-.\" $MirOS: src/bin/mksh/mksh.1,v 1.420 2016/11/11 23:31:36 tg Exp $
+.\" $MirOS: src/bin/mksh/mksh.1,v 1.442 2017/04/12 18:30:58 tg Exp $
.\" $OpenBSD: ksh.1,v 1.160 2015/07/04 13:27:04 feinerer Exp $
.\"-
.\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
-.\" 2010, 2011, 2012, 2013, 2014, 2015, 2016
+.\" 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017
.\" mirabilos <m@mirbsd.org>
.\"
.\" Provided that these terms and disclaimer and all copyright notices
.\" with -mandoc, it might implement .Mx itself, but we want to
.\" use our own definition. And .Dd must come *first*, always.
.\"
-.Dd $Mdocdate: November 11 2016 $
+.Dd $Mdocdate: April 12 2017 $
.\"
.\" Check which macro package we use, and do other -mdoc setup.
.\"
into account all information is first and foremost presented with
.Nm
in mind and should be taken as such.
-.Ss I'm an Android user, so what's mksh?
-.Nm mksh
-is a
-.Ux
-shell / command interpreter, similar to
-.Nm COMMAND.COM
-or
-.Nm CMD.EXE ,
-which has been included with
-.Tn Android Open Source Project
-for a while now.
-Basically, it's a program that runs in a terminal (console window),
-takes user input and runs commands or scripts, which it can also
-be asked to do by other programs, even in the background.
-Any privilege pop-ups you might be encountering are thus not
-.Nm mksh
-issues but questions by some other program utilising it.
+.Ss I use Android, OS/2, etc. so what...?
+Please see the FAQ at the end of this document.
.Ss Invocation
Most builtins can be called directly, for example if a link points from its
name to the shell; not all make sense, have been tested or work at all though.
.Pp
The following command aliases are defined automatically by the shell:
.Bd -literal -offset indent
-autoload=\*(aq\etypeset \-fu\*(aq
-functions=\*(aq\etypeset \-f\*(aq
-hash=\*(aq\ebuiltin alias \-t\*(aq
-history=\*(aq\ebuiltin fc \-l\*(aq
-integer=\*(aq\etypeset \-i\*(aq
-local=\*(aq\etypeset\*(aq
-login=\*(aq\eexec login\*(aq
-nameref=\*(aq\etypeset \-n\*(aq
+autoload=\*(aq\e\ebuiltin typeset \-fu\*(aq
+functions=\*(aq\e\ebuiltin typeset \-f\*(aq
+hash=\*(aq\e\ebuiltin alias \-t\*(aq
+history=\*(aq\e\ebuiltin fc \-l\*(aq
+integer=\*(aq\e\ebuiltin typeset \-i\*(aq
+local=\*(aq\e\ebuiltin typeset\*(aq
+login=\*(aq\e\ebuiltin exec login\*(aq
+nameref=\*(aq\e\ebuiltin typeset \-n\*(aq
nohup=\*(aqnohup \*(aq
-r=\*(aq\ebuiltin fc \-e \-\*(aq
-type=\*(aq\ebuiltin whence \-v\*(aq
+r=\*(aq\e\ebuiltin fc \-e \-\*(aq
+type=\*(aq\e\ebuiltin whence \-v\*(aq
.Ed
.Pp
Tracked aliases allow the shell to remember where it found a particular
.Dq Li \&.
command (see below).
An empty string resulting from a leading or trailing
-colon, or two adjacent colons, is treated as a
+(semi)colon, or two adjacent ones, is treated as a
.Dq Li \&.
(the current directory).
+.It Ev PATHSEP
+A colon (semicolon on OS/2), for the user's convenience.
.It Ev PGRP
The process ID of the shell's process group leader.
.It Ev PIPESTATUS
.Nm
now also supports the following form:
.Bd -literal -offset indent
-PS1=$'\e1\er\e1\ee[7m\e1$PWD\e1\ee[0m\e1\*(Gt '
+PS1=$\*(aq\e1\er\e1\ee[7m\e1$PWD\e1\ee[0m\e1\*(Gt \*(aq
.Ed
.It Ev PS2
Secondary prompt string, by default
The effective user id of the shell.
.El
.Ss Tilde expansion
-Tilde expansion which is done in parallel with parameter substitution, is done
-on words starting with an unquoted
+Tilde expansion, which is done in parallel with parameter substitution,
+is applied to words starting with an unquoted
.Ql \*(TI .
