ar letter
syntax, where
.Ar letter
is the option's single letter name (not all options have a single letter name).
The following table lists both option letters (if they exist) and long names
along with a description of what the option does:
.Bl -tag -width 3n
.It Fl A Ar name
Sets the elements of the array parameter
.Ar name
to
.Ar arg ...
If
.Fl A
is used, the array is reset (i.e. emptied) first; if
.Ic +A
is used, the first N elements are set (where N is the number of arguments);
the rest are left untouched.
.Pp
An alternative syntax for the command
.Ic set \-A foo \-\- a b c
which is compatible to
.Tn GNU
.Nm bash
and also supported by
.At
.Nm ksh93
is:
.Ic foo=(a b c); foo+=(d e)
.It Fl a \*(Ba Fl o Ic allexport
All new parameters are created with the export attribute.
.It Fl b \*(Ba Fl o Ic notify
Print job notification messages asynchronously, instead of just before the
prompt.
Only used if job control is enabled
.Pq Fl m .
.It Fl C \*(Ba Fl o Ic noclobber
Prevent \*(Gt redirection from overwriting existing files.
Instead, \*(Gt\*(Ba must be used to force an overwrite.
Note that this is not safe to use for creation of temporary files or
lockfiles due to a TOCTOU in a check allowing one to redirect output to
.Pa /dev/null
or other device files even in
.Ic noclobber
mode.
.It Fl e \*(Ba Fl o Ic errexit
Exit (after executing the
.Dv ERR
trap) as soon as an error occurs or a command fails (i.e. exits with a
non-zero status).
This does not apply to commands whose exit status is
explicitly tested by a shell construct such as
.Ic if ,
.Ic until ,
.Ic while ,
or
.Ic !\&
statements.
For
.Ic &&
or
.Ic \*(Ba\*(Ba ,
only the status of the last command is tested.
.It Fl f \*(Ba Fl o Ic noglob
Do not expand file name patterns.
.It Fl h \*(Ba Fl o Ic trackall
Create tracked aliases for all executed commands (see
.Sx Aliases
above).
Enabled by default for non-interactive shells.
.It Fl i \*(Ba Fl o Ic interactive
The shell is an interactive shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
.It Fl k \*(Ba Fl o Ic keyword
Parameter assignments are recognised anywhere in a command.
.It Fl l \*(Ba Fl o Ic login
The shell is a login shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
.It Fl m \*(Ba Fl o Ic monitor
Enable job control (default for interactive shells).
.It Fl n \*(Ba Fl o Ic noexec
Do not execute any commands.
Useful for checking the syntax of scripts
(ignored if interactive).
.It Fl p \*(Ba Fl o Ic privileged
The shell is a privileged shell.
It is set automatically if, when the shell starts,
the real UID or GID does not match
the effective UID (EUID) or GID (EGID), respectively.
See above for a description of what this means.
.It Fl r \*(Ba Fl o Ic restricted
The shell is a restricted shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
.It Fl s \*(Ba Fl o Ic stdin
If used when the shell is invoked, commands are read from standard input.
Set automatically if the shell is invoked with no arguments.
.Pp
When
.Fl s
is used with the
.Ic set
command it causes the specified arguments to be sorted before assigning them to
the positional parameters (or to array
.Ar name ,
if
.Fl A
is used).
.It Fl U \*(Ba Fl o Ic utf8\-mode
Enable UTF-8 support in the
.Sx Emacs editing mode
and internal string handling functions.
This flag is disabled by default, but can be enabled by setting it on the
shell command line; is enabled automatically for interactive shells if
requested at compile time, your system supports
.Fn setlocale LC_CTYPE \&""
and optionally
.Fn nl_langinfo CODESET ,
or the
.Ev LC_ALL ,
.Ev LC_CTYPE ,
or
.Ev LANG
environment variables,
and at least one of these returns something that matches
.Dq UTF\-8
or
.Dq utf8
case-insensitively; for direct builtin calls depending on the
aforementioned environment variables; or for stdin or scripts,
if the input begins with a UTF-8 Byte Order Mark.
.Pp
In near future, locale tracking will be implemented, which means that
.Ic set Fl +U
is changed whenever one of the
.Tn POSIX
locale-related environment variables changes.
.It Fl u \*(Ba Fl o Ic nounset
Referencing of an unset parameter, other than
.Dq $@
or
.Dq $* ,
is treated as an error, unless one of the
.Ql \- ,
.Ql + ,
or
.Ql =
modifiers is used.
.It Fl v \*(Ba Fl o Ic verbose
Write shell input to standard error as it is read.
.It Fl X \*(Ba Fl o Ic markdirs
Mark directories with a trailing
.Ql /
during file name generation.
.It Fl x \*(Ba Fl o Ic xtrace
Print command trees when they are executed, preceded by
the value of
.Ev PS4 .
.It Fl o Ic bgnice
Background jobs are run with lower priority.
.It Fl o Ic braceexpand
Enable brace expansion (a.k.a. alternation).
This is enabled by default.
If disabled, tilde expansion after an equals sign is disabled as a side effect.
.It Fl o Ic emacs
Enable BRL emacs-like command-line editing (interactive shells only); see
.Sx Emacs editing mode .
.It Fl o Ic gmacs
Enable gmacs-like command-line editing (interactive shells only).
Currently identical to emacs editing except that transpose\-chars (\*(haT) acts
slightly differently.
.It Fl o Ic ignoreeof
The shell will not (easily) exit when end-of-file is read;
.Ic exit
must be used.
To avoid infinite loops, the shell will exit if
.Dv EOF
is read 13 times in a row.
.It Fl o Ic inherit\-xtrace
Do not reset
.Fl o Ic xtrace
upon entering functions.
This is enabled by default.
.It Fl o Ic nohup
Do not kill running jobs with a
.Dv SIGHUP
signal when a login shell exits.
Currently set by default, but this may
change in the future to be compatible with
.At
.Nm ksh ,
which
doesn't have this option, but does send the
.Dv SIGHUP
signal.
.It Fl o Ic nolog
No effect.
In the original Korn shell, this prevents function definitions from
being stored in the history file.
.It Fl o Ic physical
Causes the
.Ic cd
and
.Ic pwd
commands to use
.Dq physical
(i.e. the filesystem's)
.Sq ..
directories instead of
.Dq logical
directories (i.e. the shell handles
.Sq .. ,
which allows the user to be oblivious of symbolic links to directories).
Clear by default.
Note that setting this option does not affect the current value of the
.Ev PWD
parameter; only the
.Ic cd
command changes
.Ev PWD .
See the
.Ic cd
and
.Ic pwd
commands above for more details.
.It Fl o Ic pipefail
Make the exit status of a pipeline (before logically complementing) the
rightmost non-zero errorlevel, or zero if all commands exited with zero.
.It Fl o Ic posix
Behave closer to the standards
(see
.Sx POSIX mode
for details).
Automatically enabled if the basename of the shell invocation begins with
.Dq sh
and this autodetection feature is compiled in
.Pq not in MirBSD .
As a side effect, setting this flag turns off
.Ic braceexpand
mode, which can be turned back on manually, and
.Ic sh
mode (unless both are enabled at the same time).
.It Fl o Ic sh
Enable
.Pa /bin/sh
.Pq kludge
mode (see
.Sx SH mode ) .
Automatically enabled if the basename of the shell invocation begins with
.Dq sh
and this autodetection feature is compiled in
.Pq not in MirBSD .
As a side effect, setting this flag turns off
.Ic braceexpand
mode, which can be turned back on manually, and
.Ic posix
mode (unless both are enabled at the same time).
.It Fl o Ic vi
Enable
.Xr vi 1 Ns -like
command-line editing (interactive shells only).
See
.Sx Vi editing mode
for documentation and limitations.
.It Fl o Ic vi\-esccomplete
In vi command-line editing, do command and file name completion when escape
(\*(ha[) is entered in command mode.
.It Fl o Ic vi\-tabcomplete
In vi command-line editing, do command and file name completion when tab (\*(haI)
is entered in insert mode.
This is the default.
.It Fl o Ic viraw
No effect.
In the original Korn shell, unless
.Ic viraw
was set, the vi command-line mode would let the
.Xr tty 4
driver do the work until ESC (\*(ha[) was entered.
.Nm
is always in viraw mode.
.El
.Pp
These options can also be used upon invocation of the shell.
The current set of
options (with single letter names) can be found in the parameter
.Sq $\- .
.Ic set Fl o
with no option name will list all the options and whether each is on or off;
.Ic set +o
will print the long names of all options that are currently on.
.Pp
Remaining arguments, if any, are positional parameters and are assigned, in
order, to the positional parameters (i.e. $1, $2, etc.).
If options end with
.Ql \-\-
and there are no remaining arguments, all positional parameters are cleared.
If no options or arguments are given, the values of all names are printed.
For unknown historical reasons, a lone
.Ql \-
option is treated specially \*(en it clears both the
.Fl v
and
.Fl x
options.
