sh.1

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locations of commands.
With no arguments whatsoever,
the
.Ic hash
command prints out the contents of this table.
Entries which have not been looked at since the last
.Ic cd
command are marked with an asterisk; it is possible for these entries
to be invalid.
.Pp
With arguments, the
.Ic hash
command removes the specified commands from the hash table (unless
they are functions) and then locates them.
With the
.Fl v
option, hash prints the locations of the commands as it finds them.
The
.Fl r
option causes the hash command to delete all the entries in the hash table
except for functions.
.It inputrc Ar file
Read the
.Va file
to set keybindings as defined by
.Xr editrc 5 .
.It jobid Op Ar job
Print the process id's of the processes in the job.
If the
.Ar job
argument is omitted, the current job is used.
.It jobs
This command lists out all the background processes
which are children of the current shell process.
.It pwd Op Fl LP
Print the current directory.
If 
.Fl L
is specified the cached value (initially set from
.Ev PWD )
is checked to see if it refers to the current directory, if it does
the value is printed.
Otherwise the current directory name is found using
.Xr getcwd(3) .
The environment variable
.Ev PWD
is set to printed value.
.Pp
The default is
.Ic pwd
.Fl L ,
but note that the builtin
.Ic cd
command doesn't currently support
.Fl L
or
.Fl P
and will cache (almost) the absolute path.
If
.Ic cd
is changed,
.Ic pwd
may be changed to default to
.Ic pwd
.Fl P .
.Pp
If the current directory is renamed and replaced by a symlink to the
same directory, or the initial
.Ev PWD
value followed a symbolic link, then the cached value may not
be the absolute path.
.Pp
The builtin command may differ from the program of the same name because
the program will use
.Ev PWD
and the builtin uses a separately cached value.
.It Xo read Op Fl p Ar prompt
.Op Fl r
.Ar variable
.Op Ar ...
.Xc
The prompt is printed if the
.Fl p
option is specified and the standard input is a terminal.
Then a line is read from the standard input.
The trailing newline is deleted from the
line and the line is split as described in the section on word splitting
above, and the pieces are assigned to the variables in order.
If there are more pieces than variables, the remaining pieces
(along with the characters in
.Ev IFS
that separated them) are assigned to the last variable.
If there are more variables than pieces,
the remaining variables are assigned the null string.
The
.Ic read
builtin will indicate success unless EOF is encountered on input, in
which case failure is returned.
.Pp
By default, unless the
.Fl r
option is specified, the backslash
.Dq \e
acts as an escape character, causing the following character to be treated
literally.
If a backslash is followed by a newline, the backslash and the
newline will be deleted.
.It readonly Ar name ...
.It readonly Fl p
The specified names are marked as read only, so that they cannot be
subsequently modified or unset.
The shell allows the value of a variable
to be set at the same time it is marked read only by writing
.Pp
.Dl readonly name=value
.Pp
With no arguments the readonly command lists the names of all read only
variables.
With the
.Fl p
option specified the output will be formatted suitably for non-interactive use.
.Pp
.It Xo set
.Oo {
.Fl options | Cm +options | Cm -- }
.Oc Ar arg ...
.Xc
The
.Ic set
command performs three different functions.
.Pp
With no arguments, it lists the values of all shell variables.
.Pp
If options are given, it sets the specified option
flags, or clears them as described in the section called
.Sx Argument List Processing .
.Pp
The third use of the set command is to set the values of the shell's
positional parameters to the specified args.
To change the positional
parameters without changing any options, use
.Dq --
as the first argument to set.
If no args are present, the set command
will clear all the positional parameters (equivalent to executing
.Dq shift $# . )
.It setvar Ar variable Ar value
Assigns value to variable.
(In general it is better to write
variable=value rather than using
.Ic setvar .
.Ic setvar
is intended to be used in
functions that assign values to variables whose names are passed as
parameters.)
.It shift Op Ar n
Shift the positional parameters n times.
A
.Ic shift
sets the value of
.Va $1
to the value of
.Va $2 ,
the value of
.Va $2
to the value of
.Va $3 ,
and so on, decreasing
the value of
.Va $#
by one.