+In parameter assignments (such as those preceding a simple-command or those
+occurring in the arguments of a declaration utility), tilde expansion is done
+after any assignment (i.e. after the equals sign) or after an unquoted colon
+.Pq Ql \&: ;
+login names are also delimited by colons.
+The Korn shell, except in POSIX mode, always expands tildes after unquoted
+equals signs, not just in assignment context (see below), and enables tab
+completion for tildes after all unquoted colons during command line editing.
+.Pp
The characters following the tilde, up to the first
.Ql / ,
if any, are assumed to be a login name.
if any quoting or parameter substitution occurs in the login name, no
substitution is performed.
.Pp
-In parameter assignments
-(such as those preceding a simple-command or those occurring
-in the arguments of
-.Ic alias ,
-.Ic export ,
-.Ic global ,
-.Ic readonly
-and
-.Ic typeset ) ,
-tilde expansion is done after any assignment
-(i.e. after the equals sign)
-or after an unquoted colon
-.Pq Ql \&: ;
-login names are also delimited by colons.
-.Pp
The home directory of previously expanded login names are cached and re-used.
The
.Ic alias Fl d
pipelines are created and in the order they are given, so the following
will print an error with a line number prepended to it:
.Pp
-.D1 $ cat /foo/bar 2\*(Gt&1 \*(Gt/dev/null \*(Ba pr \-n \-t
+.Dl $ cat /foo/bar 2\*(Gt&1 \*(Gt/dev/null \*(Ba pr \-n \-t
.Pp
File descriptors created by I/O redirections are private to the shell.
.Ss Arithmetic expressions
A function can be made to finish immediately using the
.Ic return
command; this may also be used to explicitly specify the exit status.
+Note that when called in a subshell,
+.Ic return
+will only exit that subshell and will not cause the original shell to exit
+a running function (see the
+.Ic while Ns Li \&... Ns Ic read
+loop FAQ below).
.Pp
Functions defined with the
.Ic function
.Nm
commands keeping assignments:
.Pp
-.Ic builtin , global , source , typeset ,
-.Ic wait
+.Ic global , source , typeset
.Pp
Builtins that are not special:
.Pp
.Ic [ , alias , bg , bind ,
-.Ic cat , cd , command , echo ,
-.Ic false , fc , fg , getopts ,
-.Ic jobs , kill , let , print ,
-.Ic pwd , read , realpath , rename ,
-.Ic sleep , suspend , test , true ,
-.Ic ulimit , umask , unalias , whence
+.Ic builtin , cat , cd , command ,
+.Ic echo , false , fc , fg ,
+.Ic getopts , jobs , kill , let ,
+.Ic print , pwd , read , realpath ,
+.Ic rename , sleep , suspend , test ,
+.Ic true , ulimit , umask , unalias ,
+.Ic wait , whence
.Pp
Once the type of command has been determined, any command-line parameter
assignments are performed and exported for the duration of the command.
Any name with a value defines an alias (see
.Sx Aliases
above).
+.Li \&[A\-Za\-z0\-9_!%,@\-]
+are valid in names except they may not begin with a hyphen-minus.
.Pp
When listing aliases, one of two formats is used.
Normally, aliases are listed as
.Ar command .
.Pp
.It Xo
+.Ic \ebuiltin
+.Ar command Op Ar arg ...
+.Xc
+Same as
+.Ic builtin .
+Additionally acts as declaration utility forwarder, i.e. this is a
+declaration utility (see
+.Sx Tilde expansion )
+.No iff Ar command
+is a declaration utility.
+.Pp
+.It Xo
.Ic cat
.Op Fl u
.Op Ar
and secondly, special built-in commands lose their specialness
(i.e. redirection and utility errors do not cause the shell to
exit, and command assignments are not permanent).
+The declaration utility property is not reset.
.Pp
If the
.Fl p
.Ic posix
or
.Ic sh
-option is set or this is a direct builtin call, only the first argument
-is treated as an option, and only if it is exactly
+option is set or this is a direct builtin call or
+.Ic print
+.Fl R ,
+only the first argument is treated as an option, and only if it is exactly
.Dq Li \-n .
Backslash interpretation is disabled.
.Pp
it does pass these file descriptors on.
.Pp
.It Ic exit Op Ar status
-The shell exits with the specified exit status.
