.\"	$OpenBSD: sh.1,v 1.99 2014/12/09 15:37:13 schwarze Exp $
.\"
.\"	Public Domain
.\"
.Dd $Mdocdate: December 9 2014 $
.Dt SH 1
.Os
.Sh NAME
.Nm sh
.Nd public domain Bourne shell
.Sh SYNOPSIS
.Nm sh
.Bk -words
.Op Fl +abCefhiklmnpruvXx
.Op Fl +o Ar option
.Op Fl c Ar string \*(Ba Fl s \*(Ba Ar file Op Ar argument ...
.Ek
.Sh DESCRIPTION
.Nm
is a reimplementation of the Bourne shell, a command interpreter for both
interactive and script use.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl c Ar string
.Nm
will execute the command(s) contained in
.Ar string .
.It Fl i
Interactive shell.
A shell is
.Dq interactive
if this
option is used or if both standard input and standard error are attached
to a
.Xr tty 4 .
An interactive shell has job control enabled, ignores the
.Dv SIGINT ,
.Dv SIGQUIT ,
and
.Dv SIGTERM
signals, and prints prompts before reading input (see the
.Ev PS1
and
.Ev PS2
parameters).
For non-interactive shells, the
.Ic trackall
option is on by default (see the
.Ic set
command below).
.It Fl l
Login shell.
If the basename the shell is called with (i.e. argv[0])
starts with
.Ql -
or if this option is used,
the shell is assumed to be a login shell and the shell reads and executes
the contents of
.Pa /etc/profile
and
.Pa $HOME/.profile
if they exist and are readable.
.It Fl p
Privileged shell.
A shell is
.Dq privileged
if this option is used
or if the real user ID or group ID does not match the
effective user ID or group ID (see
.Xr getuid 2
and
.Xr getgid 2 ) .
A privileged shell does not process
.Pa $HOME/.profile
nor the
.Ev ENV
parameter (see below).
Instead, the file
.Pa /etc/suid_profile
is processed.
Clearing the privileged option causes the shell to set
its effective user ID (group ID) to its real user ID (group ID).
.It Fl r
Restricted shell.
A shell is
.Dq restricted
if this
option is used;
if the basename the shell was invoked with was
.Dq rsh ;
or if the
.Ev SHELL
parameter is set to
.Dq rsh .
The following restrictions come into effect after the shell processes any
profile and
.Ev ENV
files:
.Pp
.Bl -bullet -compact
.It
The
.Ic cd
command is disabled.
.It
The
.Ev SHELL ,
.Ev ENV ,
and
.Ev PATH
parameters cannot be changed.
.It
Command names can't be specified with absolute or relative paths.
.It
The
.Fl p
option of the built-in command
.Ic command
can't be used.
.It
Redirections that create files can't be used (i.e.\&
.Ql \*(Gt ,
.Ql \*(Gt\*(Ba ,
.Ql \*(Gt\*(Gt ,
.Ql \*(Lt\*(Gt ) .
.El
.It Fl s
The shell reads commands from standard input; all non-option arguments
are positional parameters.
.El
.Pp
In addition to the above, the options described in the
.Ic set
built-in command can also be used on the command line:
both
.Op Fl +abCefhkmnuvXx
and
.Op Fl +o Ar option
can be used for single letter or long options, respectively.
.Pp
If neither the
.Fl c
nor the
.Fl s
option is specified, the first non-option argument specifies the name
of a file the shell reads commands from.
If there are no non-option
arguments, the shell reads commands from the standard input.
The name of the shell (i.e. the contents of $0)
is determined as follows: if the
.Fl c
option is used and there is a non-option argument, it is used as the name;
if commands are being read from a file, the file is used as the name;
otherwise, the basename the shell was called with (i.e. argv[0]) is used.
.Pp
If the
.Ev ENV
parameter is set when an interactive shell starts (or,
in the case of login shells,
after any profiles are processed), its value is subjected to parameter,
command, arithmetic, and tilde
.Pq Sq ~
substitution and the resulting file
(if any) is read and executed.
.Pp
The exit status of the shell is 127 if the command file specified on the
command line could not be opened, or non-zero if a fatal syntax error
occurred during the execution of a script.
In the absence of fatal errors,
the exit status is that of the last command executed, or zero, if no
command is executed.
.Ss Command syntax
The shell begins parsing its input by breaking it into
.Em words .
Words, which are sequences of characters, are delimited by unquoted whitespace
characters (space, tab, and newline) or meta-characters
.Po
.Ql \*(Lt ,
.Ql \*(Gt ,
.Ql \*(Ba ,
.Ql \&; ,
.Ql \&( ,
.Ql \&) ,
and
.Ql &
.Pc .
Aside from delimiting words, spaces and tabs are ignored, while newlines
usually delimit commands.
The meta-characters are used in building the following
.Em tokens :
.Ql \*(Lt ,
.Ql \*(Lt& ,
.Ql \*(Lt\*(Lt ,
.Ql \*(Gt ,
.Ql \*(Gt& ,
.Ql \*(Gt\*(Gt ,
etc. are used to specify redirections (see
.Sx Input/output redirection
below);
.Ql \*(Ba
is used to create pipelines;
.Ql \&;
is used to separate commands;
.Ql &
is used to create asynchronous pipelines;
.Ql &&
and
.Ql ||
are used to specify conditional execution;
.Ql ;;
is used in
.Ic case
statements;
and lastly,
.Ql \&( .. )\&
is used to create subshells.
.Pp
Whitespace and meta-characters can be quoted individually using a backslash
.Pq Sq \e ,
or in groups using double
.Pq Sq \&"
or single
.Pq Sq '
quotes.
Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves:
.Ql \e ,
.Ql \&" ,
.Ql ' ,
.Ql # ,
.Ql $ ,
.Ql ` ,
.Ql ~ ,
.Ql { ,
.Ql } ,
.Ql * ,
.Ql \&? ,
and
.Ql \&[ .
The first three of these are the above mentioned quoting characters (see
.Sx Quoting
below);
.Ql # ,
if used at the beginning of a word, introduces a comment \(em everything after
the
.Ql #
up to the nearest newline is ignored;
.Ql $
is used to introduce parameter, command, and arithmetic substitutions (see
.Sx Substitution
below);
.Ql `
introduces an old-style command substitution (see
.Sx Substitution
below);
.Ql ~
begins a directory expansion (see
.Sx Tilde expansion
below);
and finally,
.Ql * ,
.Ql \&? ,
and
.Ql \&[
are used in file name generation (see
.Sx File name patterns
below).
.Pp
As words and tokens are parsed, the shell builds commands, of which there
are two basic types:
.Em simple-commands ,
typically programs that are executed, and
.Em compound-commands ,
such as
.Ic for
and
.Ic if
statements, grouping constructs, and function definitions.
.Pp
A simple-command consists of some combination of parameter assignments
(see
.Sx Parameters
below),
input/output redirections (see
.Sx Input/output redirections
below),
and command words; the only restriction is that parameter assignments come
before any command words.
The command words, if any, define the command
that is to be executed and its arguments.
The command may be a shell built-in command, a function,
or an external command
(i.e. a separate executable file that is located using the
.Ev PATH
parameter; see
.Sx Command execution
below).
Note that all command constructs have an exit status: for external commands,
this is related to the status returned by
.Xr wait 2
(if the command could not be found, the exit status is 127; if it could not
be executed, the exit status is 126); the exit status of other command
constructs (built-in commands, functions, compound-commands, pipelines, lists,
etc.) are all well-defined and are described where the construct is
described.
The exit status of a command consisting only of parameter
assignments is that of the last command substitution performed during the
parameter assignment or 0 if there were no command substitutions.
.Pp
Commands can be chained together using the
.Ql |
token to form pipelines, in which the standard output of each command but the
last is piped (see
.Xr pipe 2 )
to the standard input of the following command.
The exit status of a pipeline is that of its last command.
A pipeline may be prefixed by the
.Ql \&!
reserved word, which causes the exit status of the pipeline to be logically
complemented: if the original status was 0, the complemented status will be 1;
if the original status was not 0, the complemented status will be 0.
.Pp
.Em Lists
of commands can be created by separating pipelines by any of the following
tokens:
.Ql && ,
.Ql || ,
.Ql & ,
.Ql |& ,
and
.Ql \&; .
The first two are for conditional execution:
.Dq Ar cmd1 No && Ar cmd2
executes
.Ar cmd2
only if the exit status of
.Ar cmd1
is zero;
.Ql ||
is the opposite \(em
.Ar cmd2
is executed only if the exit status of
.Ar cmd1
is non-zero.
.Ql &&
and
.Ql ||
have equal precedence which is higher than that of
.Ql & ,
.Ql |& ,
and
.Ql \&; ,
which also have equal precedence.
Note that the
.Ql &&
and
.Ql ||
operators are
.Qq left-associative .
For example, both of these commands will print only
.Qq bar :
.Bd -literal -offset indent
$ false && echo foo || echo bar
$ true || echo foo && echo bar
.Ed
.Pp
The
.Ql &
token causes the preceding command to be executed asynchronously; that is,
the shell starts the command but does not wait for it to complete (the shell
does keep track of the status of asynchronous commands; see
.Sx Job control
below).
When an asynchronous command is started when job control is disabled
(i.e. in most scripts), the command is started with signals
.Dv SIGINT
and
.Dv SIGQUIT
ignored and with input redirected from
.Pa /dev/null
(however, redirections specified in the asynchronous command have precedence).
Note that a command must follow the
.Ql &&
and
.Ql ||
operators, while it need not follow
.Ql & ,
.Ql |& ,
or
.Ql \&; .
The exit status of a list is that of the last command executed, with the
exception of asynchronous lists, for which the exit status is 0.
.Pp
Compound commands are created using the following reserved words.
These words
are only recognized if they are unquoted and if they are used as the first
word of a command (i.e. they can't be preceded by parameter assignments or
redirections):
.Bd -literal -offset indent
case   esac       in       while   ]]
do     fi         name     !       {
done   for        select   (       }
elif   function   then     )
else   if         until    [[
.Ed
.Pp
.Sy Note :
Some shells (but not this one) execute control structure commands in a
subshell when one or more of their file descriptors are redirected, so any
environment changes inside them may fail.
To be portable, the
.Ic exec
statement should be used instead to redirect file descriptors before the
control structure.
.Pp
In the following compound command descriptions, command lists (denoted as
.Em list )
that are followed by reserved words must end with a semicolon, a newline, or
a (syntactically correct) reserved word.
For example, the following are all valid:
.Bd -literal -offset indent
$ { echo foo; echo bar; }
$ { echo foo; echo bar\*(Ltnewline\*(Gt }
$ { { echo foo; echo bar; } }
.Ed
.Pp
This is not valid:
.Pp
.Dl $ { echo foo; echo bar }
.Bl -tag -width Ds
.It Pq Ar list
Execute
.Ar list
in a subshell.
There is no implicit way to pass environment changes from a
subshell back to its parent.
.It { Ar list ; No }
Compound construct;
.Ar list
is executed, but not in a subshell.
Note that
.Ql {
and
.Ql }
are reserved words, not meta-characters.
.It Xo case Ar word No in
.Oo Op \&(
.Ar \ pattern
.Op \*(Ba Ar pattern
.No ... No )
.Ar list No ;;\ \& Oc ... esac
.Xc
The
.Ic case
statement attempts to match
.Ar word
against a specified
.Ar pattern ;
the
.Ar list
associated with the first successfully matched pattern is executed.
Patterns used in
.Ic case
statements are the same as those used for file name patterns except that the
restrictions regarding
.Ql \&.
and
.Ql /
are dropped.
Note that any unquoted space before and after a pattern is
stripped; any space within a pattern must be quoted.
Both the word and the
patterns are subject to parameter, command, and arithmetic substitution, as
well as tilde substitution.
For historical reasons, open and close braces may be used instead of
.Ic in
and
.Ic esac
e.g.\&
.Ic case $foo { *) echo bar; } .
The exit status of a
.Ic case
statement is that of the executed
.Ar list ;
if no
.Ar list
is executed, the exit status is zero.
.It Xo for Ar name
.Oo in Ar word No ... Oc ;
.No do Ar list ; No done
.Xc
For each
.Ar word
in the specified word list, the parameter
.Ar name
is set to the word and
.Ar list
is executed.