If there are zero positional parameters,
.Ic shift
does nothing.
.It Xo trap
.Op Fl l
.Xc
.It Xo trap
.Op Ar action
.Ar signal ...
.Xc
Cause the shell to parse and execute action when any of the specified
signals are received.
The signals are specified by signal number or as the name of the signal.
If
.Ar signal
is
.Li 0 ,
the action is executed when the shell exits.
.Ar action
may be null, which cause the specified signals to be ignored.
With
.Ar action
omitted or set to `-' the specified signals are set to their default action.
When the shell forks off a subshell, it resets trapped (but not ignored)
signals to the default action.
The
.Ic trap
command has no effect on signals that were
ignored on entry to the shell.
Issuing
.Ic trap
with option
.Ar -l
will print a list of valid signal names.
.Ic trap
without any arguments cause it to write a list of signals and their
associated action to the standard output in a format that is suitable
as an input to the shell that achieves the same trapping results.
.Pp
Examples:
.Pp
.Dl trap
.Pp
List trapped signals and their corresponding action
.Pp
.Dl trap -l
.Pp
Print a list of valid signals
.Pp
.Dl trap '' INT QUIT tstp 30
.Pp
Ignore signals INT QUIT TSTP USR1
.Pp
.Dl trap date INT
.Pp
Print date upon receiving signal INT
.It type Op Ar name ...
Interpret each name as a command and print the resolution of the command
search.
Possible resolutions are:
shell keyword, alias, shell builtin,
command, tracked alias and not found.
For aliases the alias expansion is
printed; for commands and tracked aliases the complete pathname of the
command is printed.
.It ulimit Xo
.Op Fl H \*(Ba Fl S
.Op Fl a \*(Ba Fl tfdscmlpn Op Ar value
.Xc
Inquire about or set the hard or soft limits on processes or set new
limits.
The choice between hard limit (which no process is allowed to
violate, and which may not be raised once it has been lowered) and soft
limit (which causes processes to be signaled but not necessarily killed,
and which may be raised) is made with these flags:
.Bl -tag -width Fl
.It Fl H
set or inquire about hard limits
.It Fl S
set or inquire about soft limits.
If neither
.Fl H
nor
.Fl S
is specified, the soft limit is displayed or both limits are set.
If both are specified, the last one wins.
.El
.Pp
.Bl -tag -width Fl
The limit to be interrogated or set, then, is chosen by specifying
any one of these flags:
.It Fl a
show all the current limits
.It Fl b
show or set the limit on the socket buffer size of a process (in bytes)
.It Fl t
show or set the limit on CPU time (in seconds)
.It Fl f
show or set the limit on the largest file that can be created
(in 512-byte blocks)
.It Fl d
show or set the limit on the data segment size of a process (in kilobytes)
.It Fl s
show or set the limit on the stack size of a process (in kilobytes)
.It Fl c
show or set the limit on the largest core dump size that can be produced
(in 512-byte blocks)
.It Fl m
show or set the limit on the total physical memory that can be
in use by a process (in kilobytes)
.It Fl l
show or set the limit on how much memory a process can lock with
.Xr mlock 2
(in kilobytes)
.It Fl p
show or set the limit on the number of processes this user can
have at one time
.It Fl n
show or set the limit on the number of files a process can have open at once
.El
.Pp
If none of these is specified, it is the limit on file size that is shown
or set.
If value is specified, the limit is set to that number; otherwise
the current limit is displayed.
.Pp
Limits of an arbitrary process can be displayed or set using the
.Xr sysctl 8
utility.
.Pp
.It umask Op Ar mask
Set the value of umask (see
.Xr umask 2 )
to the specified octal value.
If the argument is omitted, the umask value is printed.
.It unalias Xo
.Op Fl a
.Op Ar name
.Xc
If
.Ar name
is specified, the shell removes that alias.
If
.Fl a
is specified, all aliases are removed.
.It unset Ar name ...
The specified variables and functions are unset and unexported.
If a given name corresponds to both a variable and a function, both
the variable and the function are unset.
.It wait Op Ar job
Wait for the specified job to complete and return the exit status of the
last process in the job.