+The shell or subshell exits with the specified exit status.
If
.Ar status
is not specified, the exit status is the current value of the
Sets the export attribute of the named parameters.
Exported parameters are passed in the environment to executed commands.
If values are specified, the named parameters are also assigned.
+This is a declaration utility.
.Pp
If no parameters are specified, all parameters with the export attribute
set are printed one per line; either their names, or, if a
.Ev OPTIND
may lead to unexpected results.
.Pp
-.It global Ar ...
+.It Xo
+.Ic global
+.Op Ic +\-aglpnrtUux
+.Oo Fl L Ns Op Ar n
+.No \*(Ba Fl R Ns Op Ar n
+.No \*(Ba Fl Z Ns Op Ar n Oc
+.Op Fl i Ns Op Ar n
+.Oo Ar name
+.Op Ns = Ns Ar value
+.Ar ... Oc
+.Xc
See
-.Ic typeset .
+.Ic typeset Fl g .
+.No Deprecated , Em will
+be removed from a future version of
+.Nm .
.Pp
.It Xo
.Ic hash
the parsing or evaluation of an expression, the exit status is greater than 1.
Since expressions may need to be quoted,
.No \&(( Ar expr No ))
-is syntactic sugar for
-.No "{ let '" Ns Ar expr Ns "'; }" .
-.Pp
-.It Ic let]
-Internally used alias for
-.Ic let .
+is syntactic sugar for:
+.Dl "{ \e\ebuiltin let \*(aq" Ns Ar expr Ns "\*(aq; }"
.Pp
.It Xo
.Ic mknod
.Pp
.It Xo
.Ic print
-.Oo Fl AclNnprsu Ns Oo Ar n Oc \*(Ba
-.Fl R Op Fl en Oc
+.Oo Fl AcelNnprsu Ns Oo Ar n Oc \*(Ba
+.Fl R Op Fl n Oc
.Op Ar argument ...
.Xc
Print the specified argument(s) on the standard output,
separated by spaces, terminated with a newline.
-The C escapes mentioned in
+The escapes mentioned in
.Sx Backslash expansion
above, as well as
.Dq Li \ec ,
built-in utility and the
.Ic select
statement do.
+.It Fl e
+Restore backslash expansion after a previous
+.Fl r .
.It Fl l
Change the output word separator to newline.
.It Fl N
Inhibit backslash expansion.
.It Fl s
Print to the history file instead of standard output.
-.It Fl u Op Ar n
+.It Fl u Ns Op Ar n
Print to the file descriptor
.Ar n Pq defaults to 1 if omitted
instead of standard output.
.Pp
The
.Fl R
-option is used to emulate, to some degree, the
+option mostly emulates the
.Bx
.Xr echo 1
-command which does not process
-.Ql \e
-sequences unless the
-.Fl e
-option is given.
-As above, the
-.Fl n
-option suppresses the trailing newline.
-.Pp
-.It Ic printf Ar format Op Ar arguments ...
-Formatted output.
-Approximately the same as the
-.Xr printf 1 ,
-utility, except it uses the same
-.Sx Backslash expansion
-and I/O code and does not handle floating point as the rest of
-.Nm mksh .
-An external utility is preferred over the builtin.
-This is not normally part of
-.Nm mksh ;
-however, distributors may have added this as builtin as a speed hack.
-Do not use in new code.
+command which does not expand backslashes and interprets
+its first argument as option only if it is exactly
+.Dq Li \-n
+.Pq to suppress the trailing newline .
.Pp
.It Ic pwd Op Fl LP
Print the present working directory.
.Ic read
exits with a non-zero status.
.Pp
-Another handy set of tricks:
-If
-.Ic read
-is run in a loop such as
-.Ic while read foo; do ...; done
-then leading whitespace will be removed (IFS) and backslashes processed.
-You might want to use
-.Ic while IFS= read \-r foo; do ...; done
-for pristine I/O.