.Pp
.It Ic shift Op Ar number
The positional parameters
.Ar number Ns +1 ,
.Ar number Ns +2 ,
etc. are renamed to
.Sq 1 ,
.Sq 2 ,
etc.
.Ar number
defaults to 1.
.Pp
.It Ic sleep Ar seconds
Suspends execution for a minimum of the
.Ar seconds
specified as positive decimal value with an optional fractional part.
Signal delivery may continue execution earlier.
.Pp
.It Ic source Ar file Op Ar arg ...
Like
.Ic \&. Po Do dot Dc Pc ,
except that the current working directory is appended to the
search path (GNU
.Nm bash
extension).
.Pp
.It Ic suspend
Stops the shell as if it had received the suspend character from
the terminal.
It is not possible to suspend a login shell unless the parent process
is a member of the same terminal session but is a member of a different
process group.
As a general rule, if the shell was started by another shell or via
.Xr su 1 ,
it can be suspended.
.Pp
.It Ic test Ar expression
.It Ic \&[ Ar expression Ic \&]
.Ic test
evaluates the
.Ar expression
and returns zero status if true, 1 if false, or greater than 1 if there
was an error.
It is normally used as the condition command of
.Ic if
and
.Ic while
statements.
Symbolic links are followed for all
.Ar file
expressions except
.Fl h
and
.Fl L .
.Pp
The following basic expressions are available:
.Bl -tag -width 17n
.It Fl a Ar file
.Ar file
exists.
.It Fl b Ar file
.Ar file
is a block special device.
.It Fl c Ar file
.Ar file
is a character special device.
.It Fl d Ar file
.Ar file
is a directory.
.It Fl e Ar file
.Ar file
exists.
.It Fl f Ar file
.Ar file
is a regular file.
.It Fl G Ar file
.Ar file Ns 's
group is the shell's effective group ID.
.It Fl g Ar file
.Ar file Ns 's
mode has the setgid bit set.
.It Fl H Ar file
.Ar file
is a context dependent directory (only useful on HP-UX).
.It Fl h Ar file
.Ar file
is a symbolic link.
.It Fl k Ar file
.Ar file Ns 's
mode has the
.Xr sticky 8
bit set.
.It Fl L Ar file
.Ar file
is a symbolic link.
.It Fl O Ar file
.Ar file Ns 's
owner is the shell's effective user ID.
.It Fl o Ar option
Shell
.Ar option
is set (see the
.Ic set
command above for a list of options).
As a non-standard extension, if the option starts with a
.Ql \&! ,
the test is negated; the test always fails if
.Ar option
doesn't exist (so [ \-o foo \-o \-o !foo ] returns true if and only if option
.Ar foo
exists).
The same can be achieved with [ \-o ?foo ] like in
.At
.Nm ksh93 .
.Ar option
can also be the short flag led by either
.Ql \-
or
.Ql +
.Pq no logical negation ,
for example
.Ql \-x
or
.Ql +x
instead of
.Ql xtrace .
.It Fl p Ar file
.Ar file
is a named pipe
.Pq Tn FIFO .
.It Fl r Ar file
.Ar file
exists and is readable.
.It Fl S Ar file
.Ar file
is a
.Xr unix 4 Ns -domain
socket.
.It Fl s Ar file
.Ar file
is not empty.
.It Fl t Ar fd
File descriptor
.Ar fd
is a
.Xr tty 4
device.
.It Fl u Ar file
.Ar file Ns 's
mode has the setuid bit set.
.It Fl w Ar file
.Ar file
exists and is writable.
.It Fl x Ar file
.Ar file
exists and is executable.
.It Ar file1 Fl nt Ar file2
.Ar file1
is newer than
.Ar file2
or
.Ar file1
exists and
.Ar file2
does not.
.It Ar file1 Fl ot Ar file2
.Ar file1
is older than
.Ar file2
or
.Ar file2
exists and
.Ar file1
does not.
.It Ar file1 Fl ef Ar file2
.Ar file1
is the same file as
.Ar file2 .
.It Ar string
.Ar string
has non-zero length.
.It Fl n Ar string
.Ar string
is not empty.
.It Fl z Ar string
.Ar string
is empty.
.It Ar string No = Ar string
Strings are equal.
.It Ar string No == Ar string
Strings are equal.
.It Ar string No \*(Gt Ar string
First string operand is greater than second string operand.
.It Ar string No \*(Lt Ar string
First string operand is less than second string operand.
.It Ar string No != Ar string
Strings are not equal.
.It Ar number Fl eq Ar number
Numbers compare equal.
.It Ar number Fl ne Ar number
Numbers compare not equal.
.It Ar number Fl ge Ar number
Numbers compare greater than or equal.
.It Ar number Fl gt Ar number
Numbers compare greater than.
.It Ar number Fl le Ar number
Numbers compare less than or equal.
.It Ar number Fl \&lt Ar number
Numbers compare less than.
.El
.Pp
The above basic expressions, in which unary operators have precedence over
binary operators, may be combined with the following operators (listed in
increasing order of precedence):
.Bd -literal -offset indent
expr \-o expr		Logical OR.
expr \-a expr		Logical AND.
! expr			Logical NOT.
( expr )		Grouping.
.Ed
.Pp
Note that a number actually may be an arithmetic expression, such as
a mathematical term or the name of an integer variable:
.Bd -literal -offset indent
x=1; [ "x" \-eq 1 ]	evaluates to true
.Ed
.Pp
Note that some special rules are applied (courtesy of
.Px
) if the number of arguments to
.Ic test
or inside the brackets
.Ic \&[ ... \&]
is less than five: if leading
.Ql \&!
arguments can be stripped such that only one to three arguments remain,
then the lowered comparison is executed; (thanks to XSI) parentheses
.Ic \e( ... \e)
lower four- and three-argument forms to two- and one-argument forms,
respectively; three-argument forms ultimately prefer binary operations,
followed by negation and parenthesis lowering; two- and four-argument forms
prefer negation followed by parenthesis; the one-argument form always implies
.Fl n .
.Pp
.Sy Note :
A common mistake is to use
.Dq if \&[ $foo = bar \&]
which fails if parameter
.Dq foo
is
.Dv NULL
or unset, if it has embedded spaces (i.e.\&
.Ev IFS
octets), or if it is a unary operator like
.Sq \&!
or
.Sq Fl n .
Use tests like
.Dq if \&[ x\&"$foo\&" = x"bar" \&]
instead, or the double-bracket operator
.Dq if \&[[ $foo = bar \&]]
or, to avoid pattern matching (see
.Ic \&[[
above):
.Dq if \&[[ $foo = \&"$bar" \&]]
.Pp
The
.Ic \&[[ ... ]]
construct is not only more secure to use but also often faster.
.Pp
.It Xo
.Ic time
.Op Fl p
.Op Ar pipeline
.Xc
If a
.Ar pipeline
is given, the times used to execute the pipeline are reported.
If no pipeline
is given, then the user and system time used by the shell itself, and all the
commands it has run since it was started, are reported.
The times reported are the real time (elapsed time from start to finish),
the user CPU time (time spent running in user mode), and the system CPU time
(time spent running in kernel mode).
Times are reported to standard error; the format of the output is:
.Pp
.Dl "0m0.00s real     0m0.00s user     0m0.00s system"
.Pp
If the
.Fl p
option is given the output is slightly longer:
.Bd -literal -offset indent
real     0.00
user     0.00
sys      0.00
.Ed
.Pp
It is an error to specify the
.Fl p
option unless
.Ar pipeline
is a simple command.
.Pp
Simple redirections of standard error do not affect the output of the
.Ic time
command:
.Pp
.Dl $ time sleep 1 2\*(Gtafile
.Dl $ { time sleep 1; } 2\*(Gtafile
.Pp
Times for the first command do not go to
.Dq afile ,
but those of the second command do.
.Pp
.It Ic times
Print the accumulated user and system times used both by the shell
and by processes that the shell started which have exited.
The format of the output is:
.Bd -literal -offset indent
0m0.00s 0m0.00s
0m0.00s 0m0.00s
.Ed
.Pp
.It Ic trap Ar n Op Ar signal ...
If the first operand is a decimal unsigned integer, this resets all
specified signals to the default action, i.e. is the same as calling
.Ic trap
with a minus sign
.Pq Sq \-
as
.Ar handler ,
followed by the arguments
.Pq Ar n Op Ar signal ... ,
all of which are treated as signals.
.Pp
.It Ic trap Op Ar handler signal ...
Sets a trap handler that is to be executed when any of the specified
.Ar signal Ns s
are received.
.Ar handler
is either an empty string, indicating the signals are to be ignored,
a minus sign
.Pq Sq \- ,
indicating that the default action is to be taken for the signals
.Pq see Xr signal 3 ,
or a string containing shell commands to be executed at the first opportunity
(i.e. when the current command completes, or before printing the next
.Ev PS1
prompt) after receipt of one of the signals.