If
.Ic in
is not used to specify a word list, the positional parameters
($1, $2, etc.)\&
are used instead.
For historical reasons, open and close braces may be used instead of
.Ic do
and
.Ic done
e.g.\&
.Ic for i; { echo $i; } .
The exit status of a
.Ic for
statement is the last exit status of
.Ar list ;
if
.Ar list
is never executed, the exit status is zero.
.It Xo if Ar list ;
.No then Ar list ;
.Oo elif Ar list ;
.No then Ar list ; Oc
.No ...
.Oo else Ar list ; Oc
.No fi
.Xc
If the exit status of the first
.Ar list
is zero, the second
.Ar list
is executed; otherwise, the
.Ar list
following the
.Ic elif ,
if any, is executed with similar consequences.
If all the lists following the
.Ic if
and
.Ic elif Ns s
fail (i.e. exit with non-zero status), the
.Ar list
following the
.Ic else
is executed.
The exit status of an
.Ic if
statement is that of non-conditional
.Ar list
that is executed; if no non-conditional
.Ar list
is executed, the exit status is zero.
.It Xo select Ar name
.Oo in Ar word No ... Oc ;
.No do Ar list ; No done
.Xc
The
.Ic select
statement provides an automatic method of presenting the user with a menu and
selecting from it.
An enumerated list of the specified
.Ar word Ns (s)
is printed on standard error, followed by a prompt
.Po
.Ev PS3: normally
.Sq #?\ \&
.Pc .
A number corresponding to one of the enumerated words is then read from
standard input,
.Ar name
is set to the selected word (or unset if the selection is not valid),
.Ev REPLY
is set to what was read (leading/trailing space is stripped), and
.Ar list
is executed.
If a blank line (i.e. zero or more
.Ev IFS
characters) is entered, the menu is reprinted without executing
.Ar list .
.Pp
When
.Ar list
completes, the enumerated list is printed if
.Ev REPLY
is
.Dv NULL ,
the prompt is printed, and so on.
This process continues until an end-of-file
is read, an interrupt is received, or a
.Ic break
statement is executed inside the loop.
If
.Dq in word ...
is omitted, the positional parameters are used
(i.e. $1, $2, etc.).
For historical reasons, open and close braces may be used instead of
.Ic do
and
.Ic done
e.g.\&
.Ic select i; { echo $i; } .
The exit status of a
.Ic select
statement is zero if a
.Ic break
statement is used to exit the loop, non-zero otherwise.
.It Xo until Ar list ;
.No do Ar list ;
.No done
.Xc
This works like
.Ic while ,
except that the body is executed only while the exit status of the first
.Ar list
is non-zero.
.It Xo while Ar list ;
.No do Ar list ;
.No done
.Xc
A
.Ic while
is a pre-checked loop.
Its body is executed as often as the exit status of the first
.Ar list
is zero.
The exit status of a
.Ic while
statement is the last exit status of the
.Ar list
in the body of the loop; if the body is not executed, the exit status is zero.
.It Xo function Ar name
.No { Ar list ; No }
.Xc
Defines the function
.Ar name
(see
.Sx Functions
below).
Note that redirections specified after a function definition are
performed whenever the function is executed, not when the function definition
is executed.
.It Ar name Ns () Ar command
Mostly the same as
.Ic function
(see
.Sx Functions
below).
.It Bq Bq Ar \ \&expression\ \&
Similar to the
.Ic test
and
.Ic \&[ ... \&]
commands (described later), with the following exceptions:
.Bl -bullet -offset indent
.It
Field splitting and file name generation are not performed on arguments.
.It
The
.Fl a
.Pq AND
and
.Fl o
.Pq OR
operators are replaced with
.Ql &&
and
.Ql || ,
respectively.
.It
Operators (e.g.\&
.Sq Fl f ,
.Sq = ,
.Sq \&! )
must be unquoted.
.It
The second operand of the
.Sq !=
and
.Sq =
expressions are patterns (e.g. the comparison
.Ic [[ foobar = f*r ]]
succeeds).
.It
There are two additional binary operators,
.Ql \*(Lt
and
.Ql \*(Gt ,
which return true if their first string operand is less than, or greater than,
their second string operand, respectively.
.It
The single argument form of
.Ic test ,
which tests if the argument has a non-zero length, is not valid; explicit
operators must always be used e.g. instead of
.No \&[ Ar str No \&]
use
.No \&[[ -n Ar str No \&]] .
.It
Parameter, command, and arithmetic substitutions are performed as expressions
are evaluated and lazy expression evaluation is used for the
.Ql &&
and
.Ql ||
operators.
This means that in the following statement,
.Ic $(\*(Lt foo)
is evaluated if and only if the file
.Pa foo
exists and is readable:
.Bd -literal -offset indent
$ [[ -r foo && $(\*(Lt foo) = b*r ]]
.Ed
.El
.El
.Ss Quoting
Quoting is used to prevent the shell from treating characters or words
specially.
There are three methods of quoting.
First,
.Ql \e
quotes the following character, unless it is at the end of a line, in which
case both the
.Ql \e
and the newline are stripped.
Second, a single quote
.Pq Sq '
quotes everything up to the next single quote (this may span lines).
Third, a double quote
.Pq Sq \&"
quotes all characters, except
.Ql $ ,
.Ql `
and
.Ql \e ,
up to the next unquoted double quote.
.Ql $
and
.Ql `
inside double quotes have their usual meaning (i.e. parameter, command, or
arithmetic substitution) except no field splitting is carried out on the
results of double-quoted substitutions.
If a
.Ql \e
inside a double-quoted string is followed by
.Ql \e ,
.Ql $ ,
.Ql ` ,
or
.Ql \&" ,
it is replaced by the second character; if it is followed by a newline, both
the
.Ql \e
and the newline are stripped; otherwise, both the
.Ql \e
and the character following are unchanged.
.Pp
.Sy Note :
See
.Sx POSIX mode
below for a special rule regarding
differences in quoting when the shell is in POSIX mode.
.Ss Aliases
There are two types of aliases: normal command aliases and tracked aliases.
Command aliases are normally used as a short hand for a long or often used
command.
The shell expands command aliases (i.e. substitutes the alias name
for its value) when it reads the first word of a command.
An expanded alias is re-processed to check for more aliases.
If a command alias ends in a
space or tab, the following word is also checked for alias expansion.
The alias expansion process stops when a word that is not an alias is found,
when a quoted word is found, or when an alias word that is currently being
expanded is found.
.Pp
The following command aliases are defined automatically by the shell:
.Bd -literal -offset indent
hash='alias -t'
type='whence -v'
.Ed
.Pp
Tracked aliases allow the shell to remember where it found a particular
command.
The first time the shell does a path search for a command that is
marked as a tracked alias, it saves the full path of the command.
The next
time the command is executed, the shell checks the saved path to see that it
is still valid, and if so, avoids repeating the path search.
Tracked aliases can be listed and created using
.Ic alias -t .
Note that changing the
.Ev PATH
parameter clears the saved paths for all tracked aliases.
If the
.Ic trackall
option is set (i.e.\&
.Ic set -o Ic trackall
or
.Ic set -h ) ,
the shell tracks all commands.
This option is set automatically for non-interactive shells.
For interactive shells, only the following commands are
automatically tracked:
.Xr cat 1 ,
.Xr cc 1 ,
.Xr chmod 1 ,
.Xr cp 1 ,
.Xr date 1 ,
.Xr ed 1 ,
.Xr emacs 1 ,
.Xr grep 1 ,
.Xr ls 1 ,
.Xr mail 1 ,
.Xr make 1 ,
.Xr mv 1 ,
.Xr pr 1 ,
.Xr rm 1 ,
.Xr sed 1 ,
.Xr vi 1 ,
and
.Xr who 1 .
.Ss Substitution
The first step the shell takes in executing a simple-command is to perform
substitutions on the words of the command.
There are three kinds of
substitution: parameter, command, and arithmetic.
Parameter substitutions,
which are described in detail in the next section, take the form
.Pf $ Ns Ar name
or
.Pf ${ Ns Ar ... Ns } ;
command substitutions take the form
.Pf $( Ns Ar command Ns \&)
or
.Pf ` Ns Ar command Ns ` ;
and arithmetic substitutions take the form
.Pf $(( Ns Ar expression Ns )) .
.Pp
If a substitution appears outside of double quotes, the results of the
substitution are generally subject to word or field splitting according to
the current value of the
.Ev IFS
parameter.
The
.Ev IFS
parameter specifies a list of characters which are used to break a string up
into several words; any characters from the set space, tab, and newline that
appear in the
.Ev IFS
characters are called
.Dq IFS whitespace .
Sequences of one or more
.Ev IFS
whitespace characters, in combination with zero or one
.Pf non- Ev IFS
whitespace
characters, delimit a field.
As a special case, leading and trailing
.Ev IFS
whitespace is stripped (i.e. no leading or trailing empty field is created by
it); leading
.Pf non- Ev IFS
whitespace does create an empty field.
.Pp
Example: If
.Ev IFS
is set to
.Dq \*(Ltspace\*(Gt: ,
and VAR is set to
.Dq \*(Ltspace\*(GtA\*(Ltspace\*(Gt:\*(Ltspace\*(Gt\*(Ltspace\*(GtB::D ,
the substitution for $VAR results in four fields:
.Sq A ,
.Sq B ,
.Sq
(an empty field),
and
.Sq D .
Note that if the
.Ev IFS
parameter is set to the
.Dv NULL
string, no field splitting is done; if the parameter is unset, the default
value of space, tab, and newline is used.
.Pp
Also, note that the field splitting applies only to the immediate result of
the substitution.
Using the previous example, the substitution for $VAR:E
results in the fields:
.Sq A ,
.Sq B ,
.Sq ,
and
.Sq D:E ,
not
.Sq A ,
.Sq B ,
.Sq ,
.Sq D ,
and
.Sq E .
This behavior is POSIX compliant, but incompatible with some other shell
implementations which do field splitting on the word which contained the
substitution or use
.Dv IFS
as a general whitespace delimiter.
.Pp
The results of substitution are, unless otherwise specified, also subject to
file name expansion (see the relevant section below).
.Pp
A command substitution is replaced by the output generated by the specified
command, which is run in a subshell.
For
.Pf $( Ns Ar command Ns \&)
substitutions, normal quoting rules are used when
.Ar command
is parsed; however, for the
.Pf ` Ns Ar command Ns `
form, a
.Ql \e
followed by any of
.Ql $ ,
.Ql ` ,
or
.Ql \e
is stripped (a
.Ql \e
followed by any other character is unchanged).
As a special case in command substitutions, a command of the form
.Pf \*(Lt Ar file
is interpreted to mean substitute the contents of
.Ar file .
Note that
.Ic $(\*(Lt foo)
has the same effect as
.Ic $(cat foo) ,
but it is carried out more efficiently because no process is started.
.Pp
.Sy Note :
.Pf $( Ns Ar command Ns \&)
expressions are currently parsed by finding the matching parenthesis,
regardless of quoting.
This should be fixed soon.
.Pp
Arithmetic substitutions are replaced by the value of the specified expression.
For example, the command
.Ic echo $((2+3*4))
prints 14.
See
.Sx Arithmetic expressions
for a description of an expression.
.Ss Parameters
Parameters are shell variables; they can be assigned values and their values
can be accessed using a parameter substitution.
A parameter name is either one
of the special single punctuation or digit character parameters described
below, or a letter followed by zero or more letters or digits
.Po
.Ql _
counts as a letter
.Pc .
Parameter substitutions take the form
.Pf $ Ns Ar name ,
.Pf ${ Ns Ar name Ns } ,
or
.Sm off
.Pf ${ Ar name Oo Ar expr Oc }
.Sm on
where
.Ar name
is a parameter name.
If substitution is performed on a parameter
that is not set, a null string is substituted unless the
.Ic nounset
option
.Po
.Ic set Fl o Ic nounset
or
.Ic set Fl u
.Pc
is set, in which case an error occurs.
.Pp
Parameters can be assigned values in a number of ways.
First, the shell implicitly sets some parameters like
.Ql # ,
.Ql PWD ,
and
.Ql $ ;
this is the only way the special single character parameters are set.
Second, parameters are imported from the shell's environment at startup.
