ksh(1)ksh(1)Name
ksh, rksh - KornShell, a standard/restricted command and programming
language
Syntaxksh [ ±aefhikmnoprstuvx ] [ ±o option ] ... [ -c string ] [ arg ... ]
rksh [ ±aefhikmnoprstuvx ] [ ±o option ] ... [ -c string ] [ arg ... ]
Description
The shell is a command and programming language that executes commands
read from a terminal or a file. The rksh shell is a restricted version
of the command interpreter ksh; it is used to set up login names and
execution environments whose capabilities are more controlled than
those of the standard shell. See Invocation for the meaning of argu‐
ments to the shell.
Definitions
A metacharacter is one of the following characters:
; & ( ) ⎪ < > new-line space tab
A blank is a tab or a space. An identifier is a sequence of letters,
digits, or underscores starting with a letter or underscore. Identi‐
fiers are used as names for functions and `named parameters'. A word
is a sequence of characters separated by one or more non-quoted
metacharacters.
A command is a sequence of characters in the syntax of the shell lan‐
guage. The shell reads each command and carries out the desired action
either directly or by invoking separate utilities. A special command
is a command that is carried out by the shell without creating a sepa‐
rate process. Except for documented side effects, most special com‐
mands can be implemented as separate utilities.
Commands
A simple-command is a sequence of blank separated words which may be
preceded by a parameter assignment list. See Environment below. The
first word specifies the name of the command to be executed. Except as
specified below, the remaining words are passed as arguments to the
invoked command. The command name is passed as argument 0 (see The
value of a simple-command is its exit status if it terminates normally,
or (octal) 200+status if it terminates abnormally (see for a list of
status values).
A pipeline is a sequence of one or more commands separated by ⎪. The
standard output of each command but the last is connected by a to the
standard input of the next command. Each command is run as a separate
process; the shell waits for the last command to terminate. The exit
status of a pipeline is the exit status of the last command.
A list is a sequence of one or more pipelines separated by ;, &, &&, or
⎪⎪, and optionally terminated by ;, &, or ⎪&. Of these five symbols,
;, &, and ⎪& have equal precedence, which is lower than that of && and
⎪⎪. The symbols && and ⎪⎪ also have equal precedence. A semicolon (;)
causes sequential execution of the preceding pipeline; an ampersand (&)
causes asynchronous execution of the preceding pipeline (that is, the
shell does not wait for that pipeline to finish). The symbol ⎪& causes
asynchronous execution of the preceding command or pipeline with a two-
way pipe established to the parent shell. The standard input and out‐
put of the spawned command can be written to and read from by the par‐
ent Shell using the -p option of the special commands read and print
described later. The symbol && (⎪⎪) causes the list following it to be
executed only if the preceding pipeline returns a zero (non-zero)
value. An arbitrary number of new-lines may appear in a list, instead
of a semicolon, to delimit a command.
A command is either a simple-command or one of the following. Unless
otherwise stated, the value returned by a command is that of the last
simple-command executed in the command.
for identifier [ in word ... ] ;do list ;done
Each time a for command is executed, identifier is set to the
next word taken from the in word list. If in word ... is omit‐
ted, then the for command executes the do list once for each
positional parameter that is set (see Parameter Substitution ).
Execution ends when there are no more words in the list.
select identifier [ in word ... ] ;do list ;done
A select command prints on standard error (file descriptor 2),
the set of words, each preceded by a number. If in word ... is
omitted, then the positional parameters are used instead (see
Parameter Substitution below). The PS3 prompt is printed and a
line is read from the standard input. If this line consists of
the number of one of the listed words, then the value of the
parameter identifier is set to the word corresponding to this
number. If this line is empty the selection list is printed
again. Otherwise the value of the parameter identifier is set
to null. The contents of the line read from standard input is
saved in the parameter REPLY. The list is executed for each
selection until a break or end-of-file is encountered.
case word in [ [(]pattern [ ⎪ pattern ] ... ) list ;; ] ... esac
A case command executes the list associated with the first pat‐
tern that matches word. The form of the patterns is the same as
that used for file-name generation (see File Name Generation
below).
if list ;then list [ elif list ;then list ] ... [ ;else list ] ;fi
The list following if is executed and, if it returns a zero exit
status, the list following the first then is executed. Other‐
wise, the list following elif is executed and, if its value is
zero, the list following the next then is executed. Failing
that, the else list is executed. If no else list or then list
is executed, then the if command returns a zero exit status.
while list ;do list ;done
until list ;do list ;done
A while command repeatedly executes the while list and, if the
exit status of the last command in the list is zero, executes
the do list; otherwise the loop terminates. If no commands in
the do list are executed, then the while command returns a zero
exit status; until may be used in place of while to negate the
loop termination test.
(list) Execute list in a separate environment. Note, that if two adja‐
cent open parentheses are needed for nesting, a space must be
inserted to avoid arithmetic evaluation as described below.
{ list;}
The list is simply executed. Note that unlike the metacharac‐
ters ( and ),
{ and } are `reserved words' and must at the beginning of a line
or after a ; in order to be recognized.
[[expression]]
Evaluates expression and returns a zero exit status when expres‐
sion is true. See Conditional Expressions for a description of
expression.
function identifier { list ;}
identifier () { list ;}
Define a function which is referenced by identifier. The body
of the function is the list of commands between { and }. (See
Functions below).
time pipeline
The pipeline is executed and the elapsed time as well as the
user and system time are printed on standard error.
The following reserved words are only recognized as the first word of a
command and when not quoted:
if then else elif fi case esac for while until do done { } function
select time [[ ]] if then else elif fi case esac for
while until do done { } function select time [[ ]]
Comments
A word beginning with # causes that word and all the following charac‐
ters up to a new-line to be ignored.
