V8/usr/man/man1/sh.1

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.TH SH 1
.SH NAME
sh, cd, wait \- shell, the standard command programming language
.SH SYNOPSIS
.B sh
[
.B \-acefiknpstuvx
] [ args ]
.SH DESCRIPTION
.I Sh\^
is a command programming language
that executes commands read from a terminal
or a file.
See
.I Invocation\^
below
for the meaning of arguments to the shell.
.SS Definitions
A
.I blank\^
is a tab or a space.
A
.I name\^
is a sequence of letters, digits, or underscores beginning with a letter
or underscore.
A
.I parameter\^
is a name, a digit, or any of the characters
.BR \(** ,
.BR @ ,
.BR # ,
.BR ? ,
.BR \- ,
.BR $ ,
and
.BR !\\^ .
A
.I word\^
is a sequence of characters and quoted strings, surrounded by blanks or newlines.
.SS Commands
A
.I simple-command\^
is a sequence of
.I words\^
separated by
.IR blanks\^ .
The first word specifies the name of the command to
be executed.
Except as specified below,
the remaining words are passed as arguments
to the invoked command.
The command name is passed as argument 0
(see
.IR exec (2)).
The
.I value\^
of a simple-command is its exit status
if it terminates normally, or (octal) 200+\f2status\^\fP if
it terminates abnormally (see
.IR signal (2)
for a list of
status values).
.PP
A
.I pipeline\^
is a sequence of one or more
.I commands\^
separated by
.BR \(bv .
The standard output of each command but the last
is connected by a
.IR pipe (2)
to the standard input of the next command.
Each command is run as a separate process;
the shell waits for the last command to terminate.
The exit status of a pipeline is the exit status of the last command.
.PP
A
.I list\^
is a sequence of one or more
pipelines
separated by
.BR ; ,
.BR & ,
.BR && ,
or
.BR \(bv\|\(bv ,
and optionally terminated by
.B ;
or
.BR & .
Of these four symbols,
.B ;
and
.B &
have equal precedence,
which is lower than that of
.B &&
and
.BR \(bv\|\(bv .
The symbols
.B &&
and
.B \(bv\|\(bv
also have equal precedence.
A semicolon
.RB ( ; )
causes sequential execution of the preceding pipeline; an ampersand
.RB ( & )
causes asynchronous execution of the preceding pipeline (i.e., the shell does
.I not\^
wait for that pipeline to finish).
The symbol
.B &&
.RB (\| \(bv\|\(bv \^)
causes the
.I list\^
following it to be executed only if the preceding
pipeline
returns a zero (non-zero) exit status.
An arbitrary number of new-lines may appear in a
.IR list ,
instead of semicolons,
to delimit commands.
.PP
A
.I command\^
is either a simple-command
or one of the following.
Unless otherwise stated,
the value returned by a command is that of the
last simple-command executed in the command.
.PP
.PD 0
.TP
\f3for\fP \f2name\^\fP \*(OK \f3in\fP \f2word\^\fP .\|.\|. \f3;\fP \*(CK \f3do\fP \f2list\^\fP \f3done\fP
Each time a
.B for
command is executed,
.I name\^
is set to the next
.I word\^
taken from the
.B in
.I word\^
list.
If
.BI in " word\^"
\&.\|.\|. \f3;\fP 
is omitted, then
the
.B for
command executes the \f3do\fP \f2list\^\fP once for each positional parameter
that is set
(see
.I "Parameter Substitution\^"
below).
Execution ends when there are no more words in the list.
.TP
\f3case\fP \f2word\^\fP \f3in\fP \*(OK \f2pattern\^\fP \*(OK \(bv \
\f2pattern\^\fP \*(CK .\|.\|. \f3)\fP \f2list\^\fP \f3;;\fP \*(CK .\|.\|. \f3esac\fP
A
.B case
command executes the
.I list\^
associated with the first
.I pattern\^
that matches
.IR word .
The form of the patterns is
the same as that used for
file-name generation (see 
.IR "File Name Generation\^" )
except that a slash, a leading dot, or a dot immediately
following a slash need not be matched explicitly.