Third, parameters can be assigned values on the command line: for example,
.Ic FOO=bar
sets the parameter
.Dq FOO
to
.Dq bar ;
multiple parameter assignments can be given on a single command line and they
can be followed by a simple-command, in which case the assignments are in
effect only for the duration of the command (such assignments are also
exported; see below for the implications of this).
Note that both the parameter name and the
.Ql =
must be unquoted for the shell to recognize a parameter assignment.
The fourth way of setting a parameter is with the
.Ic export ,
.Ic readonly ,
and
.Ic typeset
commands; see their descriptions in the
.Sx Command execution
section.
Fifth,
.Ic for
loops set parameters as well as the
.Ic getopts ,
.Ic read ,
and
.Ic set -A
commands.
Lastly, parameters can be assigned values using assignment operators
inside arithmetic expressions (see
.Sx Arithmetic expressions
below) or using the
.Sm off
.Pf ${ Ar name No = Ar value No }
.Sm on
form of the parameter substitution (see below).
.Pp
Parameters with the export attribute (set using the
.Ic export
or
.Ic typeset Fl x
commands, or by parameter assignments followed by simple commands) are put in
the environment (see
.Xr environ 7 )
of commands run by the shell as
.Ar name Ns = Ns Ar value
pairs.
The order in which parameters appear in the environment of a command is
unspecified.
When the shell starts up, it extracts parameters and their values
from its environment and automatically sets the export attribute for those
parameters.
.Pp
Modifiers can be applied to the
.Pf ${ Ns Ar name Ns }
form of parameter substitution:
.Bl -tag -width Ds
.Sm off
.It ${ Ar name No :- Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
it is substituted; otherwise,
.Ar word
is substituted.
.Sm off
.It ${ Ar name No :+ Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
.Ar word
is substituted; otherwise, nothing is substituted.
.Sm off
.It ${ Ar name No := Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
it is substituted; otherwise, it is assigned
.Ar word
and the resulting value of
.Ar name
is substituted.
.Sm off
.It ${ Ar name No :? Ar word No }
.Sm on
If
.Ar name
is set and not
.Dv NULL ,
it is substituted; otherwise,
.Ar word
is printed on standard error (preceded by
.Ar name : )
and an error occurs (normally causing termination of a shell script, function,
or script sourced using the
.Sq \&.
built-in).
If
.Ar word
is omitted, the string
.Dq parameter null or not set
is used instead.
.El
.Pp
In the above modifiers, the
.Ql \&:
can be omitted, in which case the conditions only depend on
.Ar name
being set (as opposed to set and not
.Dv NULL ) .
If
.Ar word
is needed, parameter, command, arithmetic, and tilde substitution are performed
on it; if
.Ar word
is not needed, it is not evaluated.
.Pp
The following forms of parameter substitution can also be used:
.Pp
.Bl -tag -width Ds -compact
.It Pf ${# Ns Ar name Ns \&}
The number of positional parameters if
.Ar name
is
.Ql * ,
.Ql @ ,
or not specified; otherwise the length of the string value of parameter
.Ar name .
.Pp
.It Pf ${# Ns Ar name Ns [*]}
.It Pf ${# Ns Ar name Ns [@]}
The number of elements in the array
.Ar name .
.Pp
.Sm off
.It Xo
.Pf ${ Ar name
.Pf # Ar pattern No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf ## Ar pattern No }
.Xc
.Sm on
If
.Ar pattern
matches the beginning of the value of parameter
.Ar name ,
the matched text is deleted from the result of substitution.
A single
.Ql #
results in the shortest match, and two
of them result in the longest match.
.Pp
.Sm off
.It Xo
.Pf ${ Ar name
.Pf % Ar pattern No }
.Xc
.It Xo
.Pf ${ Ar name
.Pf %% Ar pattern No }
.Xc
.Sm on
Like ${..#..} substitution, but it deletes from the end of the value.
.El
.Pp
The following special parameters are implicitly set by the shell and cannot be
set directly using assignments:
.Bl -tag -width "1 ... 9"
.It Ev \&!
Process ID of the last background process started.
If no background processes have been started, the parameter is not set.
.It Ev \&#
The number of positional parameters ($1, $2, etc.).
.It Ev \&$
The PID of the shell, or the PID of the original shell if it is a subshell.
Do
.Em NOT
use this mechanism for generating temporary file names; see
.Xr mktemp 1
instead.
.It Ev -
The concatenation of the current single letter options (see the
.Ic set
command below for a list of options).
.It Ev \&?
The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal,
.Ic $?\&
is set to 128 plus the signal number.
.It Ev 0
The name of the shell, determined as follows:
the first argument to
.Nm
if it was invoked with the
.Fl c
option and arguments were given; otherwise the
.Ar file
argument, if it was supplied;
or else the basename the shell was invoked with (i.e.\&
.Li argv[0] ) .
.Ev $0
is also set to the name of the current script or
the name of the current function, if it was defined with the
.Ic function
keyword (i.e. a Korn shell style function).
.It Ev 1 No ... Ev 9
The first nine positional parameters that were supplied to the shell, function,
or script sourced using the
.Sq \&.
built-in.
Further positional parameters may be accessed using
.Pf ${ Ar number Ns } .
.It Ev *
All positional parameters (except parameter 0) i.e. $1, $2, $3, ...
If used
outside of double quotes, parameters are separate words (which are subjected
to word splitting); if used within double quotes, parameters are separated
by the first character of the
.Ev IFS
parameter (or the empty string if
.Ev IFS
is
.Dv NULL ) .
.It Ev @
Same as
.Ic $* ,
unless it is used inside double quotes, in which case a separate word is
generated for each positional parameter.
If there are no positional parameters, no word is generated.
.Ic $@
can be used to access arguments, verbatim, without losing
.Dv NULL
arguments or splitting arguments with spaces.
.El
.Pp
The following parameters are set and/or used by the shell:
.Bl -tag -width "EXECSHELL"
.It Ev CDPATH
Search path for the
.Ic cd
built-in command.
It works the same way as
.Ev PATH
for those directories not beginning with
.Ql /
in
.Ic cd
commands.
Note that if
.Ev CDPATH
is set and does not contain
.Sq \&.
or contains an empty path, the current directory is not searched.
Also, the
.Ic cd
built-in command will display the resulting directory when a match is found
in any search path other than the empty path.
.It Ev COLUMNS
Set to the number of columns on the terminal or window.
Currently set to the
.Dq cols
value as reported by
.Xr stty 1
if that value is non-zero.
This parameter is used by the
.Ic set -o
and
.Ic kill -l
commands to format information columns.
.It Ev ENV
If this parameter is found to be set after any profile files are executed, the
expanded value is used as a shell startup file.
It typically contains function and alias definitions.
.It Ev ERRNO
Integer value of the shell's
.Va errno
variable.
It indicates the reason the last system call failed.
Not yet implemented.
.It Ev EXECSHELL
If set, this parameter is assumed to contain the shell that is to be used to
execute commands that
.Xr execve 2
fails to execute and which do not start with a
.Dq #! Ns Ar shell
sequence.
.It Ev FCEDIT
The editor used by the
.Ic fc
command (see below).
.It Ev FPATH
Like
.Ev PATH ,
but used when an undefined function is executed to locate the file defining the
function.
It is also searched when a command can't be found using
.Ev PATH .
See
.Sx Functions
below for more information.
.It Ev HOME
The default directory for the
.Ic cd
command and the value substituted for an unqualified
.Ic ~
(see
.Sx Tilde expansion
below).
.It Ev IFS
Internal field separator, used during substitution and by the
.Ic read
command, to split values into distinct arguments; normally set to space, tab,
and newline.
See
.Sx Substitution
above for details.
.Pp
.Sy Note :
This parameter is not imported from the environment when the shell is
started.
.It Ev SH_VERSION
The version of shell and the date the version was created (read-only).
.It Ev LINENO
The line number of the function or shell script that is currently being
executed.
.It Ev LINES
Set to the number of lines on the terminal or window.
.It Ev OLDPWD
The previous working directory.
Unset if
.Ic cd
has not successfully changed directories since the shell started, or if the
shell doesn't know where it is.
.It Ev OPTARG
When using
.Ic getopts ,
it contains the argument for a parsed option, if it requires one.
.It Ev OPTIND
The index of the next argument to be processed when using
.Ic getopts .
Assigning 1 to this parameter causes
.Ic getopts
to process arguments from the beginning the next time it is invoked.
.It Ev PATH
A colon separated list of directories that are searched when looking for
commands and files sourced using the
.Sq \&.
command (see below).
An empty string resulting from a leading or trailing
colon, or two adjacent colons, is treated as a
.Sq \&.
(the current directory).
.It Ev POSIXLY_CORRECT
If set, this parameter causes the
.Ic posix
option to be enabled.
See
.Sx POSIX mode
below.
.It Ev PPID
The process ID of the shell's parent (read-only).
.It Ev PS1
The primary prompt for interactive shells.
Parameter, command, and arithmetic
substitutions are performed.
.Ql \&!
is replaced with the current command number (see the
.Ic fc
command below).
A literal
.Ql \&!
can be put in the prompt by placing
.Ql !!
in
.Ev PS1 .
The default is
.Sq $\ \&
for non-root users,
.Sq #\ \&
for root.
.It Ev PS2
Secondary prompt string, by default
.Sq \*(Gt\ \& ,
used when more input is needed to complete a command.
.It Ev PS4
Used to prefix commands that are printed during execution tracing (see the
.Ic set Fl x
command below).
Parameter, command, and arithmetic substitutions are performed
before it is printed.
The default is
.Sq +\ \& .
.It Ev PWD
The current working directory.
May be unset or
.Dv NULL
if the shell doesn't know where it is.
.It Ev REPLY
Default parameter for the
.Ic read
command if no names are given.
.It Ev TMPDIR
The directory temporary shell files are created in.
If this parameter is not
set, or does not contain the absolute path of a writable directory, temporary
files are created in
.Pa /tmp .
.El
.Ss Tilde expansion
Tilde expansion, which is done in parallel with parameter substitution, is done
on words starting with an unquoted
.Ql ~ .
The characters following the tilde, up to the first
.Ql / ,
if any, are assumed to be a login name.
If the login name is empty,
.Ql + ,
or
.Ql - ,
the value of the
.Ev HOME ,
.Ev PWD ,
or
.Ev OLDPWD
parameter is substituted, respectively.
Otherwise, the password file is
searched for the login name, and the tilde expression is substituted with the
user's home directory.
If the login name is not found in the password file or
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 readonly ,
and
.Ic typeset ) ,
tilde expansion is done after any assignment
(i.e. after the equals sign)
or after an unquoted colon
.Pq Sq \&: ;
login names are also delimited by colons.
.Pp
The home directory of previously expanded login names are cached and re-used.
The
.Ic alias -d
command may be used to list, change, and add to this cache (e.g.\&
.Ic alias -d fac=/usr/local/facilities; cd ~fac/bin ) .
.Ss File name patterns
A file name pattern is a word containing one or more unquoted
.Ql \&? ,
.Ql * ,
.Ql + ,
.Ql @ ,
or
.Ql \&!
characters or
.Dq [..]
sequences.
The shell replaces file
name patterns with the sorted names of all the files that match the pattern
(if no files match, the word is left unchanged).
The pattern elements have the following meaning:
.Bl -tag -width Ds
.It \&?
Matches any single character.
.It \&*
Matches any sequence of characters.
.It [..]
Matches any of the characters inside the brackets.
Ranges of characters can be
specified by separating two characters by a
.Ql -
(e.g.\&
.Dq [a0-9]
matches the letter
.Sq a
or any digit).
In order to represent itself, a
.Ql -
must either be quoted or the first or last character in the character list.
Similarly, a
.Ql \&]
must be quoted or the first character in the list if it is to represent itself
instead of the end of the list.
Also, a
.Ql \&!
appearing at the start of the list has special meaning (see below), so to
represent itself it must be quoted or appear later in the list.
.Pp
Within a bracket expression, the name of a
.Em character class
enclosed in
.Sq [:
and
.Sq :]
stands for the list of all characters belonging to that class.
Supported character classes:
.Bd -literal -offset indent
alnum	cntrl	lower	space
alpha	digit	print	upper
blank	graph	punct	xdigit
.Ed
.Pp
These match characters using the macros specified in
.Xr isalnum 3 ,
.Xr isalpha 3 ,
and so on.