-Similarly, when using the
-.Fl a
-option, use of the
-.Fl r
-option might be prudent; the same applies for:
-.Bd -literal -offset indent
-find . \-type f \-print0 \*(Ba& \e
- while IFS= read \-d \*(aq\*(aq \-pr filename; do
- print \-r \-\- "found \*(Lt${filename#./}\*(Gt"
-done
-.Ed
-.Pp
-The inner loop will be executed in a subshell and variable changes
-cannot be propagated if executed in a pipeline:
-.Bd -literal -offset indent
-bar \*(Ba baz \*(Ba while read foo; do ...; done
-.Ed
-.Pp
-Use co-processes instead:
-.Bd -literal -offset indent
-bar \*(Ba baz \*(Ba&
-while read \-p foo; do ...; done
-exec 3\*(Gt&p; exec 3\*(Gt&\-
-.Ed
-.Pp
.It Xo
.Ic readonly
.Op Fl p
.Ar ... Oc
.Xc
Sets the read-only attribute of the named parameters.
+This is a declaration utility.
If values are given,
parameters are set to them before setting the attribute.
Once a parameter is
.It Fl o Ic braceexpand
Enable brace expansion (a.k.a. alternation).
This is enabled by default.
-If disabled, tilde expansion after an equals sign is disabled as a side effect.
.It Fl o Ic emacs
Enable BRL emacs-like command-line editing (interactive shells only); see
.Sx Emacs editing mode .
.It Fl O Ar file
.Ar file Ns 's
owner is the shell's effective user ID.
-.It Fl o Ar option
-Shell
-.Ar option
-is set (see the
-.Ic set
-command above for a list of options).
-As a non-standard extension, if the option starts with a
-.Ql \&! ,
-the test is negated; the test always fails if
-.Ar option
-doesn't exist (so [ \-o foo \-o \-o !foo ] returns true if and only if option
-.Ar foo
-exists).
-The same can be achieved with [ \-o ?foo ] like in
-.At
-.Nm ksh93 .
-.Ar option
-can also be the short flag led by either
-.Ql \-
-or
-.Ql +
-.Pq no logical negation ,
-for example
-.Dq Li \-x
-or
-.Dq Li +x
-instead of
-.Dq Li xtrace .
.It Fl p Ar file
.Ar file
is a named pipe
.It Fl z Ar string
.Ar string
is empty.
+.It Fl v Ar name
+The shell parameter
+.Ar name
+is set.
+.It Fl o Ar option
+Shell
+.Ar option
+is set (see the
+.Ic set
+command above for a list of options).
+As a non-standard extension, if the option starts with a
+.Ql \&! ,
+the test is negated; the test always fails if
+.Ar option
+doesn't exist (so [ \-o foo \-o \-o !foo ] returns true if and only if option
+.Ar foo
+exists).
+The same can be achieved with [ \-o ?foo ] like in
+.At
+.Nm ksh93 .
+.Ar option
+can also be the short flag led by either
+.Ql \-
+or
+.Ql +
+.Pq no logical negation ,
+for example
+.Dq Li \-x
+or
+.Dq Li +x
+instead of
+.Dq Li xtrace .
.It Ar string No = Ar string
Strings are equal.
.It Ar string No == Ar string
A command that exits with a zero value.
.Pp
.It Xo
-.Ic global
-.Oo Op Ic +\-alpnrtUux
-.Op Fl L Ns Op Ar n
-.Op Fl R Ns Op Ar n
-.Op Fl Z Ns Op Ar n
+.Ic typeset
+.Op Ic +\-aglpnrtUux
+.Oo Fl L Ns Op Ar n
+.No \*(Ba Fl R Ns Op Ar n
+.No \*(Ba Fl Z Ns Op Ar n Oc
.Op Fl i Ns Op Ar n
-.No \*(Ba Fl f Op Fl tux Oc
.Oo Ar name
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
.It Xo
.Ic typeset
-.Oo Op Ic +\-alpnrtUux
-.Op Fl LRZ Ns Op Ar n
-.Op Fl i Ns Op Ar n
-.No \*(Ba Fl f Op Fl tux Oc
-.Oo Ar name
-.Op Ns = Ns Ar value
-.Ar ... Oc
+.Fl f Op Fl tux
+.Op Ar name ...
.Xc
Display or set parameter attributes.
+This is a declaration utility.
With no
.Ar name
arguments, parameter attributes are displayed; if no options are used, the
If
.Ar name
arguments are given, the attributes of the named parameters are set
-.Pq Ic \-
+.Pq Ic \&\-
or cleared
-.Pq Ic + .
+.Pq Ic \&+ ;
+inside a function, this will cause the parameters to be created
+(with no value) in the local scope (but see
+.Fl g ) .
Values for parameters may optionally be specified.
For
.Ar name Ns \&[*] ,
-the change affects the entire array, and no value may be specified.