.Ar signal
is the name of a signal
.Pq e.g.\& Dv PIPE or Dv ALRM
or the number of the signal (see the
.Ic kill Fl l
command above).
.Pp
There are two special signals:
.Dv EXIT
.Pq also known as 0 ,
which is executed when the shell is about to exit, and
.Dv ERR ,
which is executed after an error occurs; an error is something
that would cause the shell to exit if the
.Ic set Fl e
or
.Ic set Fl o Ic errexit
option were set.
.Dv EXIT
handlers are executed in the environment of the last executed command.
.Pp
Note that, for non-interactive shells, the trap handler cannot be changed
for signals that were ignored when the shell started.
.Pp
With no arguments, the current state of the traps that have been set since
the shell started is shown as a series of
.Ic trap
commands.
Note that the output of
.Ic trap
cannot be usefully piped to another process (an artifact of the fact that
traps are cleared when subprocesses are created).
.Pp
The original Korn shell's
.Dv DEBUG
trap and the handling of
.Dv ERR
and
.Dv EXIT
traps in functions are not yet implemented.
.Pp
.It Ic true
A command that exits with a zero value.
.Pp
.It Xo
.Ic global
.Oo Op Ic +\-alpnrtUux
.Op Fl L Ns Op Ar n
.Op Fl R Ns Op Ar n
.Op Fl Z Ns Op Ar n
.Op Fl i Ns Op Ar n
.No \*(Ba Fl f Op Fl tux Oc
.Oo Ar name
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
.It Xo
.Ic typeset
.Oo Op Ic +\-alpnrtUux
.Op Fl LRZ Ns Op Ar n
.Op Fl i Ns Op Ar n
.No \*(Ba Fl f Op Fl tux Oc
.Oo Ar name
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
Display or set parameter attributes.
With no
.Ar name
arguments, parameter attributes are displayed; if no options are used, the
current attributes of all parameters are printed as
.Ic typeset
commands; if an option is given (or
.Ql \-
with no option letter), all parameters and their values with the specified
attributes are printed; if options are introduced with
.Ql + ,
parameter values are not printed.
.Pp
If
.Ar name
arguments are given, the attributes of the named parameters are set
.Pq Ic \-
or cleared
.Pq Ic + .
Values for parameters may optionally be specified.
For
.Ar name Ns \&[*] ,
the change affects the entire array, and no value may be specified.
.Pp
If
.Ic typeset
is used inside a function, any parameters specified are localised.
This is not done by the otherwise identical
.Ic global .
.Em Note :
This means that
.Nm No 's Ic global
command is
.Em not
equivalent to other programming languages' as it does not allow a
function called from another function to access a parameter at truly
global scope, but only prevents putting an accessed one into local scope.
.Pp
When
.Fl f
is used,
.Ic typeset
operates on the attributes of functions.
As with parameters, if no
.Ar name
arguments are given,
functions are listed with their values (i.e. definitions) unless
options are introduced with
.Ql + ,
in which case only the function names are reported.
.Bl -tag -width Ds
.It Fl a
Indexed array attribute.
.It Fl f
Function mode.
Display or set functions and their attributes, instead of parameters.
.It Fl i Ns Op Ar n
Integer attribute.
.Ar n
specifies the base to use when displaying the integer (if not specified, the
base given in the first assignment is used).
Parameters with this attribute may
be assigned values containing arithmetic expressions.
.It Fl L Ns Op Ar n
Left justify attribute.
.Ar n
specifies the field width.
If
.Ar n
is not specified, the current width of a parameter (or the width of its first
assigned value) is used.
Leading whitespace (and zeros, if used with the
.Fl Z
option) is stripped.
If necessary, values are either truncated or space padded
to fit the field width.
.It Fl l
Lower case attribute.
All upper case characters in values are converted to lower case.
(In the original Korn shell, this parameter meant
.Dq long integer
when used with the
.Fl i
option.)
.It Fl n
Create a bound variable (name reference): any access to the variable
.Ar name
will access the variable
.Ar value
in the current scope (this is different from
.At
.Nm ksh93 ! )
instead.
Also different from
.At
.Nm ksh93
is that
.Ar value
is lazily evaluated at the time
.Ar name
is accessed.
This can be used by functions to access variables whose names are
passed as parametres, instead of using
.Ic eval .
.It Fl p
Print complete
.Ic typeset
commands that can be used to re-create the attributes and values of
parameters.
.It Fl R Ns Op Ar n
Right justify attribute.
.Ar n
specifies the field width.
If
.Ar n
is not specified, the current width of a parameter (or the width of its first
assigned value) is used.
Trailing whitespace is stripped.
If necessary, values are either stripped of leading characters or space
padded to make them fit the field width.
.It Fl r
Read-only attribute.
Parameters with this attribute may not be assigned to or unset.
Once this attribute is set, it cannot be turned off.
.It Fl t
Tag attribute.
Has no meaning to the shell; provided for application use.
.Pp
For functions,
.Fl t
is the trace attribute.
When functions with the trace attribute are executed, the
.Ic xtrace
.Pq Fl x
shell option is temporarily turned on.
.It Fl U
Unsigned integer attribute.
Integers are printed as unsigned values (combine with the
.Fl i
option).
This option is not in the original Korn shell.
.It Fl u
Upper case attribute.
All lower case characters in values are converted to upper case.
(In the original Korn shell, this parameter meant
.Dq unsigned integer
when used with the
.Fl i
option which meant upper case letters would never be used for bases greater
than 10.
See the
.Fl U
option.)
.Pp
For functions,
.Fl u
is the undefined attribute.
See
.Sx Functions
above for the implications of this.
.It Fl x
Export attribute.
Parameters (or functions) are placed in the environment of
any executed commands.
Exported functions are not yet implemented.
.It Fl Z Ns Op Ar n
Zero fill attribute.
If not combined with
.Fl L ,
this is the same as
.Fl R ,
except zero padding is used instead of space padding.
For integers, the number instead of the base is padded.
.El
.Pp
If any of the
.\" long integer ,
.Fl i ,
.Fl L ,
.Fl l ,
.Fl R ,
.Fl U ,
.Fl u ,
or
.Fl Z
options are changed, all others from this set are cleared,
unless they are also given on the same command line.
.Pp
.It Xo
.Ic ulimit
.Op Fl aBCcdefHilMmnOPpqrSsTtVvw
.Op Ar value
.Xc
Display or set process limits.
If no options are used, the file size limit
.Pq Fl f
is assumed.
.Ar value ,
if specified, may be either an arithmetic expression or the word
.Dq unlimited .
The limits affect the shell and any processes created by the shell after a
limit is imposed.
Note that some systems may not allow limits to be increased
once they are set.
Also note that the types of limits available are system
dependent \*(en some systems have only the
.Fl f
limit.
.Bl -tag -width 5n
.It Fl a
Display all limits; unless
.Fl H
is used, soft limits are displayed.
.It Fl B Ar n
Set the socket buffer size to
.Ar n
kibibytes.
.It Fl C Ar n
Set the number of cached threads to
.Ar n .
.It Fl c Ar n
Impose a size limit of
.Ar n
blocks on the size of core dumps.
.It Fl d Ar n
Impose a size limit of
.Ar n
kibibytes on the size of the data area.
.It Fl e Ar n
Set the maximum niceness to
.Ar n .
.It Fl f Ar n
Impose a size limit of
.Ar n
blocks on files written by the shell and its child processes (files of any
size may be read).
.It Fl H
Set the hard limit only (the default is to set both hard and soft limits).
.It Fl i Ar n
Set the number of pending signals to
.Ar n .
.It Fl l Ar n
Impose a limit of
.Ar n
kibibytes on the amount of locked (wired) physical memory.
.It Fl M Ar n
Set the AIO locked memory to
.Ar n
kibibytes.
.It Fl m Ar n
Impose a limit of
.Ar n
kibibytes on the amount of physical memory used.
.It Fl n Ar n
Impose a limit of
.Ar n
file descriptors that can be open at once.
.It Fl O Ar n
Set the number of AIO operations to
.Ar n .
.It Fl P Ar n
Limit the number of threads per process to
.Ar n .
.It Fl p Ar n
Impose a limit of
.Ar n
processes that can be run by the user at any one time.
.It Fl q Ar n
Limit the size of
.Tn POSIX
message queues to
.Ar n
bytes.
.It Fl r Ar n
Set the maximum real-time priority to
.Ar n .
.It Fl S
Set the soft limit only (the default is to set both hard and soft limits).
.It Fl s Ar n
Impose a size limit of
.Ar n
kibibytes on the size of the stack area.
.It Fl T Ar n
Impose a time limit of
.Ar n
real seconds to be used by each process.
.It Fl t Ar n
Impose a time limit of
.Ar n
CPU seconds spent in user mode to be used by each process.
.It Fl V Ar n
Set the number of vnode monitors on Haiku to
.Ar n .
.It Fl v Ar n
Impose a limit of
.Ar n
kibibytes on the amount of virtual memory (address space) used.