A character class may not be used as an endpoint of a range.
.It [!..]
Like [..],
except it matches any character not inside the brackets.
.Sm off
.It *( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches any string of characters that matches zero or more occurrences of the
specified patterns.
Example: The pattern
.Ic *(foo|bar)
matches the strings
.Dq ,
.Dq foo ,
.Dq bar ,
.Dq foobarfoo ,
etc.
.Sm off
.It +( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches any string of characters that matches one or more occurrences of the
specified patterns.
Example: The pattern
.Ic +(foo|bar)
matches the strings
.Dq foo ,
.Dq bar ,
.Dq foobar ,
etc.
.Sm off
.It ?( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches the empty string or a string that matches one of the specified
patterns.
Example: The pattern
.Ic ?(foo|bar)
only matches the strings
.Dq ,
.Dq foo ,
and
.Dq bar .
.Sm off
.It @( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches a string that matches one of the specified patterns.
Example: The pattern
.Ic @(foo|bar)
only matches the strings
.Dq foo
and
.Dq bar .
.Sm off
.It !( Ar pattern\*(Ba No ...\*(Ba Ar pattern )
.Sm on
Matches any string that does not match one of the specified patterns.
Examples: The pattern
.Ic !(foo|bar)
matches all strings except
.Dq foo
and
.Dq bar ;
the pattern
.Ic !(*)
matches no strings; the pattern
.Ic !(?)*\&
matches all strings (think about it).
.El
.Pp
Note that
.Nm pdksh
currently never matches
.Sq \&.
and
.Sq .. ,
but the original
.Nm ksh ,
Bourne
.Nm sh ,
and bash do, so this may have to change (too bad).
.Pp
Note that none of the above pattern elements match either a period
.Pq Sq \&.
at the start of a file name or a slash
.Pq Sq / ,
even if they are explicitly used in a [..] sequence; also, the names
.Sq \&.
and
.Sq ..
are never matched, even by the pattern
.Sq .* .
.Pp
If the
.Ic markdirs
option is set, any directories that result from file name generation are marked
with a trailing
.Ql / .
.Ss Input/output redirection
When a command is executed, its standard input, standard output, and standard
error (file descriptors 0, 1, and 2, respectively) are normally inherited from
the shell.
Three exceptions to this are commands in pipelines, for which
standard input and/or standard output are those set up by the pipeline,
asynchronous commands created when job control is disabled, for which standard
input is initially set to be from
.Pa /dev/null ,
and commands for which any of the following redirections have been specified:
.Bl -tag -width Ds
.It \*(Gt Ar file
Standard output is redirected to
.Ar file .
If
.Ar file
does not exist, it is created; if it does exist, is a regular file, and the
.Ic noclobber
option is set, an error occurs; otherwise, the file is truncated.
Note that this means the command
.Ic cmd \*(Lt foo \*(Gt foo
will open
.Ar foo
for reading and then truncate it when it opens it for writing, before
.Ar cmd
gets a chance to actually read
.Ar foo .
.It \*(Gt\*(Ba Ar file
Same as
.Ic \*(Gt ,
except the file is truncated, even if the
.Ic noclobber
option is set.
.It \*(Gt\*(Gt Ar file
Same as
.Ic \*(Gt ,
except if
.Ar file
exists it is appended to instead of being truncated.
Also, the file is opened
in append mode, so writes always go to the end of the file (see
.Xr open 2 ) .
.It \*(Lt Ar file
Standard input is redirected from
.Ar file ,
which is opened for reading.
.It \*(Lt\*(Gt Ar file
Same as
.Ic \*(Lt ,
except the file is opened for reading and writing.
.It \*(Lt\*(Lt Ar marker
After reading the command line containing this kind of redirection (called a
.Dq here document ) ,
the shell copies lines from the command source into a temporary file until a
line matching
.Ar marker
is read.
When the command is executed, standard input is redirected from the
temporary file.
If
.Ar marker
contains no quoted characters, the contents of the temporary file are processed
as if enclosed in double quotes each time the command is executed, so
parameter, command, and arithmetic substitutions are performed, along with
backslash
.Pq Sq \e
escapes for
.Ql $ ,
.Ql ` ,
.Ql \e ,
and
.Ql \enewline .
If multiple here documents are used on the same command line, they are saved in
order.
.It \*(Lt\*(Lt- Ar marker
Same as
.Ic \*(Lt\*(Lt ,
except leading tabs are stripped from lines in the here document.
.It \*(Lt& Ar fd
Standard input is duplicated from file descriptor
.Ar fd .
.Ar fd
can be a single digit, indicating the number of an existing file descriptor;
the letter
.Ql p ,
indicating the file descriptor associated with the output of the current
co-process; or the character
.Ql - ,
indicating standard input is to be closed.
.It \*(Gt& Ar fd
Same as
.Ic \*(Lt& ,
except the operation is done on standard output.
.El
.Pp
In any of the above redirections, the file descriptor that is redirected
(i.e. standard input or standard output)
can be explicitly given by preceding the
redirection with a single digit.
Parameter, command, and arithmetic
substitutions, tilde substitutions, and (if the shell is interactive)
file name generation are all performed on the
.Ar file ,
.Ar marker ,
and
.Ar fd
arguments of redirections.
Note, however, that the results of any file name
generation are only used if a single file is matched; if multiple files match,
the word with the expanded file name generation characters is used.
Note
that in restricted shells, redirections which can create files cannot be used.
.Pp
For simple-commands, redirections may appear anywhere in the command; for
compound-commands
.Po
.Ic if
statements, etc.
.Pc ,
any redirections must appear at the end.
Redirections are processed after
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 cat -n
.Ss Arithmetic expressions
Integer arithmetic expressions can be used with the
.Ic let
command, inside $((..)) expressions, inside array references (e.g.\&
.Ar name Ns Bq Ar expr ) ,
as numeric arguments to the
.Ic test
command, and as the value of an assignment to an integer parameter.
.Pp
Expressions may contain alpha-numeric parameter identifiers, array references,
and integer constants and may be combined with the following C operators
(listed and grouped in increasing order of precedence):
.Pp
Unary operators:
.Bd -literal -offset indent
+ - ! ~ ++ --
.Ed
.Pp
Binary operators:
.Bd -literal -offset indent
,
= *= /= %= += -= \*(Lt\*(Lt= \*(Gt\*(Gt= &= ^= \*(Ba=
\*(Ba\*(Ba
&&
\*(Ba
^
&
== !=
\*(Lt \*(Lt= \*(Gt= \*(Gt
\*(Lt\*(Lt \*(Gt\*(Gt
+ -
* / %
.Ed
.Pp
Ternary operators:
.Bd -literal -offset indent
?: (precedence is immediately higher than assignment)
.Ed
.Pp
Grouping operators:
.Bd -literal -offset indent
( )
.Ed
.Pp
A parameter that is NULL or unset evaluates to 0.
Integer constants may be specified with arbitrary bases using the notation
.Ar base Ns # Ns Ar number ,
where
.Ar base
is a decimal integer specifying the base, and
.Ar number
is a number in the specified base.
Additionally,
integers may be prefixed with
.Sq 0X
or
.Sq 0x
(specifying base 16)
or
.Sq 0
(base 8)
in all forms of arithmetic expressions,
except as numeric arguments to the
.Ic test
command.
.Pp
The operators are evaluated as follows:
.Bl -tag -width Ds -offset indent
.It unary +
Result is the argument (included for completeness).
.It unary -
Negation.
.It \&!
Logical NOT;
the result is 1 if argument is zero, 0 if not.
.It ~
Arithmetic (bit-wise) NOT.
.It ++
Increment; must be applied to a parameter (not a literal or other expression).
The parameter is incremented by 1.
When used as a prefix operator, the result
is the incremented value of the parameter; when used as a postfix operator, the
result is the original value of the parameter.
.It --
Similar to
.Ic ++ ,
except the parameter is decremented by 1.
.It \&,
Separates two arithmetic expressions; the left-hand side is evaluated first,
then the right.
The result is the value of the expression on the right-hand side.
.It =
Assignment; the variable on the left is set to the value on the right.
.It Xo
.No *= /= += -= \*(Lt\*(Lt=
.No \*(Gt\*(Gt= &= ^= \*(Ba=
.Xc
Assignment operators.
.Sm off
.Ao Ar var Ac Xo
.Aq Ar op
.No = Aq Ar expr
.Xc
.Sm on
is the same as
.Sm off
.Ao Ar var Ac Xo
.No = Aq Ar var
.Aq Ar op
.Aq Ar expr ,
.Xc
.Sm on
with any operator precedence in
.Aq Ar expr
preserved.
For example,
.Dq var1 *= 5 + 3
is the same as specifying
.Dq var1 = var1 * (5 + 3) .
.It \*(Ba\*(Ba
Logical OR;
the result is 1 if either argument is non-zero, 0 if not.
The right argument is evaluated only if the left argument is zero.
.It &&
Logical AND;
the result is 1 if both arguments are non-zero, 0 if not.
The right argument is evaluated only if the left argument is non-zero.
.It \*(Ba
Arithmetic (bit-wise) OR.
.It ^
Arithmetic (bit-wise) XOR
(exclusive-OR).
.It &
Arithmetic (bit-wise) AND.
.It ==
Equal; the result is 1 if both arguments are equal, 0 if not.
.It !=
Not equal; the result is 0 if both arguments are equal, 1 if not.
.It \*(Lt
Less than; the result is 1 if the left argument is less than the right, 0 if
not.
.It \*(Lt= \*(Gt= \*(Gt
Less than or equal, greater than or equal, greater than.
See
.Ic \*(Lt .
.It \*(Lt\*(Lt \*(Gt\*(Gt
Shift left (right); the result is the left argument with its bits shifted left
(right) by the amount given in the right argument.
.It + - * /
Addition, subtraction, multiplication, and division.
.It %
Remainder; the result is the remainder of the division of the left argument by
the right.
The sign of the result is unspecified if either argument is negative.
.It Xo
.Sm off
.Aq Ar arg1 ?
.Aq Ar arg2 :
.Aq Ar arg3
.Sm on
.Xc
If
.Aq Ar arg1
is non-zero, the result is
.Aq Ar arg2 ;
otherwise the result is
.Aq Ar arg3 .
.El
.Ss Functions
Functions are defined using either Korn shell
.Ic function Ar function-name
syntax or the Bourne/POSIX shell
.Ar function-name Ns ()
syntax (see below for the difference between the two forms).
Functions are like
.Li .-scripts
(i.e. scripts sourced using the
.Sq \&.
built-in)
in that they are executed in the current environment.
However, unlike
.Li .-scripts ,
shell arguments (i.e. positional parameters $1, $2, etc.)\&
are never visible inside them.
When the shell is determining the location of a command, functions
are searched after special built-in commands, before regular and
non-regular built-ins, and before the
.Ev PATH
is searched.
.Pp
An existing function may be deleted using
.Ic unset Fl f Ar function-name .
A list of functions can be obtained using
.Ic typeset +f
and the function definitions can be listed using
.Ic typeset -f .
The
.Ic autoload
command (which is an alias for
.Ic typeset -fu )
may be used to create undefined functions: when an undefined function is
executed, the shell searches the path specified in the
.Ev FPATH
parameter for a file with the same name as the function, which, if found, is
read and executed.
If after executing the file the named function is found to
be defined, the function is executed; otherwise, the normal command search is
continued (i.e. the shell searches the regular built-in command table and
.Ev PATH ) .
Note that if a command is not found using
.Ev PATH ,
an attempt is made to autoload a function using
.Ev FPATH
(this is an undocumented feature of the original Korn shell).
.Pp
Functions can have two attributes,
.Dq trace
and
.Dq export ,
which can be set with
.Ic typeset -ft
and
.Ic typeset -fx ,
respectively.
When a traced function is executed, the shell's
.Ic xtrace
option is turned on for the function's duration; otherwise, the
.Ic xtrace
option is turned off.
The
.Dq export
attribute of functions is currently not used.
In the original Korn shell,
exported functions are visible to shell scripts that are executed.
.Pp
Since functions are executed in the current shell environment, parameter
assignments made inside functions are visible after the function completes.
If this is not the desired effect, the
.Ic typeset
command can be used inside a function to create a local parameter.