Aliasing
The first word of each command is replaced by the text of an alias if
an alias for this word has been defined. The first character of an
alias name can be any non-special printable character, but the rest of
the characters must be the same as for a valid identifier. The
replacement string can contain any valid Shell script including the
metacharacters listed above. The first word of each command in the
replaced text, other than any that are in the process of being
replaced, will be tested for aliases. If the last character of the
alias value is a blank then the word following the alias will also be
checked for alias substitution. Aliases can be used to redefine spe‐
cial builtin commands but cannot be used to redefine the reserved words
listed above. Aliases can be created, listed, and exported with the
command and can be removed with the command. Exported aliases remain
in effect for scripts invoked by name, but must be reinitialized for
separate invocations of the Shell (See Invocation below).
Aliasing is performed when scripts are read, not while they are exe‐
cuted. Therefore, for an alias to take effect the alias definition
command has to be executed before the command which references the
alias is read.
Aliases are frequently used as a short hand for full path names. An
option to the aliasing facility allows the value of the alias to be
automatically set to the full pathname of the corresponding command.
These aliases are called tracked aliases. The value of a tracked alias
is defined the first time the corresponding command is looked up and
becomes undefined each time the PATH variable is reset. These aliases
remain tracked so that the next subsequent reference will redefine the
value. Several tracked aliases are compiled into the shell. The -h
option of the command makes each referenced command name into a tracked
alias.
The following `exported aliases' are compiled into the shell but can be
unset or redefined:
autoload=′typeset -fu′
false=′let 0′
functions=′typeset -f′
hash=′alias -t′
history=′fc -l′
integer=′typeset -i′
nohup=′nohup ′
r=′fc -e -′
true=′:′
type=′whence -v′
Tilde Substitution
After alias substitution is performed, each word is checked to see if
it begins with an unquoted ∼. If it does, then the word up to a / is
checked to see if it matches a user name in the file. If a match is
found, the ∼ and the matched login name is replaced by the login direc‐
tory of the matched user. This is called a `tilde substitution'. If
no match is found, the original text is left unchanged. A ∼ by itself,
or in front of a /, is replaced by the value of the HOME parameter. A
∼ followed by a + or - is replaced by $PWD and $OLDPWD respectively.
In addition, tilde substitution is attempted when the value of a `vari‐
able assignment parameter' begins with a ∼.
Command Substitution
The standard output from a command enclosed in parentheses preceded by
a dollar sign ( $() ) or a pair of grave accents may be used as part or
all of a word; trailing new-lines are removed. In the second (archaic)
form, the string between the quotes is processed for special quoting
characters before the command is executed. (See Quoting). The command
substitution $(cat file) can be replaced by the equivalent but faster
$(<file). Command substitution of most special commands that do not
perform input/output redirection are carried out without creating a
separate process.
An arithmetic expression enclosed in double parenthesis preceded by a
dollar sign ( $(()) ) is replaced by the value of the arithmetic
expression within the double parenthesis.
Process Substitution.
This feature is only available on versions of the operating system that
support the directory for naming open files. Each command argument of
the form <(list) or >(list) will run process list asynchronously con‐
nected to some file in The name of this file will become the argument
to the command. If the form with > is selected then writing on this
file will provide input for list. If < is used, then the file passed
as an argument will contain the output of the list process. For exam‐
ple,
paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1)
>(process2)
cuts fields 1 and 3 from the files file1 and file2 respectively, pastes
the results together, and sends it to the processes process1 and
process2, as well as putting it onto the standard output. Note that
the file, which is passed as an argument to the command, is a system so
programs that expect to on the file will not work.
Parameter Substitution
A parameter is an identifier, one or more digits, or any of the charac‐
ters ∗, @, #, ?, -, $, and !. A `named parameter' (a parameter denoted
by an identifier) has a value and zero or more attributes. Named
parameters can be assigned values and attributes by using the special
command. The attributes supported by the Shell are described later
with the special command. Exported parameters pass values and
attributes to the environment.
The shell supports a one-dimensional array facility. An element of an
array parameter is referenced by a subscript. A subscript is denoted
by a [, followed by an `arithmetic expression' (see Arithmetic Evalua‐
tion) followed by a ]. To assign values to an array, use set -A name
value ... . The value of all subscripts must be in the range of 0
through 1023. Arrays need not be declared. Any reference to a named
parameter with a valid subscript is legal and an array will be created
if necessary. Referencing an array without a subscript is equivalent
to referencing the element zero.
The value of a named parameter may also be assigned by writing:
name=value [ name=value ] ...
If the integer attribute, -i, is set for name the value is subject to
arithmetic evaluation as described below.
Positional parameters, parameters denoted by a number, may be assigned
values with the special command. Parameter $0 is set from argument
zero when the shell is invoked.
The character $ is used to introduce substitutable parameters.
${parameter} The shell reads all the characters from ${ to
the matching } as part of the same word even if
it contains braces or metacharacters. The
value, if any, of the parameter is substituted.
The braces are required when parameter is fol‐
lowed by a letter, digit, or underscore that is
not to be interpreted as part of its name or
when a named parameter is subscripted. If
parameter is one or more digits then it is a
positional parameter. A positional parameter
of more than one digit must be enclosed in
braces. If parameter is ∗ or @, then all the
positional parameters, starting with $1, are
substituted (separated by a field separator
character). If an array identifier with sub‐
script ∗ or @ is used, then the value for each
of the elements is substituted (separated by a
field separator character).
${#parameter} If parameter is ∗ or @, the number of posi‐
tional parameters is substituted. Otherwise,
the length of the value of the parameter is
substituted.
${#identifier[*]} The number of elements in the array identifier
is substituted.
${parameter:-word} If parameter is set and is non-null then sub‐
stitute its value; otherwise substitute word.
${parameter:=word} If parameter is not set or is null then set it
to word; the value of the parameter is then
substituted. Positional parameters may not be
assigned to in this way.
