mksh/lksh.1

.\" $MirOS: src/bin/mksh/lksh.1,v 1.17 2016/02/11 20:12:09 tg Exp $
.\"-
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.\" damage or existence of a defect, except proven that it results out
.\" of said person’s immediate fault when using the work as intended.
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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.
.Pp
Note that it's strongly recommended to invoke
.Nm
with at least the
.Fl o Ic posix
option, if not both that
.Em and Fl o Ic sh ,
to fully enjoy better compatibility to the
.Tn POSIX
standard (which is probably why you use
.Nm
over
.Nm mksh
in the first place) or legacy scripts, respectively.
.Sh LEGACY MODE
.Nm
currently has the following differences from
.Nm mksh :
.Bl -bullet
.It
.\"XXX TODO: remove (some systems may wish to have lksh as ksh)
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
uses
.Tn POSIX
arithmetics, which has quite a few implications:
The data type for arithmetics is the host
.Tn ISO
C
.Vt long
data type.
Signed integer wraparound is Undefined Behaviour; this means that...
.Bd -literal -offset indent
$ echo $((2147483647 + 1))
.Ed
.Pp
\&... is permitted to, e.g. delete all files on your system
(the figure differs for non-32-bit systems, the rule doesn't).
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 (see above for an example).
.It
.Nm
only offers the traditional ten file descriptors to scripts.
.It
.\"XXX TODO: move this to FPOSIX
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
.\"XXX TODO: move this to FPOSIX
The
.Tn GNU
.Nm bash
extension &\*(Gt to redirect stdout and stderr in one go is not parsed.
.It
.\"XXX TODO: drop along with allowing interactivity
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
.\"XXX TODO: move to FPOSIX/FSH
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
Functions defined with the
.Ic function
reserved word share the shell options
.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
The distinction between the shell variants
.Pq Nm lksh / Nm mksh
and shell flags
.Pq Fl o Ic posix / Ic sh
will be reworked for an upcoming release.
.Pp
To use
.Nm
as
.Pa /bin/sh ,
compilation to enable
.Ic set -o posix
by default if called as
.Nm sh
is highly recommended for better standards compliance.
For better compatibility with legacy scripts, such as many
.Tn Debian
maintainer scripts, Upstart and SYSV init scripts, and other
unfixed scripts, using the compile-time options for enabling
.Em both
.Ic set -o posix -o sh
when the shell is run as
.Nm sh
is recommended.
.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 currently 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 .