.TP
\f3if\fP \f2list\^\fP \f3then\fP \f2list\^\fP \*(OK \
\f3elif\fP \f2list\^\fP \f3then\fP \f2list\^\fP \*(CK .\|.\|. \
\*(OK \f3else\fP \f2list\^\fP \*(CK \f3f\&i\fP
The
.I list\^
following \f3if\fP is executed and,
if it
returns a zero exit status, the
.I list\^
following
the first
.B then
is executed.
Otherwise, the
.I list\^
following \f3elif\fP
is executed and, if its value is zero,
the
.I list\^
following
the next
.B then
is executed.
Failing that, the
.B else
.I list\^
is executed.
If no
.B else
.I list\^
or
.B then
.I list\^
is executed, then the
.B if
command returns a zero exit status.
.TP
\f3while\fP \f2list\^\fP \f3do\fP \f2list\^\fP \f3done\fP
A
.B while
command repeatedly executes the
.B while
.I list\^
and, if the exit status of the last command in the list is zero, executes
the
.B do
.IR list ;
otherwise the loop terminates.
If no commands in the
.B do
.I list\^
are executed, then the
.B while
command returns a zero exit status;
.B until
may be used in place of
.B while
to negate
the loop termination test.
.TP
\f3(\fP\f2list\^\fP\f3)\fP
.br
Execute
.I list\^
in a sub-shell.
.TP
\f3{\fP\f2list\^\fP\f3}\fP
.br
.I list\^
is simply executed.
.TP
\f2name\^\fP \f3() \f2command\fP
Define a function
which is referenced by
.I name\^.
The body of the function
is the
.IR command .
The most useful form of
.I command
is a sequence of commands enclosed by \f3{\fP and \f3}\fP.
Execution of functions is described below (see
.IR Execution\^ ).
.PD
.PP
The following words
are only recognized as the first word of a command and when not quoted:
.if t .RS
.PP
.B
.if n if then else elif fi case esac for while until do done
.if t if  then  else  elif  f\&i  case  esac  for  while  until  do  done
.if t .RE
.SS Comments
A word beginning with
.B #
causes that word and all the following characters up to a new-line
to be ignored.
.SS Command Substitution
The standard output from a command enclosed in
a pair of grave accents (\^\f3\*`\^\*`\fP\^) may be used as part or all
of a word;
trailing new-lines are removed.
.SS Parameter Substitution
The character
.B $
is used to introduce substitutable 
.IR parameters\^ .
There are two types of parameters,
positional and keyword.
If
.I parameter\^
is a digit, it is a positional parameter.
Positional parameters may be assigned values by
.BR set .
Keyword parameters (also known as variables)
may be assigned values by writing:
.RS
.PP
.IB name = value\^
\*(OK
.IB name = value\^
\*(CK .\|.\|.
.RE
.PP
Pattern-matching is not performed on
.IR value .
There cannot be a function and a variable with the same
.IR name\^  .
.PP
.PD 0
.TP
\f3${\fP\f2parameter\^\fP\f3}\fP
The value, if any, of the parameter is substituted.
The braces are required only when
.I parameter\^
is followed by a letter, digit, or underscore
that is not to be interpreted as part of its name.
If
.I parameter\^
is
.B \(**
or
.BR @ ,
all the positional
parameters, starting with
.BR $1 ,
are substituted
(separated by spaces).
Parameter
.B $0
is set from argument zero when the shell
is invoked.
.TP
\f3${\fP\f2parameter\^\fP\f3:\-\fP\f2word\^\fP\f3}\fP
If
.I parameter\^
is set and is non-null, substitute its value;
otherwise substitute
.IR word .
.TP
\f3${\fP\f2parameter\^\fP\f3:=\fP\f2word\^\fP\f3}\fP
If
.I parameter\^
is not set or is null
set it to
.IR word ;
the value of the parameter is substituted.
Positional parameters may not be assigned to
in this way.