${parameter:?word} If parameter is set and is non-null then sub‐
stitute its value; otherwise, print word and
exit from the shell. If word is omitted then a
standard message is printed.
${parameter:+word} If parameter is set and is non-null then sub‐
stitute word; otherwise substitute nothing.
${parameter#pattern}
${parameter##pattern} If the Shell pattern matches the beginning of
the value of parameter, then the value of this
substitution is the value of the parameter with
the matched portion deleted; otherwise the
value of this parameter is substituted. In the
first form the smallest matching pattern is
deleted and in the second form the largest
matching pattern is deleted.
${parameter%pattern}
${parameter%%pattern} If the Shell pattern matches the end of the
value of parameter, then the value of this sub‐
stitution is the value of the parameter with
the matched part deleted; otherwise substitute
the value of parameter. In the first form the
smallest matching pattern is deleted and in the
second form the largest matching pattern is
deleted.
In the above, word is not evaluated unless it is to be used as the sub‐
stituted string, so that, in the following example, is executed only if
d is not set or is null:
echo ${d:-$(pwd)}
If the colon ( : ) is omitted from the above expressions, then the
shell only checks whether parameter is set or not.
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
- Flags supplied to the shell on invocation or by the com‐
mand.
? The decimal value returned by the last executed command.
$ The process number of this shell.
_ Initially, the value _ is an absolute pathname of the
shell or script being executed as passed in the environ‐
ment. Subsequently it is assigned the last argument of
the previous command. This parameter is not set for
commands which are asynchronous. file when checking for
mail.
! The process number of the last background command
invoked.
ERRNO The value of errno as set by the most recently failed
system call. This value is system dependent and is
intended for debugging purposes.
LINENO The line number of the current line within the script or
function being executed.
OLDPWD The previous working directory set by the command.
OPTARG The value of the last option argument processed by the
special command.
OPTIND The index of the last option argument processed by the
special command.
PPID The process number of the parent of the shell.
PWD The present working directory set by the command.
RANDOM Each time this parameter is referenced, a random inte‐
ger, uniformly distributed between 0 and 32767, is gen‐
erated. The sequence of random numbers can be initial‐
ized by assigning a numeric value to RANDOM.
REPLY This parameter is set by the select statement and by the
read special command when no arguments are supplied.
SECONDS Each time this parameter is referenced, the number of
seconds since shell invocation is returned. If this
parameter is assigned a value, then the value returned
upon reference will be the value that was assigned plus
the number of seconds since the assignment.
The following parameters are used by the shell:
CDPATH The search path for the command.
COLUMNS If this variable is set, the value is used to define the
width of the edit window for the shell edit modes and
for printing select lists.
EDITOR If the value of this variable ends in emacs, gmacs, or
vi and the VISUAL variable is not set, then the corre‐
sponding option (see Special Command set below) will be
turned on.
ENV If this parameter is set, then parameter substitution is
performed on the value to generate the pathname of the
script that will be executed when the shell is invoked.
(See Invocation below.) This file is typically used for
alias and function definitions.
FCEDIT The default editor name for the fc command.
FPATH The search path for function definitions. This path is
searched when a function with the -u attribute is refer‐
enced and when a command is not found. If an executable
file is found, then it is read and executed in the cur‐
rent environment.
IFS Internal field separators, normally space, tab, and new-
line that is used to separate command words which result
from command or parameter substitution and for separat‐
ing words with the special command read. The first
character of the IFS parameter is used to separate argu‐
ments for the $∗ substitution (See Quoting below).
HISTFILE If this parameter is set when the shell is invoked, then
the value is the pathname of the file that will be used
to store the command history. (See Command re-entry
below.)
HISTSIZE If this parameter is set when the shell is invoked, then
the number of previously entered commands that are
accessible by this shell will be greater than or equal
to this number. The default is 128.
HOME The default argument (home directory) for the cd com‐
mand.
LINES If this variable is set, the value is used to determine
the column length for printing select lists. Select
lists will print vertically until about two-thirds of
LINES lines are filled.
LOGNAME The name of the user's login account, corresponding to
the login name in the user database.
MAIL If this parameter is set to the name of a mail file and
the MAILPATH parameter is not set, then the shell
informs the user of arrival of mail in the specified
file.
MAILCHECK This variable specifies how often (in seconds) the shell
will check for changes in the modification time of any
of the files specified by the MAILPATH or MAIL parame‐
ters. The default value is 600 seconds. When the time
has elapsed the shell will check before issuing the next
prompt.
MAILPATH A colon ( : ) separated list of file names. If this
parameter is set then the shell informs the user of any
modifications to the specified files that have occurred
within the last MAILCHECK seconds. Each file name can
be followed by a ? and a message that will be printed.
The message will undergo parameter substitution with the
parameter, $_ defined as the name of the file that has
changed. The default message is you have mail in $_.
PATH The search path for commands (see Execution below). The
user may not change PATH if executing under (except in
.profile ).
PS1 The value of this parameter is expanded for parameter
substitution to define the primary prompt string which
by default is ``$ ''. The character ! in the primary
prompt string is replaced by the command number (see
Command Re-entry below).
PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop, by
default ``#? ''.
PS4 The value of this parameter is expanded for parameter
substitution and precedes each line of an execution
trace. If omitted, the execution trace prompt is ``+
''.
SHELL The pathname of the shell is kept in the environment.
At invocation, if the basename of this variable matches
the pattern *r*sh, then the shell becomes restricted.
TMOUT If set to a value greater than zero, the shell will ter‐
minate if a command is not entered within the prescribed
number of seconds after issuing the PS1 prompt. (Note
that the shell can be compiled with a maximum bound for
this value which cannot be exceeded.)
VISUAL If the value of this variable ends in emacs, gmacs, or
vi then the corresponding option (see Special Command
set below) will be turned on.