Note that special parameters (e.g.\&
.Ic \&$$ , $! )
can't be scoped in this way.
.Pp
The exit status of a function is that of the last command executed in the
function.
A function can be made to finish immediately using the
.Ic return
command; this may also be used to explicitly specify the exit status.
.Pp
Functions defined with the
.Ic function
reserved word are treated differently in the following ways from functions
defined with the
.Ic ()
notation:
.Bl -bullet
.It
The $0 parameter is set to the name of the function
(Bourne-style functions leave $0 untouched).
.It
Parameter assignments preceding function calls are not kept in the shell
environment (executing Bourne-style functions will keep assignments).
.It
.Ev OPTIND
is saved/reset and restored on entry and exit from the function so
.Ic getopts
can be used properly both inside and outside the function (Bourne-style
functions leave
.Ev OPTIND
untouched, so using
.Ic getopts
inside a function interferes with using
.Ic getopts
outside the function).
.El
.Pp
In the future, the following differences will also be added:
.Bl -bullet
.It
A separate trap/signal environment will be used during the execution of
functions.
This will mean that traps set inside a function will not affect the
shell's traps and signals that are not ignored in the shell (but may be
trapped) will have their default effect in a function.
.It
The EXIT trap, if set in a function, will be executed after the function
returns.
.El
.Ss POSIX mode
The shell is intended to be POSIX compliant;
however, in some cases, POSIX behaviour is contrary either to
the original Korn shell behaviour or to user convenience.
How the shell behaves in these cases is determined by the state of the
.Ic posix
option
.Pq Ic set -o posix .
If it is on, the POSIX behaviour is followed; otherwise, it is not.
The
.Ic posix
option is set automatically when the shell starts up if the environment
contains the
.Ev POSIXLY_CORRECT
parameter.
The shell can also be compiled so that it is in POSIX mode by default;
however, this is usually not desirable.
.Pp
The following is a list of things that are affected by the state of the
.Ic posix
option:
.Bl -bullet
.It
Reading of
.Ev $ENV :
if not in
.Ic posix
mode, the
.Ev ENV
parameter is not expanded and included when the shell starts.
.It
Occurrences of
.Ic \e\&"
inside double quoted
.Ic `..`
command substitutions.
In POSIX mode, the
.Ic \e\&"
is interpreted when the command is interpreted;
in non-POSIX mode,
the backslash is stripped before the command substitution is interpreted.
For example,
.Ic echo \&"`echo \e\&"hi\e\&"`\&"
produces
.Dq \&"hi\&"
in POSIX mode,
.Dq hi
in non-POSIX mode.
To avoid problems, use the
.Ic $(...)\&
form of command substitution.
.It
.Ic kill -l
output.
In POSIX mode, only signal names are listed (in a single line);
in non-POSIX mode,
signal numbers, names, and descriptions are printed (in columns).
In the future, a new option
.Pq Fl v No perhaps
will be added to distinguish the two behaviours.
.It
.Ic echo
options.
In POSIX mode,
.Fl e
and
.Fl E
are not treated as options, but printed like other arguments;
in non-POSIX mode, these options control the interpretation
of backslash sequences.
.It
.Ic fg
exit status.
In POSIX mode, the exit status is 0 if no errors occur;
in non-POSIX mode, the exit status is that of the last foregrounded job.
.It
.Ic getopts .
In POSIX mode, options must start with a
.Ql - ;
in non-POSIX mode, options can start with either
.Ql -
or
.Ql + .
.It
.Ic set - .
In POSIX mode, this does not clear the
.Ic verbose
or
.Ic xtrace
options; in non-POSIX mode, it does.
.It
.Ic set
exit status.
In POSIX mode, the exit status of
.Ic set
is 0 if there are no errors;
in non-POSIX mode, the exit status is that of any
command substitutions performed in generating the
.Ic set
command.
For example,
.Ic set -- `false`; echo $?\&
prints 0 in POSIX mode, 1 in non-POSIX mode.
This construct is used in most shell scripts that use the old
.Xr getopt 1
command.
.It
Argument expansion of the
.Ic alias ,
.Ic export ,
.Ic readonly ,
and
.Ic typeset
commands.
In POSIX mode, normal argument expansion is done; in non-POSIX mode,
field splitting, file globbing, and (normal) tilde expansion
are turned off, while assignment tilde expansion is turned on.
.It
Signal specification.
In POSIX mode, signals can be specified as digits, only
if signal numbers match POSIX values
(i.e. HUP=1, INT=2, QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15);
in non-POSIX mode, signals can always be digits.
.It
Alias expansion.
In POSIX mode, alias expansion is only carried out when reading command words;
in non-POSIX mode, alias expansion is carried out on any
word following an alias that ended in a space.
For example, the following
.Ic for
loop uses parameter
.Sq i
in POSIX mode and
.Sq j
in non-POSIX mode:
.Bd -literal -offset indent
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done
.Ed
.It
.Ic test .
In POSIX mode, the expression
.Sq Fl t
(preceded by some number of
.Sq \&!
arguments) is always true as it is a non-zero length string;
in non-POSIX mode, it tests if file descriptor 1 is a
.Xr tty 4
(i.e. the
.Ar fd
argument to the
.Fl t
test may be left out and defaults to 1).
.El
.Ss Command execution
After evaluation of command-line arguments, redirections, and parameter
assignments, the type of command is determined: a special built-in, a
function, a regular built-in, or the name of a file to execute found using the
.Ev PATH
parameter.
The checks are made in the above order.
Special built-in commands differ from other commands in that the
.Ev PATH
parameter is not used to find them, an error during their execution can
cause a non-interactive shell to exit, and parameter assignments that are
specified before the command are kept after the command completes.
Just to confuse things, if the
.Ic posix
option is turned off (see the
.Ic set
command below), some special commands are very special in that no field
splitting, file globbing, nor tilde expansion is performed
on arguments that look like assignments.
Regular built-in commands are different only in that the
.Ev PATH
parameter is not used to find them.
.Pp
The original
.Nm ksh
and POSIX differ somewhat in which commands are considered
special or regular:
.Pp
POSIX special commands
.Pp
.Ic \&. , \&: , break , continue ,
.Ic eval , exec , exit , export ,
.Ic readonly , return , set , shift ,
.Ic times , trap , unset
.Pp
Additional
.Nm
special commands
.Pp
.Ic builtin , typeset
.Pp
Very special commands
.Pq when POSIX mode is off
.Pp
.Ic alias , readonly , set , typeset
.Pp
POSIX regular commands
.Pp
.Ic alias , bg , cd , command ,
.Ic false , fc , fg , getopts ,
.Ic jobs , kill , pwd , read ,
.Ic true , umask , unalias , wait
.Pp
Additional
.Nm
regular commands
.Pp
.Ic \&[ , echo , let , print ,
.Ic pwd , test , ulimit , whence
.Pp
In the future, the additional
.Nm
special and regular commands may be treated
differently from the POSIX special and regular commands.
.Pp
Once the type of command has been determined, any command-line parameter
assignments are performed and exported for the duration of the command.
.Pp
The following describes the special and regular built-in commands:
.Pp
.Bl -tag -width Ds -compact
.It Ic \&. Ar file Op Ar arg ...
Execute the commands in
.Ar file
in the current environment.
The file is searched for in the directories of
.Ev PATH .
If arguments are given, the positional parameters may be used to access them
while
.Ar file
is being executed.
If no arguments are given, the positional parameters are
those of the environment the command is used in.
.Pp
.It Ic \&: Op Ar ...
The null command.
Exit status is set to zero.
.Pp
.It Xo Ic alias
.Oo Fl d \*(Ba t Oo Fl r Oc \*(Ba
.Cm +-x Oc
.Op Fl p
.Op Cm +
.Oo Ar name
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
Without arguments,
.Ic alias
lists all aliases.
For any name without a value, the existing alias is listed.
Any name with a value defines an alias (see
.Sx Aliases
above).
.Pp
When listing aliases, one of two formats is used.
Normally, aliases are listed as
.Ar name Ns = Ns Ar value ,
where
.Ar value
is quoted.
If options were preceded with
.Ql + ,
or a lone
.Ql +
is given on the command line, only
.Ar name
is printed.
.Pp
The
.Fl d
option causes directory aliases, which are used in tilde expansion, to be
listed or set (see
.Sx Tilde expansion
above).
.Pp
If the
.Fl p
option is used, each alias is prefixed with the string
.Dq alias\ \& .
.Pp
The
.Fl t
option indicates that tracked aliases are to be listed/set (values specified on
the command line are ignored for tracked aliases).
The
.Fl r
option indicates that all tracked aliases are to be reset.
.Pp
The
.Fl x
option sets
.Pq Ic +x No clears
the export attribute of an alias, or, if no names are given, lists the aliases
with the export attribute (exporting an alias has no effect).
.Pp
.It Ic bg Op Ar job ...
Resume the specified stopped job(s) in the background.
If no jobs are specified,
.Ic %+
is assumed.
See
.Sx Job control
below for more information.
.Pp
.It Ic break Op Ar level
Exit the
.Ar level Ns th
inner-most
.Ic for ,
.Ic until ,
or
.Ic while
loop.
.Ar level
defaults to 1.
.Pp
.It Ic builtin Ar command Op Ar arg ...
Execute the built-in command
.Ar command .
.Pp
.It Xo
.Ic cd
.Op Fl LP
.Op Ar dir
.Xc
Set the working directory to
.Ar dir .
If the parameter
.Ev CDPATH
is set, it lists the search path for the directory containing
.Ar dir .
A
.Dv NULL
path means the current directory.
If
.Ar dir
is found in any component of the
.Ev CDPATH
search path other than the
.Dv NULL
path, the name of the new working directory will be written to standard output.
If
.Ar dir
is missing, the home directory
.Ev HOME
is used.
If
.Ar dir
is
.Ql - ,
the previous working directory is used (see the
.Ev OLDPWD
parameter).
.Pp
If the
.Fl L
option (logical path) is used or if the
.Ic physical
option isn't set (see the
.Ic set
command below), references to
.Sq ..
in
.Ar dir
are relative to the path used to get to the directory.
If the
.Fl P
option (physical path) is used or if the
.Ic physical
option is set,
.Sq ..
is relative to the filesystem directory tree.
The
.Ev PWD
and
.Ev OLDPWD
parameters are updated to reflect the current and old working directory,
respectively.
.Pp
.It Xo
.Ic cd
.Op Fl LP
.Ar old new
.Xc
The string
.Ar new
is substituted for
.Ar old
in the current directory, and the shell attempts to change to the new
directory.
.Pp
.It Xo
.Ic command
.Op Fl p
.Ar cmd
.Op Ar arg ...
.Xc
.Ar cmd
is executed exactly as if
.Ic command
had not been specified, with two exceptions:
firstly,
.Ar cmd
cannot be a shell function;
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).
.Pp
If the
.Fl p
option is given, a default search path is used instead of the current value of
.Ev PATH
(the actual value of the default path is system dependent: on
POSIX-ish systems, it is the value returned by
.Ic getconf CS_PATH ) .
.Pp
.It Ic continue Op Ar level
Jumps to the beginning of the
.Ar level Ns th
inner-most
.Ic for ,
.Ic until ,
or
.Ic while
loop.
.Ar level
defaults to 1.
.Pp
.It Xo
.Ic echo
.Op Fl Een
.Op Ar arg ...
.Xc
Prints its arguments (separated by spaces) followed by a newline, to the
standard output.
The newline is suppressed if any of the arguments contain the
backslash sequence
.Ql \ec .
See the
.Ic print
command below for a list of other backslash sequences that are recognized.
.Pp
The options are provided for compatibility with
.Bx
shell scripts.
The
.Fl n
option suppresses the trailing newline,
.Fl e
enables backslash interpretation (a no-op, since this is normally done), and
.Fl E
suppresses backslash interpretation.
If the
.Ic posix
option is set, only the first argument is treated as an option, and only
if it is exactly
.Dq -n .
.Pp
.It Ic eval Ar command ...
The arguments are concatenated (with spaces between them) to form a single
string which the shell then parses and executes in the current environment.
.Pp
.It Xo
.Ic exec
.Op Ar command Op Ar arg ...
.Xc
The command is executed without forking, replacing the shell process.