.It Fl w Ar n
Impose a limit of
.Ar n
kibibytes on the amount of swap space used.
.El
.Pp
As far as
.Ic ulimit
is concerned, a block is 512 bytes.
.Pp
.It Xo
.Ic umask
.Op Fl S
.Op Ar mask
.Xc
Display or set the file permission creation mask, or umask (see
.Xr umask 2 ) .
If the
.Fl S
option is used, the mask displayed or set is symbolic; otherwise, it is an
octal number.
.Pp
Symbolic masks are like those used by
.Xr chmod 1 .
When used, they describe what permissions may be made available (as opposed to
octal masks in which a set bit means the corresponding bit is to be cleared).
For example,
.Dq ug=rwx,o=
sets the mask so files will not be readable, writable, or executable by
.Dq others ,
and is equivalent (on most systems) to the octal mask
.Dq 007 .
.Pp
.It Xo
.Ic unalias
.Op Fl adt
.Op Ar name ...
.Xc
The aliases for the given names are removed.
If the
.Fl a
option is used, all aliases are removed.
If the
.Fl t
or
.Fl d
options are used, the indicated operations are carried out on tracked or
directory aliases, respectively.
.Pp
.It Xo
.Ic unset
.Op Fl fv
.Ar parameter ...
.Xc
Unset the named parameters
.Po
.Fl v ,
the default
.Pc
or functions
.Pq Fl f .
With
.Ar parameter Ns \&[*] ,
attributes are kept, only values are unset.
.Pp
The exit status is non-zero if any of the parameters have the read-only
attribute set, zero otherwise.
.Pp
.It Ic wait Op Ar job ...
Wait for the specified job(s) to finish.
The exit status of
.Ic wait
is that of the last specified job; if the last job is killed by a signal, the
exit status is 128 + the number of the signal (see
.Ic kill Fl l Ar exit-status
above); if the last specified job can't be found (because it never existed, or
had already finished), the exit status of
.Ic wait
is 127.
See
.Sx Job control
below for the format of
.Ar job .
.Ic wait
will return if a signal for which a trap has been set is received, or if a
.Dv SIGHUP ,
.Dv SIGINT ,
or
.Dv SIGQUIT
signal is received.
.Pp
If no jobs are specified,
.Ic wait
waits for all currently running jobs (if any) to finish and exits with a zero
status.
If job monitoring is enabled, the completion status of jobs is printed
(this is not the case when jobs are explicitly specified).
.Pp
.It Xo
.Ic whence
.Op Fl pv
.Op Ar name ...
.Xc
For each
.Ar name ,
the type of command is listed (reserved word, built-in, alias,
function, tracked alias, or executable).
If the
.Fl p
option is used, a path search is performed even if
.Ar name
is a reserved word, alias, etc.
Without the
.Fl v
option,
.Ic whence
is similar to
.Ic command Fl v
except that
.Ic whence
will find reserved words and won't print aliases as alias commands.
With the
.Fl v
option,
.Ic whence
is the same as
.Ic command Fl V .
Note that for
.Ic whence ,
the
.Fl p
option does not affect the search path used, as it does for
.Ic command .
If the type of one or more of the names could not be determined, the exit
status is non-zero.
.El
.Ss Job control
Job control refers to the shell's ability to monitor and control jobs which
are processes or groups of processes created for commands or pipelines.
At a minimum, the shell keeps track of the status of the background (i.e.\&
asynchronous) jobs that currently exist; this information can be displayed
using the
.Ic jobs
commands.
If job control is fully enabled (using
.Ic set Fl m
or
.Ic set Fl o Ic monitor ) ,
as it is for interactive shells, the processes of a job are placed in their
own process group.
Foreground jobs can be stopped by typing the suspend
character from the terminal (normally \*(haZ), jobs can be restarted in either the
foreground or background using the
.Ic fg
and
.Ic bg
commands, and the state of the terminal is saved or restored when a foreground
job is stopped or restarted, respectively.
.Pp
Note that only commands that create processes (e.g. asynchronous commands,
subshell commands, and non-built-in, non-function commands) can be stopped;
commands like
.Ic read
cannot be.
.Pp
When a job is created, it is assigned a job number.
For interactive shells, this number is printed inside
.Dq \&[..] ,
followed by the process IDs of the processes in the job when an asynchronous
command is run.
A job may be referred to in the
.Ic bg ,
.Ic fg ,
.Ic jobs ,
.Ic kill ,
and
.Ic wait
commands either by the process ID of the last process in the command pipeline
(as stored in the
.Ic $!\&
parameter) or by prefixing the job number with a percent
sign
.Pq Sq % .
Other percent sequences can also be used to refer to jobs:
.Bl -tag -width "%+ x %% x %XX"
.It %+ \*(Ba %% \*(Ba %
The most recently stopped job, or, if there are no stopped jobs, the oldest
running job.
.It %\-
The job that would be the
.Ic %+
job if the latter did not exist.
.It % Ns Ar n
The job with job number
.Ar n .
.It %? Ns Ar string
The job with its command containing the string
.Ar string
(an error occurs if multiple jobs are matched).
.It % Ns Ar string
The job with its command starting with the string
.Ar string
(an error occurs if multiple jobs are matched).
.El
.Pp
When a job changes state (e.g. a background job finishes or foreground job is
stopped), the shell prints the following status information:
.Pp
.D1 [ Ns Ar number ] Ar flag status command
.Pp
where...
.Bl -tag -width "command"
.It Ar number
is the job number of the job;
.It Ar flag
is the
.Ql +
or
.Ql \-
character if the job is the
.Ic %+
or
.Ic %\-
job, respectively, or space if it is neither;
.It Ar status
indicates the current state of the job and can be:
.Bl -tag -width "RunningXX"
.It Done Op Ar number
The job exited.
.Ar number
is the exit status of the job which is omitted if the status is zero.
.It Running
The job has neither stopped nor exited (note that running does not necessarily
mean consuming CPU time \*(en
the process could be blocked waiting for some event).
.It Stopped Op Ar signal
The job was stopped by the indicated
.Ar signal
(if no signal is given, the job was stopped by
.Dv SIGTSTP ) .
.It Ar signal-description Op Dq core dumped
The job was killed by a signal (e.g. memory fault, hangup); use
.Ic kill Fl l
for a list of signal descriptions.
The
.Dq core dumped
message indicates the process created a core file.
.El
.It Ar command
is the command that created the process.
If there are multiple processes in
the job, each process will have a line showing its
.Ar command
and possibly its
.Ar status ,
if it is different from the status of the previous process.
.El
.Pp
When an attempt is made to exit the shell while there are jobs in the stopped
state, the shell warns the user that there are stopped jobs and does not exit.
If another attempt is immediately made to exit the shell, the stopped jobs are
sent a
.Dv SIGHUP
signal and the shell exits.
Similarly, if the
.Ic nohup
option is not set and there are running jobs when an attempt is made to exit
a login shell, the shell warns the user and does not exit.
If another attempt
is immediately made to exit the shell, the running jobs are sent a
.Dv SIGHUP
signal and the shell exits.
.Ss POSIX mode
Entering
.Ic set Fl o Ic posix
mode will cause
.Nm
to behave even more
.Tn POSIX
compliant in places where the defaults or opinions differ.
Note that
.Nm mksh
will still operate with unsigned 32-bit arithmetics; use
.Nm lksh
if arithmetics on the host
.Vt long
data type, complete with ISO C Undefined Behaviour, are required;
refer to the
.Xr lksh 1
manual page for details.
Most other historic,
.At
.Nm ksh Ns -compatible ,
or opinionated differences can be disabled by using this mode; these are:
.Bl -bullet
.It
The GNU
.Nm bash
I/O redirection
.Ic &\*(Gt Ns Ar file
is no longer supported.
.It
File descriptors created by I/O redirections are inherited by
child processes.
.It
Numbers with a leading digit zero are interpreted as octal.
.It
The
.Nm echo
builtin does not interpret backslashes and only supports the exact option
.Dq Fl n .
.It
\&... (list is incomplete and may change for R53)
.El
.Ss SH mode
Compatibility mode; intended for use with legacy scripts that
cannot easily be fixed; the changes are as follows:
.Bl -bullet
.It
The GNU
.Nm bash
I/O redirection
.Ic &\*(Gt Ns Ar file
is no longer supported.
.It
File descriptors created by I/O redirections are inherited by
child processes.
.It
The
.Nm echo
builtin does not interpret backslashes and only supports the exact option
.Dq Fl n .
.It
\&... (list is incomplete and may change for R53)
.El
.Ss Interactive input line editing
The shell supports three modes of reading command lines from a
.Xr tty 4
in an interactive session, controlled by the
.Ic emacs ,
.Ic gmacs ,
and
.Ic vi
options (at most one of these can be set at once).
The default is
.Ic emacs .
Editing modes can be set explicitly using the
.Ic set
built-in.
If none of these options are enabled,
the shell simply reads lines using the normal
.Xr tty 4
driver.