The shell gives default values to PATH, PS1, PS2, MAILCHECK, TMOUT and
IFS, while HOME , SHELL , ENV and MAIL are not set at all by the shell
(although HOME is set by login(1)). On some systems MAIL and SHELL are
also set by login(1)).
Blank Interpretation.
After parameter and command substitution, the results of substitutions
are scanned for the field separator characters ( those found in IFS )
and split into distinct arguments where such characters are found.
Explicit null arguments ("" or (fm(fm) are retained. Implicit null
arguments (those resulting from parameters that have no values) are
removed.
File Name Generation.
Following substitution, each command word is scanned for the characters
∗, ?, and [ unless the -f option has been set. If one of these charac‐
ters appears then the word is regarded as a pattern. The word is
replaced with lexicographically sorted file names that match the pat‐
tern. If no file name is found that matches the pattern, then the word
is left unchanged. When a pattern is used for file name generation,
the character . at the start of a file name or immediately following a
/, as well as the character / itself, must be matched explicitly. In
other instances of pattern matching the / and . are not treated spe‐
cially.
∗ Matches any string, including the null string.
? Matches any single character.
[...] Matches any one of the enclosed characters. A pair of charac‐
ters separated by - matches any character lexically between the
pair, inclusive. If the first character following the opening
"[ " is a "! " then any character not enclosed is matched. A -
can be included in the character set by putting it as the first
or last character. A pattern-list is a list of one or more pat‐
terns separated by each other with a ⎪. Composite patterns can
be formed with one or more of the following:
?(pattern-list)
Optionally matches any one of the given patterns.
*(pattern-list)
Matches zero or more occurrences of the given patterns.
+(pattern-list)
Matches one or more occurrences of the given patterns.
@(pattern-list)
Matches exactly one of the given patterns.
!(pattern-list)
Matches anything, except one of the given patterns.
Quoting.
Each of the metacharacters listed above (See Definitions above) has a
special meaning to the shell and causes termination of a word unless
quoted. A character may be quoted (that is, made to stand for itself)
by preceding it with a \. The pair \new-line is ignored. All charac‐
ters enclosed between a pair of single quote marks (′′), are quoted. A
single quote cannot appear within single quotes. Inside double quote
marks (""), parameter and command substitution occurs and \ quotes the
characters \, `, ", and $. The meaning of $∗ and $@ is identical when
not quoted or when used as a parameter assignment value or as a file
name. However, when used as a command argument, $∗ is equivalent to
"$1d$2d...", where d is the first character of the IFS parameter,
whereas $@ is equivalent to $1 "$2" .... Inside grave quote marks \
quotes the characters \, and
If the grave quotes occur within double quotes then \ also quotes the
character ".
The special meaning of reserved words or aliases can be removed by
quoting any character of the reserved word. The recognition of func‐
tion names or special command names listed below cannot be altered by
quoting them.
Arithmetic Evaluation.
An ability to perform integer arithmetic is provided with the special
command let. Evaluations are performed using long arithmetic. Con‐
stants are of the form [base#]n where base is a decimal number between
two and thirty-six representing the arithmetic base and n is a number
in that base. If base is omitted then base 10 is used.
An arithmetic expression uses the same syntax, precedence, and associa‐
tivity of expression of the C language. All the integral operators,
other than ++, --, ?:, and , are supported. Named parameters can be
referenced by name within an arithmetic expression without using the
parameter substitution syntax. When a named parameter is referenced,
its value is evaluated as an arithmetic expression.
An internal integer representation of a named parameter can be speci‐
fied with the -i option of the typeset special command. Arithmetic
evaluation is performed on the value of each assignment to a named
parameter with the -i attribute. If you do not specify an arithmetic
base, the first assignment to the parameter determines the arithmetic
base. This base is used when parameter substitution occurs.
Since many of the arithmetic operators require quoting, an alternative
form of the let command is provided. For any command which begins with
a ((, all the characters until a matching )) are treated as a quoted
expression. More precisely, ((...)) is equivalent to let "...".
Prompting.
When used interactively, the shell prompts with the value of PS1 before
reading a command. If at any time a new-line is typed and further
input is needed to complete a command, then the secondary prompt (that
is, the value of PS2) is issued.
Conditional Expressions.
A conditional expression is used with the [[ compound command to test
attributes of files and to compare strings. Word splitting and file
name generation are not performed on the words between [[ and ]]. Each
expression can be constructed from one or more of the following unary
or binary expressions:
-a file True, if file exists.
-b file True, if file exists and is a block special file.
-c file True, if file exists and is a character special file.
-d file True, if file exists and is a directory.
-f file True, if file exists and is an ordinary file.
-g file True, if file exists and is has its setgid bit set.
-k file True, if file exists and is has its sticky bit set.
-n string True, if length of string is non-zero.
-o option True, if option named option is on.
-p file True, if file exists and is a fifo special file or a
pipe.
-r file True, if file exists and is readable by current
process.
-s file True, if file exists and has size greater than zero.
-t fildes True, if file descriptor number fildes is open and
associated with a terminal device.
-u file True, if file exists and is has its setuid bit set.
-w file True, if file exists and is writable by current
process.
-x file True, if file exists and is executable by current
process. If file exists and is a directory, then the
current process has permission to search in the
directory.
-z string True, if length of string is zero.
-L file True, if file exists and is a symbolic link.
-O file True, if file exists and is owned by the effective
user id of this process.
-G file True, if file exists and its group matches the effec‐
tive group id of this process.
-S file True, if file exists and is a socket.
file1 -nt file2 True, if file1 exists and is newer than file2.
file1 -ot file2 True, if file1 exists and is older than file2.
file1 -ef file2 True, if file1 and file2 exist and refer to the same
file.
string = pattern True, if string matches pattern.
string != pattern True, if string does not match pattern.
string1 < string2 True, if string1 comes before string2 based on ASCII
value of their characters.
string1 > string2 True, if string1 comes after string2 based on ASCII
value of their characters.
exp1 -eq exp2 True, if exp1 is equal to exp2.
exp1 -ne exp2 True, if exp1 is not equal to exp2.
exp1 -lt exp2 True, if exp1 is less than exp2.
exp1 -gt exp2 True, if exp1 is greater than exp2.
exp1 -le exp2 True, if exp1 is less than or equal to exp2.
exp1 -ge exp2 True, if exp1 is greater than or equal to exp2.
