lksh — Legacy Korn shell built on mksh

Caveats

       To  use  lksh  as  /bin/sh,  compilation  to  enable  set-oposix  by  default if called as sh (adding
       -DMKSH_BINSHPOSIX to CPPFLAGS) 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,  also adding the -DMKSH_BINSHREDUCED compile-time option to
       enable bothset-oposix-osh when the shell  is  run  as  sh,  as  well  as  integrating  the  optional
       disrecommended printf(1) builtin, might be necessary.

       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.

       Talk to the MirBSD development team and users using the mailing list at <miros-mksh@mirbsd.org> or in the
       #!/bin/mksh  IRC  channel;  mind  the  infos  from http://www.mirbsd.org/mksh-faq.htm#contact for either.
       Consider migrating your legacy scripts to work with mksh instead of requiring lksh.

MirBSD                                           January 5, 2024                                         LKSH(1)

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  objectionable POSIX-mandated behaviour, since the MirBSD Korn Shell
       scripting language is much more consistent.

       Do not use lksh as an interactive or login shell; use mksh instead.

       Note that it's strongly recommended to invoke lksh with -oposix to fully enjoy better  compatibility  to
       the  POSIX  standard  (which  is probably why you use lksh over mksh in the first place); -osh (possibly
       additionally to the above) may be needed for some legacy scripts.

Legacy Mode

lksh currently has the following differences from mksh:

• The KSH_VERSION string identifies lksh as “LEGACYKSH” instead of “MIRBSDKSH”. 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 arithmetic, which has quite a few implications: The data type for arithmetic
operations 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).

• 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.

• Unless set-oposix 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.

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

Name

       lksh — Legacy Korn shell built on mksh

Synopsis

lksh [-+abCefhiklmnprUuvXx] [-+oopt] [-cstring | -s | file [args...]]