-.Pp
-If
-.Ic typeset
-is used inside a function, any parameters specified are localised.
-This is not done by the otherwise identical
-.Ic global .
-.Em Note :
-This means that
-.Nm No 's Ic global
-command is
-.Em not
-equivalent to other programming languages' as it does not allow a
-function called from another function to access a parameter at truly
-global scope, but only prevents putting an accessed one into local scope.
+the change affects all elements of the array, and no value may be specified.
.Pp
When
.Fl f
.It Fl f
Function mode.
Display or set functions and their attributes, instead of parameters.
+.It Fl g
+Do not cause named parameters to be created in
+the local scope when called inside a function.
.It Fl i Ns Op Ar n
Integer attribute.
.Ar n
Also note that the types of limits available are system
dependent \*(en some systems have only the
.Fl f
-limit.
+limit, or not even that, or can set only the soft limits
.Bl -tag -width 5n
.It Fl a
Display all limits; unless
or opinionated differences can be disabled by using this mode; these are:
.Bl -bullet
.It
-The GNU
+The incompatible GNU
.Nm bash
I/O redirection
.Ic &\*(Gt Ns Ar file
-is no longer supported.
+is not supported.
.It
File descriptors created by I/O redirections are inherited by
child processes.
The
.Nm echo
builtin does not interpret backslashes and only supports the exact option
-.Dq Li \-n .
+.Fl n .
+.It
+Alias expansion with a trailing space only reruns on command words.
+.It
+Tilde expansion follows POSIX instead of Korn shell rules.
.It
-\&... (list is incomplete and may change for R54)
+The exit status of
+.Ic fg
+is always 0.
+.It
+.Ic kill
+.Fl l
+only lists signal names, all in one line.
+.It
+.Ic getopts
+does not accept options with a leading
+.Ql + .
.El
.Ss SH mode
Compatibility mode; intended for use with legacy scripts that
cannot easily be fixed; the changes are as follows:
.Bl -bullet
.It
-The GNU
+The incompatible GNU
.Nm bash
I/O redirection
.Ic &\*(Gt Ns Ar file
-is no longer supported.
+is not supported.
.It
File descriptors created by I/O redirections are inherited by
child processes.
The
.Nm echo
builtin does not interpret backslashes and only supports the exact option
-.Dq Li \-n .
+.Fl n ,
+unless built with
+.Ev \-DMKSH_MIDNIGHTBSD01ASH_COMPAT .
.It
The substitution operations
.Sm off
.Xc
wrongly do not require a parenthesis to be escaped and do not parse extglobs.
.It
-\&... (list is incomplete and may change for R54)
+The getopt construct from
+.Xr lksh 1
+passes through the errorlevel.
+.It
+.Nm sh
+.Fl c
+eats a leading
+.Fl \-
+if built with
+.Ev \-DMKSH_MIDNIGHTBSD01ASH_COMPAT .
.El
.Ss Interactive input line editing
The shell supports three modes of reading command lines from a
.No KILL Pq \*(haU
.Xc
Deletes the entire input line.
-If Ctrl-U should only delete the line up to the cursor, use:
-.Pp
-.D1 $ bind \-m \*(haU='\*(ha[0\*(haK'
.It kill\-region: \*(haW
Deletes the input between the cursor and the mark.
.It Xo kill\-to\-eol:
.Xr utf\-8 7 ,
.Xr mknod 8
.Pp
-.Pa https://www.mirbsd.org/ksh\-chan.htm
+.Pa http://www.mirbsd.org/ksh\-chan.htm
.Rs
.%A Morris Bolsky
.%B "The KornShell Command and Programming Language"
contributors including our users, to improve the shell is appreciated.
See the documentation, web site and CVS for details.
.Pp
+.Nm mksh\-os2
+is developed by
+.An KO Myung-Hun Aq Mt komh@chollian.net .
+.Pp
+.Nm mksh\-w32
+is developed by
+.An Michael Langguth Aq Mt lan@scalaris.com .
+.Pp
The BSD daemon is Copyright \(co Marshall Kirk McKusick.
The complete legalese is at:
-.Pa https://www.mirbsd.org/TaC\-mksh.txt
+.Pa http://www.mirbsd.org/TaC\-mksh.txt
.\"
.\" This boils down to: feel free to use mksh.ico as application icon
.\" or shortcut for mksh or mksh/Win32 or OS/2; distro patches are ok
.\" to protect it or lose it, which McKusick almost did.