If the
.Ic emacs
or
.Ic gmacs
option is set, the shell allows emacs-like editing of the command; similarly,
if the
.Ic vi
option is set, the shell allows vi-like editing of the command.
These modes are described in detail in the following sections.
.Pp
In these editing modes, if a line is longer than the screen width (see the
.Ev COLUMNS
parameter),
a
.Ql \*(Gt ,
.Ql + ,
or
.Ql \*(Lt
character is displayed in the last column indicating that there are more
characters after, before and after, or before the current position,
respectively.
The line is scrolled horizontally as necessary.
.Pp
Completed lines are pushed into the history, unless they begin with an
IFS octet or IFS white space, or are the same as the previous line.
.Ss Emacs editing mode
When the
.Ic emacs
option is set, interactive input line editing is enabled.
Warning: This mode is
slightly different from the emacs mode in the original Korn shell.
In this mode, various editing commands
(typically bound to one or more control characters) cause immediate actions
without waiting for a newline.
Several editing commands are bound to particular
control characters when the shell is invoked; these bindings can be changed
using the
.Ic bind
command.
.Pp
The following is a list of available editing commands.
Each description starts with the name of the command,
suffixed with a colon;
an
.Op Ar n
(if the command can be prefixed with a count); and any keys the command is
bound to by default, written using caret notation
e.g. the ASCII ESC character is written as \*(ha[.
These control sequences are not case sensitive.
A count prefix for a command is entered using the sequence
.Pf \*(ha[ Ns Ar n ,
where
.Ar n
is a sequence of 1 or more digits.
Unless otherwise specified, if a count is
omitted, it defaults to 1.
.Pp
Note that editing command names are used only with the
.Ic bind
command.
Furthermore, many editing commands are useful only on terminals with
a visible cursor.
The default bindings were chosen to resemble corresponding
Emacs key bindings.
The user's
.Xr tty 4
characters (e.g.\&
.Dv ERASE )
are bound to
reasonable substitutes and override the default bindings.
.Bl -tag -width Ds
.It abort: \*(haC, \*(haG
Abort the current command, empty the line buffer and
set the exit state to interrupted.
.It auto\-insert: Op Ar n
Simply causes the character to appear as literal input.
Most ordinary characters are bound to this.
.It Xo backward\-char:
.Op Ar n
.No \*(haB , \*(haXD , ANSI-CurLeft , PC-CurLeft
.Xc
Moves the cursor backward
.Ar n
characters.
.It Xo backward\-word:
.Op Ar n
.No \*(ha[b , ANSI-Ctrl-CurLeft , ANSI-Alt-CurLeft
.Xc
Moves the cursor backward to the beginning of the word; words consist of
alphanumerics, underscore
.Pq Sq _ ,
and dollar sign
.Pq Sq $
characters.
.It beginning\-of\-history: \*(ha[\*(Lt
Moves to the beginning of the history.
.It beginning\-of\-line: \*(haA, ANSI-Home, PC-Home
Moves the cursor to the beginning of the edited input line.
.It Xo capitalise\-word:
.Op Ar n
.No \*(ha[C , \*(ha[c
.Xc
Uppercase the first character in the next
.Ar n
words, leaving the cursor past the end of the last word.
.It clear\-screen: \*(ha[\*(haL
Prints a compile-time configurable sequence to clear the screen and home
the cursor, redraws the entire prompt and the currently edited input line.
The default sequence works for almost all standard terminals.
.It comment: \*(ha[#
If the current line does not begin with a comment character, one is added at
the beginning of the line and the line is entered (as if return had been
pressed); otherwise, the existing comment characters are removed and the cursor
is placed at the beginning of the line.
.It complete: \*(ha[\*(ha[
Automatically completes as much as is unique of the command name or the file
name containing the cursor.
If the entire remaining command or file name is
unique, a space is printed after its completion, unless it is a directory name
in which case
.Ql /
is appended.
If there is no command or file name with the current partial word
as its prefix, a bell character is output (usually causing a beep to be
sounded).
.It complete\-command: \*(haX\*(ha[
Automatically completes as much as is unique of the command name having the
partial word up to the cursor as its prefix, as in the
.Ic complete
command above.
.It complete\-file: \*(ha[\*(haX
Automatically completes as much as is unique of the file name having the
partial word up to the cursor as its prefix, as in the
.Ic complete
command described above.
.It complete\-list: \*(haI, \*(ha[=
Complete as much as is possible of the current word,
and list the possible completions for it.
If only one completion is possible,
match as in the
.Ic complete
command above.
Note that \*(haI is usually generated by the TAB (tabulator) key.
.It Xo delete\-char\-backward:
.Op Ar n
.No ERASE , \*(ha? , \*(haH
.Xc
Deletes
.Ar n
characters before the cursor.
.It Xo delete\-char\-forward:
.Op Ar n
.No ANSI-Del , PC-Del
.Xc
Deletes
.Ar n
characters after the cursor.
.It Xo delete\-word\-backward:
.Op Ar n
.No WERASE , \*(ha[\*(ha? , \*(ha[\*(haH , \*(ha[h
.Xc
Deletes
.Ar n
words before the cursor.
.It Xo delete\-word\-forward:
.Op Ar n
.No \*(ha[d
.Xc
Deletes characters after the cursor up to the end of
.Ar n
words.
.It Xo down\-history:
.Op Ar n
.No \*(haN , \*(haXB , ANSI-CurDown , PC-CurDown
.Xc
Scrolls the history buffer forward
.Ar n
lines (later).
Each input line originally starts just after the last entry
in the history buffer, so
.Ic down\-history
is not useful until either
.Ic search\-history ,
.Ic search\-history\-up
or
.Ic up\-history
has been performed.
.It Xo downcase\-word:
.Op Ar n
.No \*(ha[L , \*(ha[l
.Xc
Lowercases the next
.Ar n
words.
.It Xo edit\-line:
.Op Ar n
.No \*(haXe
.Xc
Edit line
.Ar n
or the current line, if not specified, interactively.
The actual command executed is
.Ic fc \-e ${VISUAL:\-${EDITOR:\-vi}} Ar n .
.It end\-of\-history: \*(ha[\*(Gt
Moves to the end of the history.
.It end\-of\-line: \*(haE, ANSI-End, PC-End
Moves the cursor to the end of the input line.
.It eot: \*(ha_
Acts as an end-of-file; this is useful because edit-mode input disables
normal terminal input canonicalization.
.It Xo eot\-or\-delete:
.Op Ar n
.No \*(haD
.Xc
Acts as
.Ic eot
if alone on a line; otherwise acts as
.Ic delete\-char\-forward .
.It error: (not bound)
Error (ring the bell).
.It exchange\-point\-and\-mark: \*(haX\*(haX
Places the cursor where the mark is and sets the mark to where the cursor was.
.It expand\-file: \*(ha[*
Appends a
.Ql *
to the current word and replaces the word with the result of performing file
globbing on the word.
If no files match the pattern, the bell is rung.
.It Xo forward\-char:
.Op Ar n
.No \*(haF , \*(haXC , ANSI-CurRight , PC-CurRight
.Xc
Moves the cursor forward
.Ar n
characters.
.It Xo forward\-word:
.Op Ar n
.No \*(ha[f , ANSI-Ctrl-CurRight , ANSI-Alt-CurRight
.Xc
Moves the cursor forward to the end of the
.Ar n Ns th
word.
.It Xo goto\-history:
.Op Ar n
.No \*(ha[g
.Xc
Goes to history number
.Ar n .
.It kill\-line: KILL
Deletes the entire input line.
.It kill\-region: \*(haW
Deletes the input between the cursor and the mark.
.It Xo kill\-to\-eol:
.Op Ar n
.No \*(haK
.Xc
Deletes the input from the cursor to the end of the line if
.Ar n
is not specified; otherwise deletes characters between the cursor and column
.Ar n .
.It list: \*(ha[?
Prints a sorted, columnated list of command names or file names (if any) that
can complete the partial word containing the cursor.
Directory names have
.Ql /
appended to them.
.It list\-command: \*(haX?
Prints a sorted, columnated list of command names (if any) that can complete
the partial word containing the cursor.
.It list\-file: \*(haX\*(haY
Prints a sorted, columnated list of file names (if any) that can complete the
partial word containing the cursor.
File type indicators are appended as described under
.Ic list
above.
.It newline: \*(haJ , \*(haM
Causes the current input line to be processed by the shell.
The current cursor position may be anywhere on the line.
.It newline\-and\-next: \*(haO
Causes the current input line to be processed by the shell, and the next line
from history becomes the current line.
This is only useful after an
.Ic up\-history ,
.Ic search\-history
or
.Ic search\-history\-up .
.It no\-op: QUIT
This does nothing.
.It prefix\-1: \*(ha[
Introduces a 2-character command sequence.
.It prefix\-2: \*(haX , \*(ha[[ , \*(ha[O
Introduces a 2-character command sequence.
