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LKSH(1) | General Commands Manual | LKSH(1) |
NAME¶
lksh
—
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; usemksh
instead. - The
KSH_VERSION
string identifieslksh
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 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 $((2147483647 + 1))
... is permitted to, e.g. delete all files on your system (the figure differs for non-32-bit systems, the rule doesn't). The sign of the result of a modulo operation with at least one negative operand is unspecified. Shift operations on negative numbers are unspecified. Division of the largest negative number by -1 is Undefined Behaviour. The compiler is permitted to delete all data and crash the system if Undefined Behaviour occurs (see above for an example).
- The rotation arithmetic operators are not available.
- The shift arithmetic operators take all bits of the second operand into account; if they exceed permitted precision, the result is unspecified.
- The GNU
bash
extension &> to redirect stdout and stderr in one go is not parsed. - The
mksh
command line option-T
is not available. - Unless
set -o posix
is active,lksh
always uses traditional mode for constructs like:$ 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 andlksh
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)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
.
November 11, 2016 | MirBSD |