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.