In each of the above expressions, if file is of the form /dev/fd/n,
where n is an integer, then the test applied to the open file whose
descriptor number is n.
A compound expression can be constructed from these primitives by using
any of the following, listed in decreasing order of precedence.
(expression) True, if expression is true. Used to group
expressions.
! expression True if expression is false.
expression1 && expression2
True, if expression1 and expression2 are both
true.
expression1 ⎪⎪ expression2
True, if either expression1 or expression2 is
true.
Input/output.
Before a command is executed, its input and output may be redirected
using a special notation interpreted by the shell. The following may
appear anywhere in a simple-command or may precede or follow a command
and are not passed on to the invoked command. Command and parameter
substitution occurs before word or digit is used except as noted below.
File name generation occurs only if the pattern matches a single file
and blank interpretation is not performed.
<word Use file word as standard input (file descriptor 0).
>word Use file word as standard output (file descriptor 1). If
the file does not exist then it is created. If the file
exists, and the noclobber option is on, this causes an
error; otherwise, it is truncated to zero length.
>|word Sames as >, except that it overrides the noclobber
option.
>>word Use file word as standard output. If the file exists
then output is appended to it (by first seeking to the
end-of-file); otherwise, the file is created.
<>word Open file word for reading and writing as standard input.
<<[-]word The shell input is read up to a line that is the same as
word, or to an end-of-file. No parameter substitution,
command substitution or file name generation is performed
on word. The resulting document, called a here-document,
becomes the standard input. If any character of word is
quoted, then no interpretation is placed upon the charac‐
ters of the document; otherwise, parameter and command
substitution occurs, \new-line is ignored, and \ must be
used to quote the characters \, $, and the first charac‐
ter of word. If - is appended to <<, then all leading
tabs are stripped from word and from the document.
<&digit The standard input is duplicated from file descriptor
digit (see dup(2)). Similarly for the standard output
using >& digit.
<&- The standard input is closed. Similarly for the standard
output using >&-.
<&p The input from the co-process is moved to standard input.
>&p The output to the co-process is moved to standard output.
If one of the above is preceded by a digit, then the file descriptor
number referred to is that specified by the digit (instead of the
default 0 or 1). For example:
... 2>&1
means file descriptor 2 is to be opened for writing as a duplicate of
file descriptor 1.
The order in which redirections are specified is significant. The
shell evaluates each redirection in terms of the (file descriptor,
file) association at the time of evaluation. For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then associates
file descriptor 2 with the file associated with file descriptor 1 (that
is, fname). If the order of redirections were reversed, file descrip‐
tor 2 would be associated with the terminal (assuming file descriptor 1
had been) and then file descriptor 1 would be associated with file
fname.
If a command is followed by & and job control is not active, then the
default standard input for the command is the empty file /dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by input/output
specifications.
Environment.
The environment (see environ(7)) is a list of name-value pairs that is
passed to an executed program in the same way as a normal argument
list. The names must be identifiers and the values are character
strings. The shell interacts with the environment in several ways. On
invocation, the shell scans the environment and creates a parameter for
each name found, giving it the corresponding value and marking it
export . Executed commands inherit the environment. If the user modi‐
fies the values of these parameters or creates new ones, using the
export or typeset -x commands they become part of the environment. The
environment seen by any executed command is thus composed of any name-
value pairs originally inherited by the shell, whose values may be mod‐
ified by the current shell, plus any additions which must be noted in
export or typeset -x commands.
The environment for any simple-command or function may be augmented by
prefixing it with one or more parameter assignments. A parameter
assignment argument is a word of the form identifier=value. Thus:
TERM=450 cmd args and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is concerned).
If the -k flag is set, all parameter assignment arguments are placed in
the environment, even if they occur after the command name. The fol‐
lowing first prints a=b c and then c:
echo a=b c
set -k
echo a=b c
This feature is intended for use with scripts written for early ver‐
sions of the shell and its use in new scripts is strongly discouraged.
It is likely to disappear someday.
Functions.
The function reserved word, described in the Commands section above, is
used to define shell functions. Shell functions are read in and stored
internally. Alias names are resolved when the function is read. Func‐
tions are executed like commands with the arguments passed as posi‐
tional parameters. (See Execution below).
Functions execute in the same process as the caller and share all files
and present working directory with the caller. Traps caught by the
caller are reset to their default action inside the function. A trap
condition that is not caught or ignored by the function causes the
function to terminate and the condition to be passed on to the caller.
A trap on EXIT set inside a function is executed after the function
completes in the environment of the caller. Ordinarily, variables are
shared between the calling program and the function. However, the
typeset special command used within a function defines local variables
whose scope includes the current function and all functions it calls.
The special command return is used to return from function calls.
Errors within functions return control to the caller.
Function identifiers can be listed with the -f or +f option of the
typeset special command. The text of functions will also be listed
with -f. Function can be undefined with the -f option of the unset
special command.
Ordinarily, functions are unset when the shell executes a shell script.
The -xf option of the typeset command allows a function to be exported
to scripts that are executed without a separate invocation of the
shell. Functions that need to be defined across separate invocations
of the shell should be specified in the ENV file with the -xf option of
typeset
Jobs.
If the monitor option of the set command is turned on, an interactive
shell associates a job with each pipeline. It keeps a table of current
jobs, printed by the jobs command, and assigns them small integer num‐
bers. When a job is started asynchronously with &, the shell prints a
line which looks like:
[1] 1234
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process id was 1234.