.Pp
If no command is given except for I/O redirection, the I/O redirection is
permanent and the shell is
not replaced.
Any file descriptors which are opened or
.Xr dup 2 Ns 'd
in this way are made available to other executed commands (note that the Korn
shell differs here: it does not pass on file descriptors greater than 2).
.Pp
.It Ic exit Op Ar status
The shell exits with the specified exit status.
If
.Ar status
is not specified, the exit status is the current value of the
.Ic $?\&
parameter.
.Pp
.It Xo
.Ic export
.Op Fl p
.Op Ar parameter Ns Op = Ns Ar value
.Xc
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.
.Pp
If no parameters are specified, the names of all parameters with the export
attribute are printed one per line, unless the
.Fl p
option is used, in which case
.Ic export
commands defining all exported parameters, including their values, are printed.
.Pp
.It Ic false
A command that exits with a non-zero status.
.Pp
.It Xo
.Ic fc
.Cm -e - \*(Ba Fl s
.Op Fl g
.Op Ar old Ns = Ns Ar new
.Op Ar prefix
.Xc
Re-execute the selected command (the previous command by default) after
performing the optional substitution of
.Ar old
with
.Ar new .
If
.Fl g
is specified, all occurrences of
.Ar old
are replaced with
.Ar new .
The meaning of
.Cm -e -
and
.Fl s
is identical: re-execute the selected command without invoking an editor.
This command is usually accessed with the predefined
.Ic alias r='fc -e -' .
.Pp
.It Ic fg Op Ar job ...
Resume the specified job(s) in the foreground.
If no jobs are specified,
.Ic %+
is assumed.
See
.Sx Job control
below for more information.
.Pp
.It Xo
.Ic getopts
.Ar optstring name
.Op Ar arg ...
.Xc
Used by shell procedures to parse the specified arguments (or positional
parameters, if no arguments are given) and to check for legal options.
.Ar optstring
contains the option letters that
.Ic getopts
is to recognize.
If a letter is followed by a colon, the option is expected to
have an argument.
Options that do not take arguments may be grouped in a single argument.
If an option takes an argument and the option character is not the
last character of the argument it is found in, the remainder of the argument is
taken to be the option's argument; otherwise, the next argument is the option's
argument.
.Pp
Each time
.Ic getopts
is invoked, it places the next option in the shell parameter
.Ar name
and the index of the argument to be processed by the next call to
.Ic getopts
in the shell parameter
.Ev OPTIND .
If the option was introduced with a
.Ql + ,
the option placed in
.Ar name
is prefixed with a
.Ql + .
When an option requires an argument,
.Ic getopts
places it in the shell parameter
.Ev OPTARG .
.Pp
When an illegal option or a missing option argument is encountered, a question
mark or a colon is placed in
.Ar name
(indicating an illegal option or missing argument, respectively) and
.Ev OPTARG
is set to the option character that caused the problem.
Furthermore, if
.Ar optstring
does not begin with a colon, a question mark is placed in
.Ar name ,
.Ev OPTARG
is unset, and an error message is printed to standard error.
.Pp
When the end of the options is encountered,
.Ic getopts
exits with a non-zero exit status.
Options end at the first (non-option
argument) argument that does not start with a
.Ql - ,
or when a
.Ql --
argument is encountered.
.Pp
Option parsing can be reset by setting
.Ev OPTIND
to 1 (this is done automatically whenever the shell or a shell procedure is
invoked).
.Pp
Warning: Changing the value of the shell parameter
.Ev OPTIND
to a value other than 1, or parsing different sets of arguments without
resetting
.Ev OPTIND ,
may lead to unexpected results.
.Pp
.It Xo
.Ic hash
.Op Fl r
.Op Ar name ...
.Xc
Without arguments, any hashed executable command pathnames are listed.
The
.Fl r
option causes all hashed commands to be removed from the hash table.
Each
.Ar name
is searched as if it were a command name and added to the hash table if it is
an executable command.
.Pp
.It Xo
.Ic jobs
.Op Fl lnp
.Op Ar job ...
.Xc
Display information about the specified job(s); if no jobs are specified, all
jobs are displayed.
The
.Fl n
option causes information to be displayed only for jobs that have changed
state since the last notification.
If the
.Fl l
option is used, the process ID of each process in a job is also listed.
The
.Fl p
option causes only the process group of each job to be printed.
See
.Sx Job control
below for the format of
.Ar job
and the displayed job.
.Pp
.It Xo
.Ic kill
.Oo Fl s Ar signame \*(Ba
.No - Ns Ar signum \*(Ba
.No - Ns Ar signame Oc
.No { Ar job \*(Ba pid \*(Ba pgrp No }
.Ar ...
.Xc
Send the specified signal to the specified jobs, process IDs, or process
groups.
If no signal is specified, the
.Dv TERM
signal is sent.
If a job is specified, the signal is sent to the job's process group.
See
.Sx Job control
below for the format of
.Ar job .
.Pp
.It Xo
.Ic kill
.Fl l
.Op Ar exit-status ...
.Xc
Print the signal name corresponding to
.Ar exit-status .
If no arguments are specified, a list of all the signals, their numbers, and
a short description of them are printed.
.Pp
.It Xo
.Ic print
.Oo
.Fl nrsu Ns Oo Ar n Oc \*(Ba
.Fl R Op Fl en
.Oc
.Op Ar argument ...
.Xc
.Ic print
prints its arguments on the standard output, separated by spaces and
terminated with a newline.
The
.Fl n
option suppresses the newline.
By default, certain C escapes are translated.
These include
.Ql \eb ,
.Ql \ef ,
.Ql \en ,
.Ql \er ,
.Ql \et ,
.Ql \ev ,
and
.Ql \e0###
.Po
.Ql #
is an octal digit, of which there may be 0 to 3
.Pc .
.Ql \ec
is equivalent to using the
.Fl n
option.
.Ql \e
expansion may be inhibited with the
.Fl r
option.
The
.Fl s
option prints to the history file instead of standard output; and the
.Fl u
option prints to file descriptor
.Ar n
.Po
.Ar n
defaults to 1 if omitted
.Pc .
.Pp
The
.Fl R
option is used to emulate, to some degree, 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 pwd Op Fl LP
Print the present working directory.
If the
.Fl L
option is used or if the
.Ic physical
option isn't set (see the
.Ic set
command below), the logical path is printed (i.e. the path used to
.Ic cd
to the current directory).
If the
.Fl P
option (physical path) is used or if the
.Ic physical
option is set, the path determined from the filesystem (by following
.Sq ..
directories to the root directory) is printed.
.Pp
.It Xo
.Ic read
.Op Fl rsu Ns Op Ar n
.Op Ar parameter ...
.Xc
Reads a line of input from the standard input, separates the line into fields
using the
.Ev IFS
parameter (see
.Sx Substitution
above), and assigns each field to the specified parameters.
If there are more parameters than fields, the extra parameters are set to
.Dv NULL ,
or alternatively, if there are more fields than parameters, the last parameter
is assigned the remaining fields (inclusive of any separating spaces).
If no parameters are specified, the
.Ev REPLY
parameter is used.
If the input line ends in a backslash and the
.Fl r
option was not used, the backslash and the newline are stripped and more input
is read.
If no input is read,
.Ic read
exits with a non-zero status.
.Pp
The first parameter may have a question mark and a string appended to it, in
which case the string is used as a prompt (printed to standard error before
any input is read) if the input is a
.Xr tty 4
(e.g.\&
.Ic read nfoo?'number of foos: ' ) .
.Pp
The
.Fl u Ns Ar n
option causes input to be read from file descriptor
.Ar n
.Pf ( Ar n
defaults to 0 if omitted).
If the
.Fl s
option is used, input is saved to the history file.
.Pp
.It Xo
.Ic readonly
.Op Fl p
.Oo Ar parameter
.Op Ns = Ns Ar value
.Ar ... Oc
.Xc
Sets the read-only attribute of the named parameters.
If values are given,
parameters are set to them before setting the attribute.
Once a parameter is
made read-only, it cannot be unset and its value cannot be changed.
.Pp
If no parameters are specified, the names of all parameters with the read-only
attribute are printed one per line, unless the
.Fl p
option is used, in which case
.Ic readonly
commands defining all read-only parameters, including their values, are
printed.
.Pp
.It Ic return Op Ar status
Returns from a function or
.Ic .\&
script, with exit status
.Ar status .
If no
.Ar status
is given, the exit status of the last executed command is used.
If used outside of a function or
.Ic .\&
script, it has the same effect as
.Ic exit .
Note that
.Nm pdksh
treats both profile and
.Ev ENV
files as
.Ic .\&
scripts, while the original Korn shell only treats profiles as
.Ic .\&
scripts.
.Pp
.It Xo
.Ic set Op Ic +-abCefhkmnpsuvXx
.Op Ic +-o Ar option
.Op Ic +-A Ar name
.Op Fl -
.Op Ar arg ...
.Xc
The
.Ic set
command can be used to set
.Pq Ic -
or clear
.Pq Ic +
shell options, set the positional parameters, or set an array parameter.
Options can be changed using the
.Cm +-o Ar option
syntax, where
.Ar option
is the long name of an option, or using the
.Cm +- Ns Ar letter
syntax, where
.Ar letter
is the option's single letter name (not all options have a single letter name).
The following table lists both option letters (if they exist) and long names
along with a description of what the option does:
.Bl -tag -width 15n
.It Fl A Ar name
Sets the elements of the array parameter
.Ar name
to
.Ar arg ...
If
.Fl A
is used, the array is reset (i.e. emptied) first; if
.Ic +A
is used, the first N elements are set (where N is the number of arguments);
the rest are left untouched.
.It Fl a \*(Ba Ic allexport
All new parameters are created with the export attribute.
.It Fl b \*(Ba Ic notify
Print job notification messages asynchronously, instead of just before the
prompt.
Only used if job control is enabled
.Pq Fl m .
.It Fl C \*(Ba Ic noclobber
Prevent \*(Gt redirection from overwriting existing files.
Instead, \*(Gt\*(Ba must be used to force an overwrite.
.It Fl e \*(Ba Ic errexit
Exit (after executing the
.Dv ERR
trap) as soon as an error occurs or a command fails (i.e. exits with a
non-zero status).
This does not apply to commands whose exit status is
explicitly tested by a shell construct such as
.Ic if ,
.Ic until ,
.Ic while ,
or
.Ic !\&
statements.
For
.Ic &&
or
.Ic || ,
only the status of the last command is tested.
.It Fl f \*(Ba Ic noglob
Do not expand file name patterns.
.It Fl h \*(Ba Ic trackall
Create tracked aliases for all executed commands (see
.Sx Aliases
above).
Enabled by default for non-interactive shells.
.It Fl k \*(Ba Ic keyword
Parameter assignments are recognized anywhere in a command.
.It Fl m \*(Ba Ic monitor
Enable job control (default for interactive shells).
.It Fl n \*(Ba Ic noexec
Do not execute any commands.
Useful for checking the syntax of scripts
(ignored if interactive).
.It Fl p \*(Ba Ic privileged
The shell is a privileged shell.
It is set automatically if, when the shell starts,
the real UID or GID does not match
the effective UID (EUID) or GID (EGID), respectively.
See above for a description of what this means.
.It Fl s \*(Ba Ic stdin
If used when the shell is invoked, commands are read from standard input.
Set automatically if the shell is invoked with no arguments.
.Pp
When
.Fl s
is used with the
.Ic set
command it causes the specified arguments to be sorted before assigning them to
the positional parameters (or to array
.Ar name ,
if
.Fl A
is used).
.It Fl u \*(Ba Ic nounset
Referencing of an unset parameter is treated as an error, unless one of the
.Ql - ,
.Ql + ,
or
.Ql =
modifiers is used.
.It Fl v \*(Ba Ic verbose
Write shell input to standard error as it is read.
.It Fl X \*(Ba Ic markdirs
Mark directories with a trailing
.Ql /
during file name generation.
.It Fl x \*(Ba Ic xtrace
Print commands and parameter assignments when they are executed, preceded by
the value of
.Ev PS4 .
.It Ic bgnice
Background jobs are run with lower priority.
.It Ic ignoreeof
The shell will not exit when end-of-file is read;
.Ic exit
must be used.