.\"
.Sh CAVEATS
-.Nm
-has a different scope model from
-.At
-.Nm ksh ,
-which leads to subtle differences in semantics for identical builtins.
-This can cause issues with a
-.Ic nameref
-to suddenly point to a local variable by accident; fixing this is hard.
-.Pp
-The parts of a pipeline, like below, are executed in subshells.
-Thus, variable assignments inside them are not visible in the
-surrounding execution environment.
-Use co-processes instead.
-.Bd -literal -offset indent
-foo \*(Ba bar \*(Ba read baz # will not change $baz
-foo \*(Ba bar \*(Ba& read \-p baz # will, however, do so
-.Ed
-.Pp
.Nm mksh
provides a consistent 32-bit integer arithmetic implementation, both
signed and unsigned, with sign of the result of a remainder operation
esac
.Ed
In near future, (Unicode) locale tracking will be implemented though.
+.Pp
+See also the FAQ below.
.Sh BUGS
Suspending (using \*(haZ) pipelines like the one below will only suspend
the currently running part of the pipeline; in this example,
.Xr memmove 3 .
.Pp
This document attempts to describe
-.Nm mksh\ R54
+.Nm mksh\ R55
and up,
.\" with vendor patches from insert-your-name-here,
compiled without any options impacting functionality, such as
Please report bugs in
.Nm
to the
-.Mx
-mailing list at
.Aq Mt miros\-mksh@mirbsd.org
+mailing list
or in the
.Li \&#\&!/bin/mksh
.Pq or Li \&#ksh
.Pq Port 6697 SSL, 6667 unencrypted ,
or at:
.Pa https://launchpad.net/mksh
+.Sh FREQUENTLY ASKED QUESTIONS
+This FAQ attempts to document some of the questions users of
+.Nm
+or readers of this manual page may encounter.
+.Ss I'm an Android user, so what's mksh?
+.Nm mksh
+is a
+.Ux
+shell / command interpreter, similar to
+.Nm COMMAND.COM
+or
+.Nm CMD.EXE ,
+which has been included with
+.Tn Android Open Source Project
+for a while now.
+Basically, it's a program that runs in a terminal (console window),
+takes user input and runs commands or scripts, which it can also
+be asked to do by other programs, even in the background.
+Any privilege pop-ups you might be encountering are thus not
+.Nm mksh
+issues but questions by some other program utilising it.
+.Ss "I'm an OS/2 user, what do I need to know?"
+Unlike the native command prompt, the current working directory is,
+for security reasons common on Unix systems which the shell is designed for,
+not in the search path at all; if you really need this, run the command
+.Li PATH=.$PATHSEP$PATH
+or add that to a suitable initialisation file.
+.Pp
+There are two different newline modes for mksh-os2: standard (Unix) mode,
+in which only LF (0A hex) is supported as line separator, and "textmode",
+which also accepts ASCII newlines (CR+LF), like most other tools on OS/2,
+but creating an incompatibility with standard
+.Nm .
+If you compiled mksh from source, you will get the standard Unix mode unless
+.Fl T
+is added during compilation; you will most likely have gotten this shell
+through komh's port on Hobbes, or from his OS/2 Factory on eComStation
+Korea, which uses "textmode", though.
+Most OS/2 users will want to use "textmode" unless they need absolute
+compatibility with Unix
+.Nm .
+.Ss "How do I start mksh on a specific terminal?"
+Normally:
+.Dl mksh \-T/dev/tty2
+.Pp
+However, if you want for it to return (e.g. for an embedded
+system rescue shell), use this on your real console device instead:
+.Dl mksh \-T!/dev/ttyACM0
+.Pp
+.Nm
+can also daemonise (send to the background):
+.Dl mksh \-T\- \-c \*(aqexec cdio lock\*(aq
+.Ss "POSIX says..."
+Run the shell in POSIX mode (and possibly
+.Nm lksh
+instead of
+.Nm mksh ) :
+.Dl set \-o posix
+.Ss "My prompt from <some other shell> does not work!"
+Contact us on the mailing list or on IRC, we'll convert it for you.
+.Ss "Something is going wrong with my while...read loop"
+Most likely, you've encountered the problem in which the shell runs
+all parts of a pipeline as subshell.
