xenial (1) lksh.1.gz

NAME

     lksh — Legacy Korn shell built on mksh

SYNOPSIS

     lksh [-+abCefhiklmnprUuvXx] [-+o opt] [-c string | -s | file [args ...]]

DESCRIPTION

     lksh is a command interpreter intended exclusively for running legacy shell scripts.  It is built on mksh;
     refer to its manual page for details on the scripting language.  It is recommended to port scripts to mksh
     instead of relying on legacy or idiotic POSIX-mandated behaviour, since the MirBSD Korn Shell scripting
     language is much more consistent.

     Note that it's strongly recommended to invoke lksh with at least the -o posix option, if not both that and
     -o sh, to fully enjoy better compatibility to the POSIX standard (which is probably why you use lksh over
     mksh in the first place) or legacy scripts, respectively.

LEGACY MODE

     lksh currently has the following differences from mksh:

     •   There is no explicit support for interactive use, nor any command line editing or history code.  Hence,
         lksh is not suitable as a user's login shell, either; use mksh instead.

     •   The KSH_VERSION string identifies lksh as “LEGACY KSH” instead of “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 mksh(1) for the versions this document
         applies to.

     •   lksh uses POSIX arithmetics, which has quite a few implications: The data type for arithmetics is the
         host ISO C long data type.  Signed integer wraparound is Undefined Behaviour; this means that...

               $ echo $((2147483647 + 1))

         ... 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).

     •   lksh only offers the traditional ten file descriptors to scripts.

     •   The rotation arithmetic operators are not available.

     •   The shift arithmetic operators take all bits of the second operand into account; if they exceed
         permitted precision, the result is unspecified.

     •   The GNU bash extension &> to redirect stdout and stderr in one go is not parsed.

     •   The mksh command line option -T is not available.

     •   Unless set -o posix is active, lksh always uses traditional mode for constructs like:

               $ set -- $(getopt ab:c "$@")
               $ echo $?

         POSIX mandates this to show 0, but traditional mode passes through the errorlevel from the getopt(1)
         command.

     •   Unlike AT&T UNIX ksh, mksh in -o posix or -o sh mode and lksh do not keep file descriptors > 2 private
         from sub-processes.

     •   Functions defined with the function reserved word share the shell options (set -o) instead of locally
         scoping them.

SEE ALSO

     mksh(1)

     https://www.mirbsd.org/mksh.htm

     https://www.mirbsd.org/ksh-chan.htm

CAVEATS

     The distinction between the shell variants (lksh / mksh) and shell flags (-o posix / sh) will be reworked
     for an upcoming release.

     To use lksh as /bin/sh, compilation to enable set -o posix by default if called as sh is highly recommended
     for better standards compliance.  For better compatibility with legacy scripts, such as many Debian
     maintainer scripts, Upstart and SYSV init scripts, and other unfixed scripts, using the compile-time
     options for enabling both set -o posix -o sh when the shell is run as sh is recommended.

     lksh tries to make a cross between a legacy bourne/posix compatibl-ish shell and a legacy pdksh-alike but
     “legacy” is not exactly specified.

     The set built-in command does not currently have all options one would expect from a full-blown mksh or
     pdksh.

     Talk to the MirOS development team using the mailing list at <miros-mksh@mirbsd.org> or the #!/bin/mksh (or
     #ksh) IRC channel at irc.freenode.net (Port 6697 SSL, 6667 unencrypted) if you need any further quirks or
     assistance, and consider migrating your legacy scripts to work with mksh instead of requiring lksh.