.It Ic interactive
The shell is an interactive shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
.It Ic login
The shell is a login shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
.It Ic nohup
Do not kill running jobs with a
.Dv SIGHUP
signal when a login shell exits.
Currently set by default, but this will
change in the future to be compatible with the original Korn shell (which
doesn't have this option, but does send the
.Dv SIGHUP
signal).
.It Ic nolog
No effect.
In the original Korn shell, this prevents function definitions from
being stored in the history file.
.It Ic physical
Causes the
.Ic cd
and
.Ic pwd
commands to use
.Dq physical
(i.e. the filesystem's)
.Sq ..
directories instead of
.Dq logical
directories (i.e. the shell handles
.Sq .. ,
which allows the user to be oblivious of symbolic links to directories).
Clear by default.
Note that setting this option does not affect the current value of the
.Ev PWD
parameter; only the
.Ic cd
command changes
.Ev PWD .
See the
.Ic cd
and
.Ic pwd
commands above for more details.
.It Ic posix
Enable POSIX mode.
See
.Sx POSIX mode
above.
.It Ic restricted
The shell is a restricted shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
.It Ic vi
Enable
.Xr vi 1 Ns -like
command-line editing (interactive shells only).
.It Ic vi-esccomplete
In vi command-line editing, do command and file name completion when escape
(^[) is entered in command mode.
.It Ic vi-show8
Prefix characters with the eighth bit set with
.Sq M- .
If this option is not set, characters in the range 128\-160 are printed as is,
which may cause problems.
.It Ic vi-tabcomplete
In vi command-line editing, do command and file name completion when tab (^I)
is entered in insert mode.
.It Ic viraw
No effect.
In the original Korn shell, unless
.Ic viraw
was set, the vi command-line mode would let the
.Xr tty 4
driver do the work until ESC (^[) was entered.
.Nm pdksh
is always in viraw mode.
.El
.Pp
These options can also be used upon invocation of the shell.
The current set of
options (with single letter names) can be found in the parameter
.Sq $- .
.Ic set Fl o
with no option name will list all the options and whether each is on or off;
.Ic set +o
will print the long names of all options that are currently on.
.Pp
Remaining arguments, if any, are positional parameters and are assigned, in
order, to the positional parameters (i.e. $1, $2, etc.).
If options end with
.Ql --
and there are no remaining arguments, all positional parameters are cleared.
If no options or arguments are given, the values of all names are printed.
For unknown historical reasons, a lone
.Ql -
option is treated specially \- it clears both the
.Fl x
and
.Fl v
options.
.Pp
.It Ic shift Op Ar number
The positional parameters
.Ar number Ns +1 ,
.Ar number Ns +2 ,
etc. are renamed to
.Sq 1 ,
.Sq 2 ,
etc.
.Ar number
defaults to 1.
.Pp
.It Ic test Ar expression
.It Ic \&[ Ar expression Ic \&]
.Ic test
evaluates the
.Ar expression
and returns zero status if true, 1 if false, or greater than 1 if there
was an error.
It is normally used as the condition command of
.Ic if
and
.Ic while
statements.
Symbolic links are followed for all
.Ar file
expressions except
.Fl h
and
.Fl L .
.Pp
The following basic expressions are available:
.Bl -tag -width 17n
.It Fl a Ar file
.Ar file
exists.
.It Fl b Ar file
.Ar file
is a block special device.
.It Fl c Ar file
.Ar file
is a character special device.
.It Fl d Ar file
.Ar file
is a directory.
.It Fl e Ar file
.Ar file
exists.
.It Fl f Ar file
.Ar file
is a regular file.
.It Fl G Ar file
.Ar file Ns 's
group is the shell's effective group ID.
.It Fl g Ar file
.Ar file Ns 's
mode has the setgid bit set.
.It Fl h Ar file
.Ar file
is a symbolic link.
.It Fl k Ar file
.Ar file Ns 's
mode has the
.Xr sticky 8
bit set.
.It Fl L Ar file
.Ar file
is a symbolic link.
.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).
.It Fl p Ar file
.Ar file
is a named pipe.
.It Fl r Ar file
.Ar file
exists and is readable.
.It Fl S Ar file
.Ar file
is a
.Xr unix 4 Ns -domain
socket.
.It Fl s Ar file
.Ar file
is not empty.
.It Fl t Op Ar fd
File descriptor
.Ar fd
is a
.Xr tty 4
device.
If the
.Ic posix
option is not set,
.Ar fd
may be left out, in which case it is taken to be 1 (the behaviour differs due
to the special POSIX rules described above).
.It Fl u Ar file
.Ar file Ns 's
mode has the setuid bit set.
.It Fl w Ar file
.Ar file
exists and is writable.
.It Fl x Ar file
.Ar file
exists and is executable.
.It Ar file1 Fl nt Ar file2
.Ar file1
is newer than
.Ar file2 .
.It Ar file1 Fl ot Ar file2
.Ar file1
is older than
.Ar file2 .
.It Ar file1 Fl ef Ar file2
.Ar file1
is the same file as
.Ar file2 .
.It Ar string
.Ar string
has non-zero length.
.It Fl n Ar string
.Ar string
is not empty.
.It Fl z Ar string
.Ar string
is empty.
.It Ar string No = Ar string
Strings are equal.
.It Ar string No != Ar string
Strings are not equal.
.It Ar number Fl eq Ar number
Numbers compare equal.
.It Ar number Fl ne Ar number
Numbers compare not equal.
.It Ar number Fl ge Ar number
Numbers compare greater than or equal.
.It Ar number Fl gt Ar number
Numbers compare greater than.
.It Ar number Fl le Ar number
Numbers compare less than or equal.
.It Ar number Fl \&lt Ar number
Numbers compare less than.
.El
.Pp
The above basic expressions, in which unary operators have precedence over
binary operators, may be combined with the following operators (listed in
increasing order of precedence):
.Bd -literal -offset indent
expr -o expr		Logical OR.
expr -a expr		Logical AND.
! expr			Logical NOT.
( expr )		Grouping.
.Ed
.Pp
On operating systems not supporting
.Pa /dev/fd/ Ns Ar n
devices (where
.Ar n
is a file descriptor number), the
.Ic test
command will attempt to fake it for all tests that operate on files (except the
.Fl e
test).
For example,
[ -w /dev/fd/2 ] tests if file descriptor 2 is writable.
.Pp
Note that some special rules are applied (courtesy of POSIX)
if the number of
arguments to
.Ic test
or
.Ic \&[ ... \&]
is less than five: if leading
.Ql \&!
arguments can be stripped such that only one argument remains then a string
length test is performed (again, even if the argument is a unary operator); if
leading
.Ql \&!
arguments can be stripped such that three arguments remain and the second
argument is a binary operator, then the binary operation is performed (even
if the first argument is a unary operator, including an unstripped
.Ql \&! ) .
.Pp
.Sy Note :
A common mistake is to use
.Dq if \&[ $foo = bar \&] ,
which fails if parameter
.Dq foo
is
.Dv NULL
or unset, if it has embedded spaces (i.e.\&
.Ev IFS
characters), or if it is a unary operator like
.Sq \&!
or
.Sq Fl n .
Use tests like
.Dq if \&[ \&"X$foo\&" = Xbar \&]
instead.
.Pp
.It Ic times
Print the accumulated user and system times used both by the shell
and by processes that the shell started which have exited.
The format of the output is:
.Bd -literal -offset indent
0m0.00s 0m0.00s
0m0.00s 0m0.00s
.Ed
.Pp
.It Ic trap Op Ar handler signal ...
Sets a trap handler that is to be executed when any of the specified signals are
received.
.Ar handler
is either a
.Dv NULL
string, indicating the signals are to be ignored, a minus sign
.Pq Sq - ,
indicating that the default action is to be taken for the signals (see
.Xr signal 3 ) ,
or a string containing shell commands to be evaluated and executed at the first
opportunity (i.e. when the current command completes, or before printing the
next
.Ev PS1
prompt) after receipt of one of the signals.
.Ar signal
is the name of a signal (e.g.\&
.Dv PIPE
or
.Dv ALRM )
or the number of the signal (see the
.Ic kill -l
command above).
.Pp
There are two special signals:
.Dv EXIT
(also known as 0), which is executed when the shell is about to exit, and
.Dv ERR ,
which is executed after an error occurs (an error is something that would cause
the shell to exit if the
.Fl e
or
.Ic errexit
option were set \- see the
.Ic set
command above).
.Dv EXIT
handlers are executed in the environment of the last executed command.
Note
that for non-interactive shells, the trap handler cannot be changed for signals
that were ignored when the shell started.
.Pp
With no arguments,
.Ic trap
lists, as a series of
.Ic trap
commands, the current state of the traps that have been set since the shell
started.
Note that the output of
.Ic trap
cannot be usefully piped to another process (an artifact of the fact that
traps are cleared when subprocesses are created).
.Pp
The original Korn shell's
.Dv DEBUG
trap and the handling of
.Dv ERR
and
.Dv EXIT
traps in functions are not yet implemented.
.Pp
.It Ic true
A command that exits with a zero value.
.Pp
.It Xo
.Ic typeset
.Oo
.Op Ic +-lprtUux
.Op Fl L Ns Op Ar n
.Op Fl R Ns Op Ar n
.Op Fl Z 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
.Xc
Display or set parameter attributes.
With no
.Ar name
arguments, parameter attributes are displayed; if no options are used, the
current attributes of all parameters are printed as
.Ic typeset
commands; if an option is given (or
.Ql -
with no option letter), all parameters and their values with the specified
attributes are printed; if options are introduced with
.Ql + ,
parameter values are not printed.
.Pp
If
.Ar name
arguments are given, the attributes of the named parameters are set
.Pq Ic -
or cleared
.Pq Ic + .
Values for parameters may optionally be specified.
If
.Ic typeset
is used inside a function, any newly created parameters are local to the
function.
.Pp
When
.Fl f
is used,
.Ic typeset
operates on the attributes of functions.
As with parameters, if no
.Ar name
arguments are given,
functions are listed with their values (i.e. definitions) unless
options are introduced with
.Ql + ,
in which case only the function names are reported.
.Bl -tag -width Ds
.It Fl f
Function mode.
Display or set functions and their attributes, instead of parameters.
.It Fl i Ns Op Ar n
Integer attribute.
.Ar n
specifies the base to use when displaying the integer (if not specified, the
base given in the first assignment is used).
Parameters with this attribute may
be assigned values containing arithmetic expressions.
.It Fl L Ns Op Ar n
Left justify attribute.
.Ar n
specifies the field width.
If
.Ar n
is not specified, the current width of a parameter (or the width of its first
assigned value) is used.
Leading whitespace (and zeros, if used with the
.Fl Z
option) is stripped.
If necessary, values are either truncated or space padded
to fit the field width.
.It Fl l
Lower case attribute.
All upper case characters in values are converted to lower case.
(In the original Korn shell, this parameter meant
.Dq long integer
when used with the
.Fl i
option.)
.It Fl p
Print complete
.Ic typeset
commands that can be used to re-create the attributes (but not the values) of
parameters.
This is the default action (option exists for ksh93 compatibility).
.It Fl R Ns Op Ar n
Right justify attribute.
.Ar n
specifies the field width.
If
.Ar n
is not specified, the current width of a parameter (or the width of its first
assigned value) is used.
Trailing whitespace is stripped.
If necessary, values are either stripped of leading characters or space
padded to make them fit the field width.
.It Fl r
Read-only attribute.
Parameters with this attribute may not be assigned to or unset.
Once this attribute is set, it cannot be turned off.
.It Fl t
Tag attribute.
Has no meaning to the shell; provided for application use.
.Pp
For functions,
.Fl t
is the trace attribute.
When functions with the trace attribute are executed, the
.Ic xtrace
.Pq Fl x
shell option is temporarily turned on.
.It Fl U
Unsigned integer attribute.
Integers are printed as unsigned values (only
useful when combined with the
.Fl i
option).
This option is not in the original Korn shell.
.It Fl u
Upper case attribute.
All lower case characters in values are converted to upper case.
(In the original Korn shell, this parameter meant
.Dq unsigned integer
when used with the
.Fl i
option, which meant upper case letters would never be used for bases greater
than 10.
See the
.Fl U
option.)
.Pp
For functions,
.Fl u
is the undefined attribute.
See
.Sx Functions
above for the implications of this.
.It Fl x
Export attribute.