.TP
\f3${\fP\f2parameter\^\fP\f3:?\fP\f2word\^\fP\f3}\fP
If
.I parameter\^
is set and is non-null, substitute its value;
otherwise, print
.I word\^
and exit from the shell.
If
.I word\^
is omitted, the message
``parameter null or not set''
is printed.
.TP
\f3${\fP\f2parameter\^\fP\f3:+\fP\f2word\^\fP\f3}\fP
If
.I parameter\^
is set and is non-null, substitute
.IR word ;
otherwise substitute nothing.
.PD
.PP
In the above,
.I word\^
is not evaluated unless it is
to be used as the substituted string,
so that, in the following example,
.B pwd
is executed only if
.B d
is not set or is null:
.RS
.PP
echo \|${d:\-\^\*`\^pwd\^\*`\^}
.RE
.PP
If the colon
.RB ( : )
is omitted from the above expressions, the
shell only checks whether 
.I parameter\^
is set or not.
.PP
The following
parameters
are automatically set by the shell:
.RS
.PD 0
.TP
.B #
The number of positional parameters in decimal.
.TP
.B \-
Flags supplied to the shell on invocation or by
the
.B set
command.
.TP
.B ?
The decimal value returned by the last synchronously executed command.
.TP
.B $
The process number of this shell.
.TP
.B !
The process number of the last background command invoked.
.PD
.RE
.PP
The following
parameters
are used by the shell:
.RS
.PD 0
.TP
.B
.SM HOME
The default argument (home directory) for the
.I cd\^
command.
.TP
.B
.SM PATH
The search path for commands (see
.I Execution\^
below).
.TP
.B
.SM CDPATH
The search path for the
.I cd
command.
.TP
.B
.SM MAIL
If this parameter is set to the name of a mail file
the shell informs the user of the arrival of mail 
in the specified file.
The file is inspected every three minutes.
.TP
.B
.SM HISTORY
If this parameter is set to the name of a writable file,
the shell appends interactive input to the file, for use by the = command (=(1)).
.TP
.SM
.B PS1
Primary prompt string, by default
.RB `` "$ \|" ''.
.TP
.SM
.B PS2
Secondary prompt string, by default
.RB `` "> \|" ''.
.TP
.SM
.B IFS
Internal field separators,
normally
.BR space ,
.BR tab ,
and
.BR new-line .
.PD
.RE
.PP
The shell gives default values to
\f3\s-1PATH\s+1\fP, \f3\s-1PS1\s+1\fP, \f3\s-1PS2\s+1\fP and \f3\s-1IFS\s+1\fP.
.SM
.B HOME
is set by
.IR login (8).
.SS Blank Interpretation
After parameter and command substitution,
the results of substitution are scanned for internal field separator
characters (those found in
.BR \s-1IFS\s+1 )
and split into distinct arguments where such characters are found.
Explicit null arguments (\^\f3"\^"\fP or \f3\*'\^\*'\fP\^) are retained.
Implicit null arguments
(those resulting from
.I parameters\^
that have no values) are removed.
.SS File Name Generation
Following substitution, each command
.I word\^
is scanned for
the characters
.BR \(** ,
.BR ? ,
and
.BR \*(OK .
If one of these characters appears
the word is regarded as a
.IR pattern .
The word is replaced with alphabetically sorted file names that match the pattern.
If no file name is found that matches the pattern,
the word is left unchanged.
The directories
.B .
and
.B ..
(initially or after a
.BR / )
are only matched by patterns beginning
with an explicit period.
The character
.B /
itself must be matched explicitly.
.PP
.PD 0
.RS
.TP
.B \(**
Matches any string, including the null string.
.TP
.B ?
Matches any single character.
.TP
.BR \*(OK .\|.\|.\^ \*(CK
Matches any one of the enclosed characters.
A pair of characters separated by
.B \-
matches any
character lexically between the pair, inclusive.
If the first character following the opening 
``\*(OK''
is a
.RB `` ^ ''
any character not enclosed is matched.