.It Xo prev\-hist\-word:
.Op Ar n
.No \*(ha[. , \*(ha[_
.Xc
The last word, or, if given, the
.Ar n Ns th
word (zero-based) of the previous (on repeated execution, second-last,
third-last, etc.) command is inserted at the cursor.
Use of this editing command trashes the mark.
.It quote: \*(ha\*(ha , \*(haV
The following character is taken literally rather than as an editing command.
.It redraw: \*(haL
Reprints the last line of the prompt string and the current input line
on a new line.
.It Xo search\-character\-backward:
.Op Ar n
.No \*(ha[\*(ha]
.Xc
Search backward in the current line for the
.Ar n Ns th
occurrence of the next character typed.
.It Xo search\-character\-forward:
.Op Ar n
.No \*(ha]
.Xc
Search forward in the current line for the
.Ar n Ns th
occurrence of the next character typed.
.It search\-history: \*(haR
Enter incremental search mode.
The internal history list is searched
backwards for commands matching the input.
An initial
.Ql \*(ha
in the search string anchors the search.
The escape key will leave search mode.
Other commands, including sequences of escape as
.Ic prefix\-1
followed by a
.Ic prefix\-1
or
.Ic prefix\-2
key will be executed after leaving search mode.
The
.Ic abort Pq \*(haG
command will restore the input line before search started.
Successive
.Ic search\-history
commands continue searching backward to the next previous occurrence of the
pattern.
The history buffer retains only a finite number of lines; the oldest
are discarded as necessary.
.It search\-history\-up: ANSI-PgUp, PC-PgUp
Search backwards through the history buffer for commands whose beginning match
the portion of the input line before the cursor.
When used on an empty line, this has the same effect as
.Ic up\-history .
.It search\-history\-down: ANSI-PgDn, PC-PgDn
Search forwards through the history buffer for commands whose beginning match
the portion of the input line before the cursor.
When used on an empty line, this has the same effect as
.Ic down\-history .
This is only useful after an
.Ic up\-history ,
.Ic search\-history
or
.Ic search\-history\-up .
.It set\-mark\-command: \*(ha[ Ns Aq space
Set the mark at the cursor position.
.It transpose\-chars: \*(haT
If at the end of line, or if the
.Ic gmacs
option is set, this exchanges the two previous characters; otherwise, it
exchanges the previous and current characters and moves the cursor one
character to the right.
.It Xo up\-history:
.Op Ar n
.No \*(haP , \*(haXA , ANSI-CurUp , PC-CurUp
.Xc
Scrolls the history buffer backward
.Ar n
lines (earlier).
.It Xo upcase\-word:
.Op Ar n
.No \*(ha[U , \*(ha[u
.Xc
Uppercase the next
.Ar n
words.
.It version: \*(ha[\*(haV
Display the version of
.Nm mksh .
The current edit buffer is restored as soon as a key is pressed.
The restoring keypress is processed, unless it is a space.
.It yank: \*(haY
Inserts the most recently killed text string at the current cursor position.
.It yank\-pop: \*(ha[y
Immediately after a
.Ic yank ,
replaces the inserted text string with the next previously killed text string.
.El
.Ss Vi editing mode
.Em Note:
The vi command-line editing mode is orphaned, yet still functional.
It is 8-bit clean but specifically does not support UTF-8 or MBCS.
.Pp
The vi command-line editor in
.Nm
has basically the same commands as the
.Xr vi 1
editor with the following exceptions:
.Bl -bullet
.It
You start out in insert mode.
.It
There are file name and command completion commands:
=, \e, *, \*(haX, \*(haE, \*(haF, and, optionally,
.Aq tab
and
.Aq esc .
.It
The
.Ic _
command is different (in
.Nm mksh ,
it is the last argument command; in
.Xr vi 1
it goes to the start of the current line).
.It
The
.Ic /
and
.Ic G
commands move in the opposite direction to the
.Ic j
command.
.It
Commands which don't make sense in a single line editor are not available
(e.g. screen movement commands and
.Xr ex 1 Ns -style
colon
.Pq Ic \&:
commands).
.El
.Pp
Like
.Xr vi 1 ,
there are two modes:
.Dq insert
mode and
.Dq command
mode.
In insert mode, most characters are simply put in the buffer at the
current cursor position as they are typed; however, some characters are
treated specially.
In particular, the following characters are taken from current
.Xr tty 4
settings
(see
.Xr stty 1 )
and have their usual meaning (normal values are in parentheses): kill (\*(haU),
erase (\*(ha?), werase (\*(haW), eof (\*(haD), intr (\*(haC), and quit (\*(ha\e).
In addition to
the above, the following characters are also treated specially in insert mode:
.Bl -tag -width XJXXXXM
.It \*(haE
Command and file name enumeration (see below).
.It \*(haF
Command and file name completion (see below).
If used twice in a row, the
list of possible completions is displayed; if used a third time, the completion
is undone.
.It \*(haH
Erases previous character.
.It \*(haJ \*(Ba \*(haM
End of line.
The current line is read, parsed, and executed by the shell.
.It \*(haV
Literal next.
The next character typed is not treated specially (can be used
to insert the characters being described here).
.It \*(haX
Command and file name expansion (see below).
.It Aq esc
Puts the editor in command mode (see below).
.It Aq tab
Optional file name and command completion (see
.Ic \*(haF
above), enabled with
.Ic set Fl o Ic vi\-tabcomplete .
.El
.Pp
In command mode, each character is interpreted as a command.
Characters that
don't correspond to commands, are illegal combinations of commands, or are
commands that can't be carried out, all cause beeps.
In the following command descriptions, an
.Op Ar n
indicates the command may be prefixed by a number (e.g.\&
.Ic 10l
moves right 10 characters); if no number prefix is used,
.Ar n
is assumed to be 1 unless otherwise specified.
The term
.Dq current position
refers to the position between the cursor and the character preceding the
cursor.
A
.Dq word
is a sequence of letters, digits, and underscore characters or a sequence of
non-letter, non-digit, non-underscore, and non-whitespace characters (e.g.\&
.Dq ab2*&\*(ha
contains two words) and a
.Dq big-word
is a sequence of non-whitespace characters.
.Pp
Special
.Nm
vi commands:
.Pp
The following commands are not in, or are different from, the normal vi file
editor:
.Bl -tag -width 10n
.It Xo
.Oo Ar n Oc Ns _
.Xc
Insert a space followed by the
.Ar n Ns th
big-word from the last command in the history at the current position and enter
insert mode; if
.Ar n
is not specified, the last word is inserted.
.It #
Insert the comment character
.Pq Sq #
at the start of the current line and return the line to the shell (equivalent
to
.Ic I#\*(haJ ) .
.It Xo
.Oo Ar n Oc Ns g
.Xc
Like
.Ic G ,
except if
.Ar n
is not specified, it goes to the most recent remembered line.
.It Xo
.Oo Ar n Oc Ns v
.Xc
Edit line
.Ar n
using the
.Xr vi 1
editor; if
.Ar n
is not specified, the current line is edited.
The actual command executed is
.Ic fc \-e ${VISUAL:\-${EDITOR:\-vi}} Ar n .
.It * and \*(haX
Command or file name expansion is applied to the current big-word (with an
appended
.Ql *
if the word contains no file globbing characters) \*(en the big-word is replaced
with the resulting words.
If the current big-word is the first on the line
or follows one of the characters
.Ql \&; ,
.Ql \*(Ba ,
.Ql & ,
.Ql \&( ,
or
.Ql \&) ,
and does not contain a slash
.Pq Sq / ,
then command expansion is done; otherwise file name expansion is done.
Command expansion will match the big-word against all aliases, functions, and
built-in commands as well as any executable files found by searching the
directories in the
.Ev PATH
parameter.
File name expansion matches the big-word against the files in the
current directory.
After expansion, the cursor is placed just past the last
word and the editor is in insert mode.
.It Xo
.Oo Ar n Oc Ns \e ,
.Oo Ar n Oc Ns \*(haF ,
.Oo Ar n Oc Ns Aq tab ,
.No and
.Oo Ar n Oc Ns Aq esc
.Xc
Command/file name completion.
Replace the current big-word with the
longest unique match obtained after performing command and file name expansion.
.Aq tab
is only recognised if the
.Ic vi\-tabcomplete
option is set, while
.Aq esc
is only recognised if the
.Ic vi\-esccomplete
option is set (see
.Ic set Fl o ) .
If
.Ar n
is specified, the
.Ar n Ns th
possible completion is selected (as reported by the command/file name
enumeration command).
.It = and \*(haE
Command/file name enumeration.
List all the commands or files that match the current big-word.
.It \*(haV
Display the version of
.Nm mksh .
The current edit buffer is restored as soon as a key is pressed.
The restoring keypress is ignored.
.It @ Ns Ar c
Macro expansion.
Execute the commands found in the alias
.Ar c .
.El
.Pp
Intra-line movement commands:
.Bl -tag -width Ds
.It Xo
.Oo Ar n Oc Ns h and
.Oo Ar n Oc Ns \*(haH
.Xc
Move left
.Ar n
characters.
