mksh/lksh.1

.\" $MirOS: src/bin/mksh/lksh.1,v 1.9 2015/04/11 23:28:19 tg Exp $
.\"-
.\" Copyright (c) 2008, 2009, 2010, 2012, 2013, 2015
.\"	Thorsten “mirabilos” Glaser <tg@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‐
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.\" merge, give away, or sublicence.
.\"
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.\" 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.
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.\" additional code to convene between the UCB mdoc macropackage (and
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.el \{\
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.ie "\*(tT"gnu" \{\
.	eo
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.	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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.	if (\n[arg-limit] > \n[arg-ptr]) \{\
.	nr arg-ptr +1
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.	as str-Mx1 \~\*[arg\n[arg-ptr]]
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.	print-recursive
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.\"-
.Dt LKSH 1
.Os MirBSD
.Sh NAME
.Nm lksh
.Nd Legacy Korn shell built on mksh
.Sh SYNOPSIS
.Nm
.Bk -words
.Op Fl +abCefhiklmnprUuvXx
.Op Fl +o Ar opt
.Oo
.Fl c Ar string \*(Ba
.Fl s \*(Ba
.Ar file
.Op Ar args ...
.Oc
.Ek
.Sh DESCRIPTION
.Nm
is a command interpreter intended exclusively for running legacy
shell scripts.
It is built on
.Nm mksh ;
refer to its manual page for details on the scripting language.
It is recommended to port scripts to
.Nm mksh
instead of relying on legacy or idiotic POSIX-mandated behaviour,
since the MirBSD Korn Shell scripting language is much more consistent.
.Sh LEGACY MODE
.Nm
currently has the following differences from
.Nm mksh :
.Bl -bullet
.It
There is no explicit support for interactive use,
nor any command line editing or history code.
Hence,
.Nm
is not suitable as a user's login shell, either; use
.Nm mksh
instead.
.It
The
.Ev KSH_VERSION
string identifies
.Nm
as
.Dq LEGACY KSH
instead of
.Dq MIRBSD KSH .
Note that the rest of the version string is identical between
the two shell flavours, and the behaviour and differences can
change between versions; see the accompanying manual page
.Xr mksh 1
for the versions this document applies to.
.It
.Nm
only offers the traditional ten file descriptors to scripts.
.It
.Nm
uses
.Tn POSIX
arithmetics, which has quite a few implications:
The data type for arithmetics is the host ISO C
.Vt long
data type.
Signed integer wraparound is Undefined Behaviour.
The sign of the result of a modulo operation with at least one
negative operand is unspecified.
Shift operations on negative numbers are unspecified.
Division of the largest negative number by \-1 is Undefined Behaviour.
The compiler is permitted to delete all data and crash the system
if Undefined Behaviour occurs.
.It
The rotation arithmetic operators are not available.
.It
The shift arithmetic operators take all bits of the second operand into
account; if they exceed permitted precision, the result is unspecified.
.It
The
.Tn GNU
.Nm bash
extension &\*(Gt to redirect stdout and stderr in one go is not parsed.
.It
The
.Nm mksh
command line option
.Fl T
is not available.
.It
Unless
.Ic set -o posix
is active,
.Nm
always uses traditional mode for constructs like:
.Bd -literal -offset indent
$ set -- $(getopt ab:c "$@")
$ echo $?
.Ed
.Pp
POSIX mandates this to show 0, but traditional mode
passes through the errorlevel from the
.Xr getopt 1
command.
.It
Unlike
.At
.Nm ksh ,
.Nm mksh
in
.Fl o Ic posix
or
.Fl o Ic sh
mode and
.Nm lksh
do not keep file descriptors \*(Gt 2 private from sub-processes.
.It
.Nm lksh
undefines an alias when a
.Tn POSIX
function with the same name is defined,
to make that function immediately callable.
In
.Nm mksh ,
aliases have precedence; the name must be quoted or
.Ic unalias Ns ed
to access it.
.It
Functions defined with the
.Ic function
reserved word share the shell flags
.Pq Ic set -o
instead of locally scoping them.
.El
.Sh SEE ALSO
.Xr mksh 1
.Pp
.Pa https://www.mirbsd.org/mksh.htm
.Pp
.Pa https://www.mirbsd.org/ksh\-chan.htm
.Sh CAVEATS
To use
.Nm
as
.Pa /bin/sh ,
compilation to enable
.Ic set -o posix
by default is highly recommended for better standards compliance.
.Pp
.Nm
tries to make a cross between a legacy bourne/posix compatibl-ish
shell and a legacy pdksh-alike but
.Dq legacy
is not exactly specified.
.Pp
The
.Ic set
built-in command does not have all options one would expect
from a full-blown
.Nm mksh
or
.Nm pdksh .
.Pp
Talk to the
.Mx
development team using the mailing list at
.Aq miros\-mksh@mirbsd.org
or the
.Li \&#\&!/bin/mksh
.Pq or Li \&#ksh
IRC channel at
.Pa irc.freenode.net
.Pq Port 6697 SSL, 6667 unencrypted
if you need any further quirks or assistance,
and consider migrating your legacy scripts to work with
.Nm mksh
instead of requiring
.Nm .