+The inner loop will be executed in a subshell and variable changes
+cannot be propagated if run in a pipeline:
+.Bd -literal -offset indent
+bar \*(Ba baz \*(Ba while read foo; do ...; done
+.Ed
+.Pp
+Note that
+.Ic exit
+in the inner loop will only exit the subshell and not the original shell.
+Likewise, if the code is inside a function,
+.Ic return
+in the inner loop will only exit the subshell and won't terminate the function.
+.Pp
+Use co-processes instead:
+.Bd -literal -offset indent
+bar \*(Ba baz \*(Ba&
+while read \-p foo; do ...; done
+exec 3\*(Gt&p; exec 3\*(Gt&\-
+.Ed
+.Pp
+If
+.Ic read
+is run in a loop such as
+.Ic while read foo; do ...; done
+then leading whitespace will be removed (IFS) and backslashes processed.
+You might want to use
+.Ic while IFS= read \-r foo; do ...; done
+for pristine I/O.
+Similarly, when using the
+.Fl a
+option, use of the
+.Fl r
+option might be prudent
+.Pq Dq Li read \-raN\-1 arr \*(Ltfile ;
+the same applies for NUL-terminated lines:
+.Bd -literal -offset indent
+find . \-type f \-print0 \*(Ba& \e
+ while IFS= read \-d \*(aq\*(aq \-pr filename; do
+ print \-r \-\- "found \*(Lt${filename#./}\*(Gt"
+done
+.Ed
+.Pp
+.Ss "What differences in function-local scopes are there?"
+.Nm
+has a different scope model from
+.At
+.Nm ksh ,
+which leads to subtle differences in semantics for identical builtins.
+This can cause issues with a
+.Ic nameref
+to suddenly point to a local variable by accident.
+.Pp
+.Tn GNU
+.Nm bash
+allows unsetting local variables; in
+.Nm ,
+doing so in a function allows back access to the global variable
+(actually the one in the next scope up) with the same name.
+The following code, when run before the function definitions, changes
+the behaviour of
+.Ic unset
+to behave like other shells (the alias can be removed after the definitions):
+.Bd -literal -offset indent
+case ${KSH_VERSION:\-} in
+*MIRBSD\ KSH*\*(Ba*LEGACY\ KSH*)
+ function unset_compat {
+ \e\ebuiltin typeset unset_compat_x
+
+ for unset_compat_x in "$@"; do
+ eval "\e\e\e\ebuiltin unset $unset_compat_x[*]"
+ done
+ }
+ \e\ebuiltin alias unset=unset_compat
+ ;;
+esac
+.Ed
+.Pp
+When a local variable is created (e.g. using
+.Ic local ,
+.Ic typeset ,
+.Ic integer ,
+.Ic \e\ebuiltin typeset )
+it does not, like in other shells, inherit the value from the global
+(next scope up) variable with the same name; it is rather created
+without any value (unset but defined).
+.Ss "I get an error in this regex comparison"
+Use extglobs instead of regexes:
+.Dl "[[ foo =~ (foo\*(Babar).*baz ]] # becomes"
+.Dl "[[ foo = *@(foo\*(Babar)*baz* ]] # instead"
+.Ss "Are there any extensions to avoid?"
+.Tn GNU
+.Nm bash
+supports
+.Dq Li &\*(Gt
+.Pq and Dq Li \*(Ba&
+to redirect both stdout and stderr in one go, but this breaks POSIX
+and Korn Shell syntax; use POSIX redirections instead:
+.Dl "foo \*(Ba& bar \*(Ba& baz &\*(Gtlog # GNU bash"
+.Dl "foo 2\*(Gt&1 \*(Ba bar 2\*(Gt&1 \*(Ba baz \*(Gtlog 2\*(Gt&1 # POSIX"
+.Ss "\*(haL (Ctrl-L) does not clear the screen"
+Use \*(ha[\*(haL (Escape+Ctrl-L) or rebind it:
+.Dl bind \*(aq\*(haL=clear-screen\*(aq
+.Ss "\*(haU (Ctrl-U) clears the entire line"
+If it should only delete the line up to the cursor, use:
+.Dl bind \-m \*(haU=\*(aq\*(ha[0\*(haK\*(aq
+.Ss "Cursor Up behaves differently from zsh"
+Some shells make Cursor Up search in the history only for
+commands starting with what was already entered.
+.Nm
+separates the shortcuts: Cursor Up goes up one command
+and PgUp searches the history as described above.
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