This paragraph and the next require features that are not in all ver‐
sions of the UNIX operating system and may not apply. If you are run‐
ning a job and wish to do something else you may hit the key ^Z (con‐
trol-Z) which sends a STOP signal to the current job. The shell will
then normally indicate that the job has been `Stopped', and print
another prompt. You can then manipulate the state of this job, putting
it in the background with the bg command, or run some other commands
and then eventually bring the job back into the foreground with the
foreground command fg. A ^Z takes effect immediately and is like an
interrupt in that pending output and unread input are discarded when it
is typed.
A job being run in the background will stop if it tries to read from
the terminal. Background jobs are normally allowed to produce output,
but this can be disabled by giving the command ``stty tostop''. If you
set this tty option, then background jobs will stop when they try to
produce output like they do when they try to read input.
There are several ways to refer to jobs in the shell. A job can be
referred to by the process id of any process of the job or by one of
the following:
%number The job with the given number.
%string Any job whose command line begins with string.
%?string Any job whose command line contains string.
%% Current job.
%+ Equivalent to %%.
%- Previous job.
This shell learns immediately whenever a process changes state. It
normally informs you whenever a job becomes blocked so that no further
progress is possible, but only just before it prints a prompt. This is
done so that it does not otherwise disturb your work.
When the monitor mode is on, each background job that completes trig‐
gers any trap set for CHLD.
When you try to leave the shell while jobs are running or stopped, you
will be warned that `You have stopped(running) jobs.' You may use the
jobs command to see what they are. If you do this or immediately try
to exit again, the shell will not warn you a second time, and the
stopped jobs will be terminated.
Signals.
The INT and QUIT signals for an invoked command are ignored if the com‐
mand is followed by & and job monitor option is not active. Otherwise,
signals have the values inherited by the shell from its parent (but see
also the trap command below).
Execution.
Each time a command is executed, the above substitutions are carried
out. If the command name matches one of the Special Commands listed
below, it is executed within the current shell process. Next, the com‐
mand name is checked to see if it matches one of the user defined func‐
tions. If it does, the positional parameters are saved and then reset
to the arguments of the function call. When the function completes or
issues a return, the positional parameter list is restored and any trap
set on EXIT within the function is executed. The value of a function
is the value of the last command executed. A function is also executed
in the current shell process. If a command name is not a special com‐
mand or a user defined function, a process is created and an attempt is
made to execute the command via exec(2).
The shell parameter PATH defines the search path for the directory con‐
taining the command. Alternative directory names are separated by a
colon (:). The default path is /bin:/usr/bin: (specifying /bin,
/usr/bin, and the current directory in that order). The current direc‐
tory can be specified by two or more adjacent colons, or by a colon at
the beginning or end of the path list. If the command name contains a
/ then the search path is not used. Otherwise, each directory in the
path is searched for an executable file. If the file has execute per‐
mission but is not a directory or an a.out file, it is assumed to be a
file containing shell commands. A sub-shell is spawned to read it.
All non-exported aliases, functions, and named parameters are removed
in this case. If the shell command file does not have read permission,
or if the setuid and/or setgid bits are set on the file, then the shell
executes an agent whose job it is to set up the permissions and execute
the shell with the shell command file passed down as an open file. A
parenthesized command is executed in a sub-shell without removing non-
exported quantities.
Command Re-entry.
The text of the last HISTSIZE (default 128) commands entered from a
terminal device is saved in a history file. The file $HOME/.sh_history
is used if the HISTFILE variable is not set or is not writable. A
shell can access the commands of all interactive shells which use the
same named HISTFILE. The special command fc is used to list or edit a
portion of this file. The portion of the file to be edited or listed
can be selected by number or by giving the first character or charac‐
ters of the command. A single command or range of commands can be
specified. If you do not specify an editor program as an argument to
fc then the value of the parameter FCEDIT is used. If FCEDIT is not
defined then /bin/ed is used. The edited command(s) is printed and re-
executed upon leaving the editor. The editor name - is used to skip
the editing phase and to re-execute the command. In this case a sub‐
stitution parameter of the form old=new can be used to modify the com‐
mand before execution. For example, if r is aliased to ′fc -e -′ then
typing `r bad=good c' will re-execute the most recent command which
starts with the letter c, replacing the first occurrence of the string
bad with the string good.
In-line Editing Options
Normally, each command line entered from a terminal device is simply
typed followed by a new-line (`RETURN' or `LINE FEED'). If either the
emacs, gmacs, or vi option is active, the user can edit the command
line. To be in either of these edit modes set the corresponding
option. An editing option is automatically selected each time the VIS‐
UAL or EDITOR variable is assigned a value ending in either of these
option names.
The editing features require that the user's terminal accept `RETURN'
as carriage return without line feed and that a space (` ') must over‐
write the current character on the screen. ADM terminal users should
set the "space - advance" switch to `space'. Hewlett-Packard series
2621 terminal users should set the straps to `bcGHxZ etX'.
The editing modes implement a concept where the user is looking through
a window at the current line. The window width is the value of COLUMNS
if it is defined, otherwise 80. If the line is longer than the window
width minus two, a mark is displayed at the end of the window to notify
the user. As the cursor moves and reaches the window boundaries the
window will be centered about the cursor. The mark is a > (<, *) if
the line extends on the right (left, both) side(s) of the window.
The search commands in each edit mode provide access to the history
file. Only strings are matched, not patterns, although a leading ^ in
the string restricts the match to begin at the first character in the
line.
Emacs Editing Mode
This mode is entered by enabling either the emacs or gmacs option. The
only difference between these two modes is the way they handle ^T. To
edit, the user moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed. All the editing
commands are control characters or escape sequences. The notation for
control characters is caret ( ^ ) followed by the character. For exam‐
ple, ^F is the notation for control F. This is entered by depressing
`f' while holding down the `CTRL' (control) key. The `SHIFT' key is
not depressed. (The notation ^? indicates the DEL (delete) key.)