Parameters (or functions) are placed in the environment of
any executed commands.
Exported functions are not yet implemented.
.It Fl Z Ns Op Ar n
Zero fill attribute.
If not combined with
.Fl L ,
this is the same as
.Fl R ,
except zero padding is used instead of space padding.
.El
.Pp
.It Xo
.Ic ulimit
.Op Fl acdfHlmnpSst Op Ar value
.Ar ...
.Xc
Display or set process limits.
If no options are used, the file size limit
.Pq Fl f
is assumed.
.Ar value ,
if specified, may be either an arithmetic expression starting with a
number or the word
.Dq unlimited .
The limits affect the shell and any processes created by the shell after a
limit is imposed; limits may not be increased once they are set.
.Bl -tag -width 5n
.It Fl a
Display all limits; unless
.Fl H
is used, soft limits are displayed.
.It Fl c Ar n
Impose a size limit of
.Ar n
blocks on the size of core dumps.
.It Fl d Ar n
Impose a size limit of
.Ar n
kilobytes on the size of the data area.
.It Fl f Ar n
Impose a size limit of
.Ar n
blocks on files written by the shell and its child processes (files of any
size may be read).
.It Fl H
Set the hard limit only (the default is to set both hard and soft limits).
.It Fl l Ar n
Impose a limit of
.Ar n
kilobytes on the amount of locked (wired) physical memory.
.It Fl m Ar n
Impose a limit of
.Ar n
kilobytes on the amount of physical memory used.
.It Fl n Ar n
Impose a limit of
.Ar n
file descriptors that can be open at once.
.It Fl p Ar n
Impose a limit of
.Ar n
processes that can be run by the user at any one time.
.It Fl S
Set the soft limit only (the default is to set both hard and soft limits).
.It Fl s Ar n
Impose a size limit of
.Ar n
kilobytes on the size of the stack area.
.It Fl t Ar n
Impose a time limit of
.Ar n
CPU seconds spent in user mode to be used by each process.
.\".It Fl v Ar n
.\"Impose a limit of
.\".Ar n
.\"kilobytes on the amount of virtual memory used.
.El
.Pp
As far as
.Ic ulimit
is concerned, a block is 512 bytes.
.Pp
.It Xo
.Ic umask
.Op Fl S
.Op Ar mask
.Xc
Display or set the file permission creation mask, or umask (see
.Xr umask 2 ) .
If the
.Fl S
option is used, the mask displayed or set is symbolic; otherwise, it is an
octal number.
.Pp
Symbolic masks are like those used by
.Xr chmod 1 .
When used, they describe what permissions may be made available (as opposed to
octal masks in which a set bit means the corresponding bit is to be cleared).
For example,
.Dq ug=rwx,o=
sets the mask so files will not be readable, writable, or executable by
.Dq others ,
and is equivalent (on most systems) to the octal mask
.Dq 007 .
.Pp
.It Xo
.Ic unalias
.Op Fl adt
.Op Ar name ...
.Xc
The aliases for the given names are removed.
If the
.Fl a
option is used, all aliases are removed.
If the
.Fl t
or
.Fl d
options are used, the indicated operations are carried out on tracked or
directory aliases, respectively.
.Pp
.It Xo
.Ic unset
.Op Fl fv
.Ar parameter ...
.Xc
Unset the named parameters
.Po
.Fl v ,
the default
.Pc
or functions
.Pq Fl f .
The exit status is non-zero if any of the parameters have the read-only
attribute set, zero otherwise.
.Pp
.It Ic wait Op Ar job ...
Wait for the specified job(s) to finish.
The exit status of
.Ic wait
is that of the last specified job; if the last job is killed by a signal, the
exit status is 128 + the number of the signal (see
.Ic kill -l Ar exit-status
above); if the last specified job can't be found (because it never existed, or
had already finished), the exit status of
.Ic wait
is 127.
See
.Sx Job control
below for the format of
.Ar job .
.Ic wait
will return if a signal for which a trap has been set is received, or if a
.Dv SIGHUP ,
.Dv SIGINT ,
or
.Dv SIGQUIT
signal is received.
.Pp
If no jobs are specified,
.Ic wait
waits for all currently running jobs (if any) to finish and exits with a zero
status.
If job monitoring is enabled, the completion status of jobs is printed
(this is not the case when jobs are explicitly specified).
.Pp
.It Xo
.Ic whence
.Op Fl pv
.Op Ar name ...
.Xc
For each
.Ar name ,
the type of command is listed (reserved word, built-in, alias,
function, tracked alias, or executable).
If the
.Fl p
option is used, a path search is performed even if
.Ar name
is a reserved word, alias, etc.
Without the
.Fl v
option,
.Ic whence
is similar to
.Ic command Fl v
except that
.Ic whence
will find reserved words and won't print aliases as alias commands.
With the
.Fl v
option,
.Ic whence
is the same as
.Ic command Fl V .
Note that for
.Ic whence ,
the
.Fl p
option does not affect the search path used, as it does for
.Ic command .
If the type of one or more of the names could not be determined, the exit
status is non-zero.
.El
.Ss Job control
Job control refers to the shell's ability to monitor and control jobs, which
are processes or groups of processes created for commands or pipelines.
At a minimum, the shell keeps track of the status of the background (i.e.\&
asynchronous) jobs that currently exist; this information can be displayed
using the
.Ic jobs
commands.
If job control is fully enabled (using
.Ic set -m
or
.Ic set -o monitor ) ,
as it is for interactive shells, the processes of a job are placed in their
own process group.
Foreground jobs can be stopped by typing the suspend
character from the terminal (normally ^Z), jobs can be restarted in either the
foreground or background using the
.Ic fg
and
.Ic bg
commands, and the state of the terminal is saved or restored when a foreground
job is stopped or restarted, respectively.
.Pp
Note that only commands that create processes (e.g. asynchronous commands,
subshell commands, and non-built-in, non-function commands) can be stopped;
commands like
.Ic read
cannot be.
.Pp
When a job is created, it is assigned a job number.
For interactive shells, this number is printed inside
.Dq [..] ,
followed by the process IDs of the processes in the job when an asynchronous
command is run.
A job may be referred to in the
.Ic bg ,
.Ic fg ,
.Ic jobs ,
.Ic kill ,
and
.Ic wait
commands either by the process ID of the last process in the command pipeline
(as stored in the
.Ic $!\&
parameter) or by prefixing the job number with a percent
sign
.Pq Sq % .
Other percent sequences can also be used to refer to jobs:
.Bl -tag -width "%+ | %% | %XX"
.It %+ \*(Ba %% \*(Ba %
The most recently stopped job, or, if there are no stopped jobs, the oldest
running job.
.It %-
The job that would be the
.Ic %+
job if the latter did not exist.
.It % Ns Ar n
The job with job number
.Ar n .
.It %? Ns Ar string
The job with its command containing the string
.Ar string
(an error occurs if multiple jobs are matched).
.It % Ns Ar string
The job with its command starting with the string
.Ar string
(an error occurs if multiple jobs are matched).
.El
.Pp
When a job changes state (e.g. a background job finishes or foreground job is
stopped), the shell prints the following status information:
.Pp
.D1 [ Ns Ar number ] Ar flag status command
.Pp
where...
.Bl -tag -width "command"
.It Ar number
is the job number of the job;
.It Ar flag
is the
.Ql +
or
.Ql -
character if the job is the
.Ic %+
or
.Ic %-
job, respectively, or space if it is neither;
.It Ar status
indicates the current state of the job and can be:
.Bl -tag -width "RunningXX"
.It Done Op Ar number
The job exited.
.Ar number
is the exit status of the job, which is omitted if the status is zero.
.It Running
The job has neither stopped nor exited (note that running does not necessarily
mean consuming CPU time \-
the process could be blocked waiting for some event).
.It Stopped Op Ar signal
The job was stopped by the indicated
.Ar signal
(if no signal is given, the job was stopped by
.Dv SIGTSTP ) .
.It Ar signal-description Op Dq core dumped
The job was killed by a signal (e.g. memory fault, hangup); use
.Ic kill -l
for a list of signal descriptions.
The
.Dq core dumped
message indicates the process created a core file.
.El
.It Ar command
is the command that created the process.
If there are multiple processes in
the job, each process will have a line showing its
.Ar command
and possibly its
.Ar status ,
if it is different from the status of the previous process.
.El
.Pp
When an attempt is made to exit the shell while there are jobs in the stopped
state, the shell warns the user that there are stopped jobs and does not exit.
If another attempt is immediately made to exit the shell, the stopped jobs are
sent a
.Dv SIGHUP
signal and the shell exits.
Similarly, if the
.Ic nohup
option is not set and there are running jobs when an attempt is made to exit
a login shell, the shell warns the user and does not exit.
If another attempt
is immediately made to exit the shell, the running jobs are sent a
.Dv SIGHUP
signal and the shell exits.
.Sh FILES
.Bl -tag -width "/etc/suid_profileXX" -compact
.It Pa ~/.profile
User's login profile.
.It Pa /etc/profile
System login profile.
.It Pa /etc/suid_profile
Privileged shell profile.
.It Pa /etc/shells
Shell database.
.El
.Sh SEE ALSO
.Xr csh 1 ,
.Xr ed 1 ,
.Xr ksh 1 ,
.Xr mg 1 ,
.Xr stty 1 ,
.Xr vi 1 ,
.Xr shells 5 ,
.Xr environ 7 ,
.Xr script 7
.Rs
.%A Morris Bolsky
.%A David Korn
.%B The KornShell Command and Programming Language, 2nd Edition
.%D 1995
.%I Prentice Hall
.%O ISBN 0131827006
.Re
.Rs
.%A Stephen G. Kochan
.%A Patrick H. Wood
.%B UNIX Shell Programming, 3rd Edition
.%D 2003
.%I Sams
.%O ISBN 0672324903
.Re
.Rs
.%A IEEE Inc.
.%D 1993
.%O ISBN 1-55937-266-9
.%T IEEE Standard for Information Technology \- Portable Operating \
    System Interface (POSIX) \- Part 2: Shell and Utilities
.Re
.Sh NOTES
.Nm
is implemented as a run-time option of
.Nm pdksh ,
with only those
.Nm
features whose syntax or semantics are incompatible with a traditional Bourne
shell disabled.
Since this leaves some
.Nm
extensions exposed, caution should be used where backwards compatibility with
traditional Bourne or POSIX compliant shells is an issue.
.Sh AUTHORS
.An -nosplit
This shell is based on the public domain 7th edition Bourne shell clone by
.An Charles Forsyth
and parts of the BRL shell by
.An Doug A. Gwyn ,
.An Doug Kingston ,
.An Ron Natalie ,
.An Arnold Robbins ,
.An Lou Salkind ,
and others.
The first release of
.Nm pdksh
was created by
.An Eric Gisin ,
and it was subsequently maintained by
.An John R. MacMillan Aq Mt change!john@sq.sq.com ,
.An Simon J. Gerraty Aq Mt sjg@zen.void.oz.au ,
and
.An Michael Rendell Aq Mt michael@cs.mun.ca .
The
.Pa CONTRIBUTORS
file in the source distribution contains a more complete list of people and
their part in the shell's development.
.\" .Sh BUGS
.\" Any bugs in
.\" .Nm pdksh
.\" should be reported to pdksh@cs.mun.ca.
.\" Please include the version of
.\" .Nm pdksh
.\" .Po
.\" .Ic echo $KSH_VERSION
.\" shows it
.\" .Pc ,
.\" the machine, operating system, and compiler you are using and a description of
.\" how to repeat the bug (a small shell script that demonstrates the bug is best).
.\" The following, if relevant (if you are not sure, include them), can also be
.\" helpful: options you are using (both
.\" .Pa options.h
.\" and
.\" .Ic set Fl o Ic options )
.\" and a copy of your
.\" .Pa config.h
.\" (the file generated by the
.\" .Pa configure
.\" script).
.\" New versions of
.\" .Nm pdksh
.\" can be obtained from ftp://ftp.cs.mun.ca/pub/pdksh.
.\" .Pp
.\" BTW, the most frequently reported bug is:
.\" .Bd -literal -offset indent
.\" $ echo hi | read a; echo $a   # Does not print hi
.\" .Ed
.\" .Pp
.\" I'm aware of this and there is no need to report it.