If the argument is omitted, wait for all jobs to
complete and then return an exit status of zero.
.El
.Ss Command Line Editing
When
.Nm
is being used interactively from a terminal, the current command
and the command history (see
.Ic fc
in
.Sx Builtins )
can be edited using emacs-mode or vi-mode command-line editing.
The command
.Ql set -o emacs
enables emacs-mode editing.
The command
.Ql set -o vi
enables vi-mode editing and places sh into vi insert mode.
(See the
.Sx Argument List Processing
section above.)
.Pp
The vi mode uses commands similar to a subset of those described in the
.Xr vi 1
man page.
With vi-mode
enabled, sh can be switched between insert mode and command mode.
It's similar to vi: typing
.Aq ESC
will throw you into command VI command mode.
Hitting
.Aq return
while in command mode will pass the line to the shell.
.Pp
The emacs mode uses commands similar to a subset available in
the emacs editor.
With emacs-mode enabled, special keys can be used to modify the text
in the buffer using the control key.
.Pp
.Nm
uses the
.Xr editline 3
library.
.Sh EXIT STATUS
Errors that are detected by the shell, such as a syntax error, will cause the
shell to exit with a non-zero exit status.
If the shell is not an
interactive shell, the execution of the shell file will be aborted.
Otherwise
the shell will return the exit status of the last command executed, or
if the exit builtin is used with a numeric argument, it will return the
argument.
.Sh ENVIRONMENT
.Bl -tag -width MAILCHECK
.It Ev HOME
Set automatically by
.Xr login 1
from the user's login directory in the password file
.Pq Xr passwd 5 .
This environment variable also functions as the default argument for the
cd builtin.
.It Ev PATH
The default search path for executables.
See the above section
.Sx Path Search .
.It Ev CDPATH
The search path used with the cd builtin.
.It Ev LANG
The string used to specify localization information that allows users
to work with different culture-specific and language conventions.
See
.Xr nls 7 .
.It Ev MAIL
The name of a mail file, that will be checked for the arrival of new mail.
Overridden by
.Ev MAILPATH .
.It Ev MAILCHECK
The frequency in seconds that the shell checks for the arrival of mail
in the files specified by the
.Ev MAILPATH
or the
.Ev MAIL
file.
If set to 0, the check will occur at each prompt.
.It Ev MAILPATH
A colon
.Dq \&:
separated list of file names, for the shell to check for incoming mail.
This environment setting overrides the
.Ev MAIL
setting.
There is a maximum of 10 mailboxes that can be monitored at once.
.It Ev PS1
The primary prompt string, which defaults to
.Dq $ \  ,
unless you are the superuser, in which case it defaults to
.Dq # \  .
.It Ev PS2
The secondary prompt string, which defaults to
.Dq \*[Gt] \  .
.It Ev PS4
Output before each line when execution trace (set -x) is enabled,
defaults to
.Dq + \  .
.It Ev IFS
Input Field Separators.
This is normally set to
.Aq space ,
.Aq tab ,
and
.Aq newline .
See the
.Sx White Space Splitting
section for more details.
.It Ev TERM
The default terminal setting for the shell.
This is inherited by
children of the shell, and is used in the history editing modes.
.It Ev HISTSIZE
The number of lines in the history buffer for the shell.
.El
.Sh FILES
.Bl -item -width HOMEprofilexxxx
.It
.Pa $HOME/.profile
.It
.Pa /etc/profile
.El
.Sh SEE ALSO
.Xr csh 1 ,
.Xr echo 1 ,
.Xr getopt 1 ,
.Xr ksh 1 ,
.Xr login 1 ,
.Xr printf 1 ,
.Xr test 1 ,
.Xr editline 3 ,
.Xr getopt 3 ,
.\" .Xr profile 4 ,
.Xr editrc 5 ,
.Xr passwd 5 ,
.Xr environ 7 ,
.Xr nls 7 ,
.Xr sysctl 8
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .
It was, however, unmaintainable so we wrote this one.
.Sh BUGS
Setuid shell scripts should be avoided at all costs, as they are a
significant security risk.
.Pp
PS1, PS2, and PS4 should be subject to parameter expansion before
being displayed.