The notation for escape sequences is M- followed by a character. For
example, M-f (pronounced Meta f) is entered by depressing ESC (ascii
033) followed by `f'. (M-F would be the notation for ESC followed by
`SHIFT' (capital) `F'.)
All edit commands operate from any place on the line (not just at the
beginning). Neither the "RETURN" nor the "LINE FEED" key is entered
after edit commands except when noted.
^F Move cursor forward (right) one character.
M-f Move cursor forward one word. (The emacs editor's idea of a
word is a string of characters consisting of only letters,
digits and underscores.)
^B Move cursor backward (left) one character.
M-b Move cursor backward one word.
^A Move cursor to start of line.
^E Move cursor to end of line.
^]char Move cursor forward to character char on current line.
M-^]char Move cursor back to character char on current line.
^X^X Interchange the cursor and mark.
erase (User defined erase character as defined by the stty(1) com‐
mand, usually ^H or #.) Delete previous character.
^D Delete current character.
M-d Delete current word.
M-^H (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-DEL) Delete previous word (if your interrupt character
is ^? (DEL, the default) then this command will not work).
^T Transpose current character with next character in emacs
mode. Transpose two previous characters in gmacs mode.
^C Capitalize current character.
M-c Capitalize current word.
M-l Change the current word to lower case.
^K Delete from the cursor to the end of the line. If preceded
by a numerical parameter whose value is less than the current
cursor position, then delete from given position up to the
cursor. If preceded by a numerical parameter whose value is
greater than the current cursor position, then delete from
cursor up to given cursor position.
^W Kill from the cursor to the mark.
M-p Push the region from the cursor to the mark on the stack.
kill (User defined kill character as defined by the stty command,
usually ^G or @.) Kill the entire current line. If two kill
characters are entered in succession, all kill characters
from then on cause a line feed (useful when using paper ter‐
minals).
^Y Restore last item removed from line. (Yank item back to the
line.)
^L Line feed and print current line.
^@ (Null character) Set mark.
M-space (Meta space) Set mark.
^J (New line) Execute the current line.
^M (Return) Execute the current line.
eof End-of-file character, normally ^D, is processed as an End-
of-file only if the current line is null.
^P Fetch previous command. Each time ^P is entered the previous
command back in time is accessed. Moves back one line when
not on the first line of a multi-line command.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command line. Each time ^N is entered the next
command line forward in time is accessed.
^Rstring Reverse search history for a previous command line containing
string. If a parameter of zero is given, the search is for‐
ward. String is terminated by a "RETURN" or "NEW LINE". If
string is preceded by a ^, the matched line must begin with
string. If string is omitted, then the next command line
containing the most recent string is accessed. In this case
a parameter of zero reverses the direction of the search.
^O Operate - Execute the current line and fetch the next line
relative to current line from the history file.
M-digits (Escape) Define numeric parameter, the digits are taken as a
parameter to the next command. The commands that accept a
parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-.,
M-^], M-_, M-b, M-c, M-d, M-f, M-h M-l and M-^H.
M-letter Soft-key - Your alias list is searched for an alias by the
name _letter and if an alias of this name is defined, its
value will be inserted on the input queue. The letter must
not be one of the above meta-functions. M-]letter Soft-key -
Your alias list is searched for an alias by the name __letter
and if an alias of this name is defined, its value will be
inserted on the input queue. The can be used to program
functions keys on many terminals.
M-. The last word of the previous command is inserted on the
line. If preceded by a numeric parameter, the value of this
parameter determines which word to insert rather than the
last word.
M-_ Same as M-..
M-* Attempt file name generation on the current word. An aster‐
isk is appended if the word does not match any file or con‐
tain any special pattern characters.
M-ESC File name completion. Replaces the current word with the
longest common prefix of all filenames matching the current
word with an asterisk appended. If the match is unique, a /
is appended if the file is a directory and a space is
appended if the file is not a directory.
M-= List files matching current word pattern if an asterisk were
appended.
^U Multiply parameter of next command by 4.
\ Escape next character. Editing characters, the user's erase,
kill and interrupt (normally ^?) characters may be entered
in a command line or in a search string if preceded by a \.
The \ removes the next character's editing features (if any).
^V Display version of the shell.
M-Inserta at the beginning of the line and execute it. This causes a
comment to be inserted in the history file.
Vi Editing Mode
There are two typing modes. Initially, when you enter a command you
are in the input mode. To edit, the user enters control mode by typing
ESC ( 033 ) and moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed. Most control
commands accept an optional repeat count prior to the command.
When in vi mode on most systems, canonical processing is initially
enabled and the command will be echoed again if the speed is 1200 baud
or greater and it contains any control characters or less than one sec‐
ond has elapsed since the prompt was printed. The ESC character termi‐
nates canonical processing for the remainder of the command and the
user can then modify the command line. This scheme has the advantages
of canonical processing with the type-ahead echoing of raw mode.
If the option viraw is also set, the terminal will always have canoni‐
cal processing disabled. This mode is implicit for systems that do not
support two alternate end of line delimiters, and may be helpful for
certain terminals.
Input Edit Commands
By default the editor is in input mode.
erase (User defined erase character as defined by the stty
command, usually ^H or #.) Delete previous character.
^W Delete the previous blank separated word.
^D Terminate the shell.
^V Escape next character. Editing characters, the user's
erase or kill characters may be entered in a command
line or in a search string if preceded by a ^V. The
^V removes the next character's editing features (if
any).
\ Escape the next erase or kill character.
Motion Edit Commands
These commands will move the cursor.
[count]l Cursor forward (right) one character.
[count]w Cursor forward one alpha-numeric word.
[count]W Cursor to the beginning of the next word that follows
a blank.
[count]e Cursor to end of word.
[count]E Cursor to end of the current blank delimited word.
[count]h Cursor backward (left) one character.