.It Xo
.Oo Ar n Oc Ns l and
.Oo Ar n Oc Ns Aq space
.Xc
Move right
.Ar n
characters.
.It 0
Move to column 0.
.It \*(ha
Move to the first non-whitespace character.
.It Xo
.Oo Ar n Oc Ns \*(Ba
.Xc
Move to column
.Ar n .
.It $
Move to the last character.
.It Xo
.Oo Ar n Oc Ns b
.Xc
Move back
.Ar n
words.
.It Xo
.Oo Ar n Oc Ns B
.Xc
Move back
.Ar n
big-words.
.It Xo
.Oo Ar n Oc Ns e
.Xc
Move forward to the end of the word,
.Ar n
times.
.It Xo
.Oo Ar n Oc Ns E
.Xc
Move forward to the end of the big-word,
.Ar n
times.
.It Xo
.Oo Ar n Oc Ns w
.Xc
Move forward
.Ar n
words.
.It Xo
.Oo Ar n Oc Ns W
.Xc
Move forward
.Ar n
big-words.
.It %
Find match.
The editor looks forward for the nearest parenthesis, bracket, or
brace and then moves the cursor to the matching parenthesis, bracket, or brace.
.It Xo
.Oo Ar n Oc Ns f Ns Ar c
.Xc
Move forward to the
.Ar n Ns th
occurrence of the character
.Ar c .
.It Xo
.Oo Ar n Oc Ns F Ns Ar c
.Xc
Move backward to the
.Ar n Ns th
occurrence of the character
.Ar c .
.It Xo
.Oo Ar n Oc Ns t Ns Ar c
.Xc
Move forward to just before the
.Ar n Ns th
occurrence of the character
.Ar c .
.It Xo
.Oo Ar n Oc Ns T Ns Ar c
.Xc
Move backward to just before the
.Ar n Ns th
occurrence of the character
.Ar c .
.It Xo
.Oo Ar n Oc Ns \&;
.Xc
Repeats the last
.Ic f , F , t ,
or
.Ic T
command.
.It Xo
.Oo Ar n Oc Ns \&,
.Xc
Repeats the last
.Ic f , F , t ,
or
.Ic T
command, but moves in the opposite direction.
.El
.Pp
Inter-line movement commands:
.Bl -tag -width Ds
.It Xo
.Oo Ar n Oc Ns j ,
.Oo Ar n Oc Ns + ,
.No and
.Oo Ar n Oc Ns \*(haN
.Xc
Move to the
.Ar n Ns th
next line in the history.
.It Xo
.Oo Ar n Oc Ns k ,
.Oo Ar n Oc Ns \- ,
.No and
.Oo Ar n Oc Ns \*(haP
.Xc
Move to the
.Ar n Ns th
previous line in the history.
.It Xo
.Oo Ar n Oc Ns G
.Xc
Move to line
.Ar n
in the history; if
.Ar n
is not specified, the number of the first remembered line is used.
.It Xo
.Oo Ar n Oc Ns g
.Xc
Like
.Ic G ,
except if
.Ar n
is not specified, it goes to the most recent remembered line.
.It Xo
.Oo Ar n Oc Ns / Ns Ar string
.Xc
Search backward through the history for the
.Ar n Ns th
line containing
.Ar string ;
if
.Ar string
starts with
.Ql \*(ha ,
the remainder of the string must appear at the start of the history line for
it to match.
.It Xo
.Oo Ar n Oc Ns \&? Ns Ar string
.Xc
Same as
.Ic / ,
except it searches forward through the history.
.It Xo
.Oo Ar n Oc Ns n
.Xc
Search for the
.Ar n Ns th
occurrence of the last search string;
the direction of the search is the same as the last search.
.It Xo
.Oo Ar n Oc Ns N
.Xc
Search for the
.Ar n Ns th
occurrence of the last search string;
the direction of the search is the opposite of the last search.
.It Ar ANSI-CurUp , PC-PgUp
Take the characters from the beginning of the line to the current
cursor position as search string and do a backwards history search
for lines beginning with this string; keep the cursor position.
This works only in insert mode and keeps it enabled.
.El
.Pp
Edit commands
.Bl -tag -width Ds
.It Xo
.Oo Ar n Oc Ns a
.Xc
Append text
.Ar n
times; goes into insert mode just after the current position.
The append is
only replicated if command mode is re-entered i.e.\&
.Aq esc
is used.
.It Xo
.Oo Ar n Oc Ns A
.Xc
Same as
.Ic a ,
except it appends at the end of the line.
.It Xo
.Oo Ar n Oc Ns i
.Xc
Insert text
.Ar n
times; goes into insert mode at the current position.
The insertion is only
replicated if command mode is re-entered i.e.\&
.Aq esc
is used.
.It Xo
.Oo Ar n Oc Ns I
.Xc
Same as
.Ic i ,
except the insertion is done just before the first non-blank character.
.It Xo
.Oo Ar n Oc Ns s
.Xc
Substitute the next
.Ar n
characters (i.e. delete the characters and go into insert mode).
.It S
Substitute whole line.
All characters from the first non-blank character to the
end of the line are deleted and insert mode is entered.
.It Xo
.Oo Ar n Oc Ns c Ns Ar move-cmd
.Xc
Change from the current position to the position resulting from
.Ar n move-cmd Ns s
(i.e. delete the indicated region and go into insert mode); if
.Ar move-cmd
is
.Ic c ,
the line starting from the first non-blank character is changed.
.It C
Change from the current position to the end of the line (i.e. delete to the
end of the line and go into insert mode).
.It Xo
.Oo Ar n Oc Ns x
.Xc
Delete the next
.Ar n
characters.
.It Xo
.Oo Ar n Oc Ns X
.Xc
Delete the previous
.Ar n
characters.
.It D
Delete to the end of the line.
.It Xo
.Oo Ar n Oc Ns d Ns Ar move-cmd
.Xc
Delete from the current position to the position resulting from
.Ar n move-cmd Ns s ;
.Ar move-cmd
is a movement command (see above) or
.Ic d ,
in which case the current line is deleted.
.It Xo
.Oo Ar n Oc Ns r Ns Ar c
.Xc
Replace the next
.Ar n
characters with the character
.Ar c .
.It Xo
.Oo Ar n Oc Ns R
.Xc
Replace.
Enter insert mode but overwrite existing characters instead of
inserting before existing characters.
The replacement is repeated
.Ar n
times.
.It Xo
.Oo Ar n Oc Ns \*(TI
.Xc
Change the case of the next
.Ar n
characters.
.It Xo
.Oo Ar n Oc Ns y Ns Ar move-cmd
.Xc
Yank from the current position to the position resulting from
.Ar n move-cmd Ns s
into the yank buffer; if
.Ar move-cmd
is
.Ic y ,
the whole line is yanked.
.It Y
Yank from the current position to the end of the line.
.It Xo
.Oo Ar n Oc Ns p
.Xc
Paste the contents of the yank buffer just after the current position,
.Ar n
times.
.It Xo
.Oo Ar n Oc Ns P
.Xc
Same as
.Ic p ,
except the buffer is pasted at the current position.
.El
.Pp
Miscellaneous vi commands
.Bl -tag -width Ds
.It \*(haJ and \*(haM
The current line is read, parsed, and executed by the shell.
.It \*(haL and \*(haR
Redraw the current line.
.It Xo
.Oo Ar n Oc Ns \&.
.Xc
Redo the last edit command
.Ar n
times.
.It u
Undo the last edit command.
.It U
Undo all changes that have been made to the current line.
.It PC Home, End, Del, and cursor keys
They move as expected, both in insert and command mode.
.It Ar intr No and Ar quit
The interrupt and quit terminal characters cause the current line to be
deleted and a new prompt to be printed.
.El
.Sh FILES
.Bl -tag -width XetcXsuid_profile -compact
.It Pa \*(TI/.mkshrc
User mkshrc profile (non-privileged interactive shells); see
.Sx Startup files.
The location can be changed at compile time (for embedded systems);
AOSP Android builds use
.Pa /system/etc/mkshrc .
.It Pa \*(TI/.profile
User profile (non-privileged login shells); see
.Sx Startup files
near the top of this manual.
.It Pa /etc/profile
System profile (login shells); see
.Sx Startup files.
.It Pa /etc/shells
Shell database.
.It Pa /etc/suid_profile
Suid profile (privileged shells); see
.Sx Startup files.
.El
.Pp
Note: On Android,
.Pa /system/etc/
contains the system and suid profile.