.PD
.RE
.SS Quoting
The following characters have a special meaning to the shell
and cause termination of a word unless quoted:
.RS
.PP
\f3;  &  (  )  \(bv  <  >  new-line  space  tab\fP  {  }
.RE
.PP
(The characters \f3{\fP and \f3}\fP need not be quoted inside a \f3${\^}\fP construction.)
A character may be
.I quoted\^
(i.e., made to stand for itself)
by preceding
it with a
.BR \e .
The pair
.B \enew-line
is ignored.
All characters enclosed between a pair of single quote marks (\^\f3\*'\^\*'\fP\^),
except a single quote,
are quoted.
Inside double quote marks
(\f3"\^"\fP),
parameter and command substitution occurs and
.B \e
quotes the characters
.BR \e ,
.BR \*` ,
\f3"\fP,
and
.BR $ .
.B
"$\(**"
is equivalent to
\f3"$1 \|$2\fP \|.\|.\|.\f3"\fP,
whereas
.B
"$@"
is equivalent to
.B
"$1"\|
.B
"$2"\|
\&.\|.\|.\|.
.SS Prompting
When used interactively,
the shell prompts with the value of
.SM
.B PS1
before reading a command.
If at any time a new-line is typed and further input is needed
to complete a command, the secondary prompt
(i.e., the value of
.BR \s-1PS2\s+1 )
is issued.
.SS Input/Output
Before a command is executed, its input and output
may be redirected using a special notation interpreted by the shell.
The following may appear anywhere in a simple-command
or may precede or follow a
.I command\^
and are
.I not\^
passed on to the invoked command;
substitution occurs before
.I word\^
or
.I digit\^
is used:
.PP
.PD 0
.TP 14
.B <word
Use file
.I word\^
as standard input (file descriptor 0).
.TP
.B >word
Use file
.I word\^
as standard output (file descriptor 1).
If the file does not exist it is created;
otherwise, it is truncated to zero length.
.TP
.B >\h@-.3m@>word
Use file
.I word\^
as standard output.
If the file exists output is appended to it (by first seeking to the end-of-file);
otherwise, the file is created.
.TP
\f3<\h@-.3m@<word\fP
The shell input is read up to a line that is the same as
.IR word ,
or to an end-of-file.
The resulting document becomes
the standard input.
If any character of
.I word\^
is quoted, no interpretation
is placed upon the characters of the document;
otherwise, parameter and command substitution occurs,
(unescaped)
.B \enew-line
is ignored,
and
.B \e
must be used to quote the characters
.BR \e ,
.BR $ ,
.BR \*` ,
and the first character of
.IR word .
.TP
.B <\h@-.1m@&digit
Use the file associated with file descriptor
.I digit\^
as standard input.
Similarly for the standard output using 
.BR >\h@-.1m@&digit .
.TP
.B <\h@-.1m@&\h@-.1m@\-
The standard input is closed.
Similarly for the standard output using
.BR >\h@-.1m@&\h@-.1m@\- .
.PD
.PP
If any of the above is preceded by a digit,
the
file descriptor which will be associated with the file
is that specified
by the digit
(instead of the default 0 or 1).
For example:
.RS
.PP
\&.\|.\|. \|2>&1
.RE
.PP
associates file descriptor 2 with the file currently associated with 
file descriptor 1.
.PP
The order in which redirections are specified is significant.
The shell evaluates redirections left-to-right.
For example:
.RS
.PP
\&.\|.\|. \|1>\f2xxx\^\fP 2>&1
.RE
.PP
first associates file descriptor 1 with file 
.IR xxx\^ .
It associates file descriptor 2 with the file associated with file
descriptor 1 (i.e. 
.IR xxx\^ ).
If the order of redirections were reversed, file descriptor 2 would be associated 
with the terminal (assuming file descriptor 1 had been) and file descriptor 
1 would be associated with file 
.IR xxx\^ .
.PP
If a command is followed by
.B &
the default standard input
for the command
is the empty file
.BR /dev/null .
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by
input/output specifications.
.SS Environment
The
.I environment\^
(see
.IR environ (5))
is a list of name-value pairs that is passed to
an executed program in the same way as a normal argument list.