.Sh SEE ALSO
.Xr awk 1 ,
.Xr cat 1 ,
.Xr ed 1 ,
.Xr getopt 1 ,
.Xr lksh 1 ,
.Xr sed 1 ,
.Xr sh 1 ,
.Xr stty 1 ,
.Xr dup 2 ,
.Xr execve 2 ,
.Xr getgid 2 ,
.Xr getuid 2 ,
.Xr mknod 2 ,
.Xr mkfifo 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr rename 2 ,
.Xr wait 2 ,
.Xr getopt 3 ,
.Xr nl_langinfo 3 ,
.Xr setlocale 3 ,
.Xr signal 3 ,
.Xr system 3 ,
.Xr tty 4 ,
.Xr shells 5 ,
.Xr environ 7 ,
.Xr script 7 ,
.Xr utf\-8 7 ,
.Xr mknod 8
.Pp
.Pa https://www.mirbsd.org/ksh\-chan.htm
.Rs
.%A Morris Bolsky
.%B "The KornShell Command and Programming Language"
.%D 1989
.%I "Prentice Hall PTR"
.%P "xvi\ +\ 356 pages"
.%O "ISBN 978\-0\-13\-516972\-8 (0\-13\-516972\-0)"
.Re
.Rs
.%A Morris I. Bolsky
.%A David G. Korn
.%B "The New KornShell Command and Programming Language (2nd Edition)"
.%D 1995
.%I "Prentice Hall PTR"
.%P "xvi\ +\ 400 pages"
.%O "ISBN 978\-0\-13\-182700\-4 (0\-13\-182700\-6)"
.Re
.Rs
.%A Stephen G. Kochan
.%A Patrick H. Wood
.%B "\\*(tNUNIX\\*(sP Shell Programming"
.%V "3rd Edition"
.%D 2003
.%I "Sams"
.%P "xiii\ +\ 437 pages"
.%O "ISBN 978\-0\-672\-32490\-1 (0\-672\-32490\-3)"
.Re
.Rs
.%A "IEEE Inc."
.%T "\\*(tNIEEE\\*(sP Standard for Information Technology \*(en Portable Operating System Interface (POSIX)"
.%V "Part 2: Shell and Utilities"
.%D 1993
.%I "IEEE Press"
.%P "xvii\ +\ 1195 pages"
.%O "ISBN 978\-1\-55937\-255\-8 (1\-55937\-255\-9)"
.Re
.Rs
.%A Bill Rosenblatt
.%B "Learning the Korn Shell"
.%D 1993
.%I "O'Reilly"
.%P "360 pages"
.%O "ISBN 978\-1\-56592\-054\-5 (1\-56592\-054\-6)"
.Re
.Rs
.%A Bill Rosenblatt
.%A Arnold Robbins
.%B "Learning the Korn Shell, Second Edition"
.%D 2002
.%I "O'Reilly"
.%P "432 pages"
.%O "ISBN 978\-0\-596\-00195\-7 (0\-596\-00195\-9)"
.Re
.Rs
.%A Barry Rosenberg
.%B "KornShell Programming Tutorial"
.%D 1991
.%I "Addison-Wesley Professional"
.%P "xxi\ +\ 324 pages"
.%O "ISBN 978\-0\-201\-56324\-5 (0\-201\-56324\-X)"
.Re
.Sh AUTHORS
.An -nosplit
.Nm "The MirBSD Korn Shell"
is developed by
.An mirabilos Aq Mt m@mirbsd.org
as part of The MirOS Project.
This shell is based on the public domain 7th edition Bourne shell clone by
.An Charles Forsyth ,
who kindly agreed to, in countries where the Public Domain status of the work
may not be valid, grant a copyright licence to the general public to deal in
the work without restriction and permission to sublicence derivates under the
terms of any (OSI approved) Open Source licence,
and parts of the BRL shell by
.An Doug A. Gwyn ,
.An Doug Kingston ,
.An Ron Natalie ,
.An Arnold Robbins ,
.An Lou Salkind ,
and others.
The first release of
.Nm pdksh
was created by
.An Eric Gisin ,
and it was subsequently maintained by
.An John R. MacMillan ,
.An Simon J. Gerraty ,
and
.An Michael Rendell .
The effort of several projects, such as Debian and OpenBSD, and other
contributors including our users, to improve the shell is appreciated.
See the documentation, CVS, and web site for details.
.Pp
The BSD daemon is Copyright \(co Marshall Kirk McKusick.
The complete legalese is at:
.Pa https://www.mirbsd.org/TaC\-mksh.txt
.\"
.\" This boils down to: feel free to use mksh.ico as application icon
.\" or shortcut for mksh or mksh/Win32 or OS/2; distro patches are ok
.\" (but we request they amend $KSH_VERSION when modifying mksh).
.\" Authors are Marshall Kirk McKusick (UCB), Rick Collette (ekkoBSD),
.\" mirabilos, Benny Siegert (MirBSD), Michael Langguth (mksh/Win32),
.\" KO Myung-Hun (mksh for OS/2).
.\"
.\" As far as MirBSD is concerned, the files themselves are free
.\" to modification and distribution under BSD/MirOS Licence, the
.\" restriction on use stems only from trademark law's requirement
.\" to protect it or lose it, which McKusick almost did.
.\"
.Sh CAVEATS
.Nm
has a different scope model from
.At
.Nm ksh ,
which leads to subtile differences in semantics for identical builtins.
This can cause issues with a
.Ic nameref
to suddenly point to a local variable by accident; fixing this is hard.
.Pp
The parts of a pipeline, like below, are executed in subshells.
Thus, variable assignments inside them are not visible in the
surrounding execution environment.
Use co-processes instead.
.Bd -literal -offset indent
foo \*(Ba bar \*(Ba read baz            # will not change $baz
foo \*(Ba bar \*(Ba& read \-p baz        # will, however, do so
.Ed
.Pp
.Nm mksh
provides a consistent set of 32-bit integer arithmetics, both signed
and unsigned, with defined wraparound and sign of the result of a
remainder operation, even (defying POSIX) on 36-bit and 64-bit systems.
.Pp
.Nm mksh
provides a consistent, clear interface normally.
This may deviate from POSIX in historic or opinionated places.
.Ic set Fl o Ic posix
(see
.Sx POSIX mode
for details)
will cause the shell to behave more conformant.
.Pp
For the purpose of
.Tn POSIX ,
.Nm mksh
supports only the
.Dq C
locale.
.Nm mksh Ns 's
.Ic utf8\-mode
only supports the Unicode BMP (Basic Multilingual Plane) and maps
raw octets into the U+EF80..U+EFFF wide character range; compare
.Sx Arithmetic expressions .
The following
.Tn POSIX
.Nm sh
code toggles the
.Ic utf8\-mode
option dependent on the current
.Tn POSIX
locale for mksh to allow using the UTF-8 mode, within the constraints
outlined above, in code portable across various shell implementations:
.Bd -literal -offset indent
case ${KSH_VERSION:\-} in
*MIRBSD\ KSH*\*(Ba*LEGACY\ KSH*)
	case ${LC_ALL:\-${LC_CTYPE:\-${LANG:\-}}} in
	*[Uu][Tt][Ff]8*\*(Ba*[Uu][Tt][Ff]\-8*) set \-U ;;
	*) set +U ;;
	esac ;;
esac
.Ed
In near future, (Unicode) locale tracking will be implemented though.
.Sh BUGS
Suspending (using \*(haZ) pipelines like the one below will only suspend
the currently running part of the pipeline; in this example,
.Dq fubar
is immediately printed on suspension (but not later after an
.Ic fg ) .
.Bd -literal -offset indent
$ /bin/sleep 666 && echo fubar
.Ed
.Pp
The truncation process involved when changing
.Ev HISTFILE
does not free old history entries (leaks memory) and leaks
old entries into the new history if their line numbers are
not overwritten by same-numer entries from the persistent
history file; truncating the on-disc file to
.Ev HISTSIZE
lines has always been broken and prone to history file corruption
when multiple shells are accessing the file; the rollover process
for the in-memory portion of the history is slow, should use
.Xr memmove 3 .
.Pp
Handling of backslash plus double-quote inside the (deprecated)
.Pf \` Ns Ar command Ns \`
form of command substitution when the substitution itself is
also inside double quotes currently deliberately violates
.Tn POSIX
even in
.Fl o Ic posix
mode until Austin group bug 1015 has been resolved either way,
as the current wording of the standard prohibits the current
and historic practice of several shells which several scripts
(admittedly wrongly) depend on.
.Pp
This document attempts to describe
.Nm mksh\ R52b
and up,
.\" with vendor patches from insert-your-name-here,
compiled without any options impacting functionality, such as
.Dv MKSH_SMALL ,
when not called as
.Pa /bin/sh
which, on some systems only, enables
.Ic set Fl o Ic posix
or
.Ic set Fl o Ic sh
automatically (whose behaviour differs across targets),
for an operating environment supporting all of its advanced needs.
.Pp
Please report bugs in
.Nm
to the
.Mx
mailing list at
.Aq Mt miros\-mksh@mirbsd.org
or in the
.Li \&#\&!/bin/mksh
.Pq or Li \&#ksh
IRC channel at
.Pa irc.freenode.net
.Pq Port 6697 SSL, 6667 unencrypted ,
or at:
.Pa https://launchpad.net/mksh