The shell interacts with the environment in several ways.
On invocation, the shell scans the environment
and creates a
parameter or function
for each name found,
giving it the corresponding value.
If the user modifies the value of any of these
parameters
or creates new parameters,
none of these affects the environment
unless the
.B export
command is used to bind the shell's
parameter
to the environment (see also 
.BR "set -a" ).
A parameter may be removed from the environment
with the
.B unset
command.
The environment seen by any executed command is thus composed
of any unmodified name-value pairs originally inherited by the shell,
minus any pairs removed by
.BR unset ,
plus any modifications or additions,
all of which must be noted in
.B export
commands.
.PP
The environment for any
.I simple-command\^
may be augmented by prefixing it with one or more assignments to
parameters (but not functions).
Thus:
.RS
.PP
\s-1TERM\s+1=450 \|cmd 				and
.br
(export \|\s-1TERM\s+1; \|\s-1TERM\s+1=450; \|cmd)
.RE
.PP
are equivalent (as far as the execution of
.I cmd\^
is concerned).
.PP
If the
.B \-k
flag is set,
.I all\^
keyword arguments are placed in the environment,
even if they occur after the command name.
The following
first prints
.B "a=b c"
then
.BR c :
.PP
.RS
.nf
echo \|a=b \|c
set \|\-k
echo \|a=b \|c
.fi
.RE
.SS Signals
The \s-1INTERRUPT\s+1 and \s-1QUIT\s+1 signals for an invoked
command are ignored if the command is followed by
.BR & ;
otherwise signals have the values
inherited by the shell from its parent,
with the exception of signal 11
(but see also
the
.B trap
command below).
.SS Execution
Each time a command is executed, the above substitutions are
carried out.
If the command name matches one of the 
.I "Special Commands\^"
listed below, it is executed in the shell process.
If the command name does not match a
.IR "Special Command\^" ,
but matches the name of a defined function, the function is executed 
in the shell process
(note how this differs from the execution of shell procedures).
The positional parameters
.BR $1 ,
.BR $2 ,
\&.\|.\|.\|.
are set to the arguments of the function.
If the command name matches neither a
.I "Special Command\^"
nor the name of a defined function,
a new process is created and an attempt is made to
execute the command via
.IR exec (2).
.PP
The shell parameter
.B
.SM PATH
defines the search path for
the directory containing the command.
Alternative directory names are separated by
a colon
.RB ( : ).
The default path is
.B :/bin:/usr/bin
(specifying the current directory,
.BR /bin ,
and
.BR /usr/bin ,
in that order).
Note that the current directory is specified by a null path name,
which can appear immediately after the equal sign
or between the colon delimiters anywhere else in the path list.
If the command name contains a \f3/\fP the search path
is not used.
Otherwise, each directory in the path is
searched for an executable file.
If the file has execute permission but is not an
.B a.out
file,
it is assumed to be a file containing shell commands.
A sub-shell is spawned to read it.
A parenthesized command is also executed in
a sub-shell.
.SS Special Commands
Input/output redirection is permitted for these commands.
File descriptor 1 is the default output location.
.PP
.PD 0
.TP
.B :
No effect; the command does nothing.
A zero exit code is returned.
.br
.TP
.BI ".\| " file\^
Read and execute commands from
.I file\^
and return.
The search path
specified by
.B
.SM PATH
is used to find the directory containing
.IR file .
.TP
\f3builtin\fP \*(OK \f2command\^\fP \*(CK
Execute the built-in special
.I command
(such as
.BR break)
regardless of functions defined with the same name.
.TP
\f3break\fP \*(OK \f2n\^\fP \*(CK
Exit from the enclosing \f3for\fP or
.B while
loop, if any.
If
.I n\^
is specified break
.I n\^
levels.
.TP
\f3continue\fP \*(OK \f2n\^\fP \*(CK
Resume the next iteration of the enclosing
\f3for\fP or
.B while
loop.
If
.I n\^
is specified resume at the
.IR n -th
enclosing loop.
.TP
\f3cd\fP \*(OK \f2arg\^\fP \*(CK
Change the current directory to
.IR arg .
The shell
parameter
.B
.SM HOME
is the default
.IR arg .
The shell parameter
.B
.SM CDPATH
defines the search path for
the directory containing 
.IR arg .
Alternative directory names are separated by
a colon
.RB ( : ).
The default path is
.B <null>
(specifying the current directory).
Note that the current directory is specified by a null path name,
which can appear immediately after the equal sign
or between the colon delimiters anywhere else in the path list.
If 
.I arg
begins with a \f3/\fP the search path
is not used.
Otherwise, each directory in the path is
searched for
.IR arg .
.br
.ne 2.1v
.TP
\f3eval\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
The arguments are read as input
to the shell
and the resulting command(s) executed.
.TP
\f3exec\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
The command specified by
the arguments is executed in place of this shell
without creating a new process.
Input/output arguments may appear and, if no other
arguments are given, cause the shell
input/output to be modified.
.TP
\f3exit\fP \*(OK \f2n\^\fP \*(CK
Causes a shell to exit
with the exit status specified by
.IR n .
If
.I n\^
is omitted the exit status is that of the last command executed
(an end-of-file will also cause the shell to exit.)
.TP
\f3export\fP \*(OK \f2name\^\fP .\|.\|. \*(CK
The given
.IR name s
are marked
for automatic export to the
.I environment\^
of subsequently-executed commands.
If no arguments are given, a list of all
names that are exported in this shell is printed.
.TP
\f3newgrp\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
Equivalent to
.BI "exec newgrp" " arg\^"
\&.\|.\|.\|.
See
.IR newgrp (1)
for usage and description.
.TP
\f3read\fP \*(OK \f2name\^\fP .\|.\|. \*(CK
One line is read from the standard input and
the first
word is assigned to the first
.IR name ,
the second word
to the second
.IR name ,
etc., with leftover words assigned to the last
.IR name .
The return code is 0 unless an end-of-file is encountered.
.TP
\f3return\fP \*(OK \f2n\^\fP \*(CK
Causes a function to exit with the return value specified by
.IR n .
If
.I n 
is omitted, the return status is that of the last command executed.
.TP
\f3set\fP \*(OK \f3\-\-aehknptuvx\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK \*(CK
.RS
.TP
.B \-a
Mark variables which are modified or created for export.
.TP
.B \-e
Exit immediately if a command
exits with a non-zero exit status.
.TP
.B \-f
Disable file name generation
.TP
.B \-k
All keyword arguments are placed in the environment for a command,
not just those that precede the command name.
.TP
.B \-n
Read commands but do not execute them.
.TP
.B \-p
Remove the definitions for all functions imported from the environment,
and set
.B IFS
to blank, tab and newline.
.TP
.B \-t
Exit after reading and executing one command.
.TP
.B \-u
Treat unset variables as an error when substituting.
.TP
.B \-v
Print shell input lines as they are read.
.TP
.B \-x
Print commands and their arguments as they are executed.
.TP
.B \-\-
Do not change any of the flags; useful in setting
.B $1
to
.BR \- .
.PP
Using
.B \+
rather than
.B \-
causes these flags to be turned off.
These flags can also be used upon invocation of the shell.
The current set of flags may be found in
.BR $\- .
The remaining arguments are positional
parameters and are assigned, in order, to
.BR $1 ,
.BR $2 ,
\&.\|.\|.\|.
If no arguments are given the values
of all names are printed.
.RE
.TP
\f3shift\fP \*(OK \f2n\^\fP \*(CK
.br
The positional parameters from
.B $n+1
\&.\|.\|.
are renamed
.B $1
\&.\|.\|.\|.
If
.I n\^
is not given, it is assumed to be 1.
.TP
\f3times\fP
.br
Print the accumulated user and system times for processes
run from the shell.
.TP
\f3trap\fP \*(OK \f2arg\^\fP \*(CK \*(OK \f2n\^\fP \*(CK .\|.\|.
The command
.I arg\^
is to be read and executed when the shell
receives signal(s)
.IR n .
(Note that
.I arg\^
is scanned once when
the trap is set and once when the trap
is taken.)
Trap commands are executed in order of signal number.
Any attempt to set a trap on a signal that
was ignored on entry to the current shell
is ineffective.
An attempt to trap on signal 11 (memory fault) produces an error.
If
.I arg\^
is absent all trap(s)
.I n\^
are reset
to their original values.
If
.I arg\^
is the null
string this signal is ignored by the shell and by the commands
it invokes.
If
.I n\^
is 0 the command
.I arg\^
is executed
on exit from the shell.
The
.B trap
command
with no arguments prints a list
of commands associated with each signal number.
.TP
\f3umask\fP \*(OK \f2nnn\^\fP \*(CK
The user file-creation mask is set to
.I nnn\^
(see
.IR umask (2)).
If
.I nnn\^
is omitted, the current value of the mask is printed.
.TP
\f3unset\fP \*(OK \f2name\^\fP .\|.\|. \*(CK
For each 
.IR name , 
remove the corresponding variable or function.
The variables 
\f3\s-1PATH\s+1\fP, \f3\s-1PS1\s+1\fP, \f3\s-1PS2\s+1\fP and \f3\s-1IFS\s+1\fP
cannot be unset.
.TP
\f3wait\fP \*(OK \f2n\^\fP \*(CK
Wait for the specified process and report its termination status.
If
.I n\^
is not given all currently active child processes are waited for
and the return code is zero.
.TP
\f3whatis\fP \*(OK \fIname\^\fP .\|.\|. \*(CK
For each
.IR name ,
print the associated value as a parameter, function, builtin or executable
binary as appropriate.
In each case, the value is printed in a form that would yield the same
value if typed as input to the shell itself:
parameters are printed as assignments, functions as their definitions,
builtins as calls to
.BR builtin ,
and binaries as their full pathnames.
.PD
.PP
.SS Invocation
If the shell is invoked through
.IR exec (2)
and the first character of argument zero
is
.BR \- ,
commands are initially read from
.BR \s-1$HOME\s+1/.profile ,
if it exists.
Thereafter, commands are read as described below, which
is also the case when the shell is invoked as
.BR /bin/sh .
The flags below are interpreted by the shell on invocation only; Note
that unless the 
.B \-c
or
.B \-s
flag is specified, the first argument is assumed to be the
name of a file containing commands, and the remaining
arguments are passed as positional parameters
to that command file:
.PP
.PD 0
.TP 10
.BI \-c "\| string\^"
If the
.B \-c
flag is present
commands are read from
.IR string .
.TP
.B \-s
If the
.B \-s
flag is present or if no
arguments remain
commands are read from the standard input.
Any remaining arguments specify the positional parameters.
Shell output (except for 
.IR "Special Commands\^" )
is written to file descriptor 2.
.TP
.B \-i
If the
.B \-i
flag is present or
if the shell input and output are attached to a terminal,
this shell is
.IR interactive .
In this case \s-1TERMINATE\s+1 is ignored (so that \f3kill 0\fP
does not kill an interactive shell) and \s-1INTERRUPT\s+1 is caught and ignored
(so that
.B wait
is interruptible).
In all cases, \s-1QUIT\s+1 is ignored by the shell.
.PD
.PP
The remaining flags and arguments are described under the
.B set
command above.
.SH EXIT STATUS
Errors detected by the shell, such as syntax errors,
cause the shell
to return a non-zero exit status.
If the shell is being used non-interactively
execution of the shell file is abandoned.
Otherwise, the shell returns the exit status of
the last command executed (see also the
.B exit
command above).
.SH FILES
\s-1$HOME\s+1/\f3.\fPprofile
.br
/tmp/sh\(**
.br
/dev/null
.SH SEE ALSO
=(1),
cd(1),
echo(1),
newgrp(1),
test(1)
.br
dup(2),
exec(2),
fork(2),
pipe(2),
signal(2),
umask(2),
wait(2),
a.out(5),
environ(5)
.SH BUGS
A function invocation overwrites the arguments of the invoking shell.