[count]b Cursor backward one word.
[count]B Cursor to preceding blank separated word.
[count]⎪ Cursor to column count.
[count]fc Find the next character c in the current line.
[count]Fc Find the previous character c in the current line.
[count]tc Equivalent to f followed by h.
[count]Tc Equivalent to F followed by l.
[count]; Repeats count times, the last single character find
command, f, F, t, or T.
[count], Reverses the last single character find command count
times.
0 Cursor to start of line.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is entered the
previous command back in time is accessed.
[count]- Equivalent to k.
[count]j Fetch next command. Each time j is entered the next
command forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The default is
the least recent history command.
/string Search backward through history for a previous command
containing string. String is terminated by a "RETURN"
or "NEW LINE". If string is preceded by a ^, the
matched line must begin with string. If string is
null the previous string will be used.
?string Same as / except that search will be in the forward
direction.
n Search for next match of the last pattern to / or ?
commands.
N Search for next match of the last pattern to / or ?,
but in reverse direction. Search history for the
string entered by the previous / command.
Text Modification Edit Commands
These commands will modify the line.
a Enter input mode and enter text after the current
character.
A Append text to the end of the line. Equivalent to $a.
[count]cmotion
c[count]motion
Delete current character through the character that
motion would move the cursor to and enter input mode.
If motion is c, the entire line will be deleted and
input mode entered.
C Delete the current character through the end of line
and enter input mode. Equivalent to c$.
S Equivalent to cc.
D Delete the current character through the end of line.
Equivalent to d$.
[count]dmotion
d[count]motion
Delete current character through the character that
motion would move to. If motion is d , the entire
line will be deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line. Equiva‐
lent to 0i.
[count]P Place the previous text modification before the cur‐
sor.
[count]p Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen
with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the current
cursor position with c, and advance the cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]∼ Invert the case of the count character(s) starting at
the current cursor position and advance the cursor.
[count]_ Causes the count word of the previous command to be
appended and input mode entered. The last word is
used if count is omitted.
* Causes an * to be appended to the current word and
file name generation attempted. If no match is found,
it rings the bell. Otherwise, the word is replaced by
the matching pattern and input mode is entered.
\ Filename completion. Replaces the current word with
the longest common prefix of all filenames matching
the current word with an asterisk appended. If the
match is unique, a / is appended if the file is a
directory and a space is appended if the file is not a
directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that motion
would move the cursor to and puts them into the delete
buffer. The text and cursor are unchanged.
Y Yanks from current position to end of line. Equiva‐
lent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on the
line.
[count]v Returns the command fc -e ${VISUAL:-${EDITOR:-vi}}
count in the input buffer. If count is omitted, then
the current line is used.
^L Line feed and print current line. Has effect only in
control mode.
^J (New line) Execute the current line, regardless of
mode.
^M (Return) Execute the current line, regardless of mode.
Sends the line after
inserting a in front of the line. Useful for causing
the current line to be inserted in the history without
being executed.
= List the file names that match the current word if an
asterisk were appended it.
@letter Your alias list is searched for an alias by the name
_letter and if an alias of this name is defined, its
value will be inserted on the input queue for process‐
ing.
Special Commands.
The following simple-commands are executed in the shell process.
Input/Output redirection is permitted. Unless otherwise indicated, the
output is written on file descriptor 1 and the exit status, when there
is no syntax error, is zero. Commands that are preceded by one or two
† are treated specially in the following ways:
1. Parameter assignment lists preceding the command remain in
effect when the command completes.
2. I/O redirections are processed after parameter assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by †† that are in the format
of a parameter assignment, are expanded with the same rules as a
parameter assignment. This means that tilde substitution is
performed after the = sign and word splitting and file name gen‐
eration are not performed.
† : [ arg ... ]
The command only expands parameters.
† . file [ arg ... ]
Read the complete file then execute the commands. The commands
are executed in the current Shell environment. The search path
specified by PATH is used to find the directory containing file.
If any arguments arg are given, they become the positional
parameters. Otherwise the positional parameters are unchanged.
The exit status is the exit status of the last command executed.
†† alias [ -tx ] [ name[ =value ] ] ...
Alias with no arguments prints the list of aliases in the form
name=value on standard output. An alias is defined for each
name whose value is given. A trailing space in value causes the
next word to be checked for alias substitution. The -t flag is
used to set and list tracked aliases. The value of a tracked
alias is the full pathname corresponding to the given name. The
value becomes undefined when the value of PATH is reset but the
aliases remained tracked. Without the -t flag, for each name in
the argument list for which no value is given, the name and
value of the alias is printed. The -x flag is used to set or
print exported aliases. An exported alias is defined for
scripts invoked by name. The exit status is non-zero if a name
is given, but no value, for which no alias has been defined.
bg [ job... ]
This command is only on systems that support job control. Puts
each specified job into the background. The current job is put
in the background if job is not specified. See Jobs for a
description of the format of job.
† break [ n ]
Exit from the enclosing for while until or select loop, if any.
If n is specified then break n levels.
† continue [ n ]
Resume the next iteration of the enclosing for while until or
select loop. If n is specified then resume at the n-th enclos‐
ing loop.
cd [ arg ]
cd old new
This command can be in either of two forms. In the first form
it changes the current directory to arg. If arg is - the direc‐
tory is changed to the previous directory. The shell parameter
HOME is the default arg. The parameter PWD is set to the cur‐
rent directory. The shell parameter CDPATH defines the search
path for the directory containing arg. Alternative directory
names are separated by a colon (:). The default path is <null>
(specifying the current directory). Note that the current
directory is specified by a null path name, which can appear
immediately after the equal sign or between the colon delimiters
anywhere else in the path list. If arg begins with a / then the
search path is not used. Otherwise, each directory in the path
is searched for arg.
The second form of cd substitutes the string new for the string
old in the current directory name, PWD and tries to change to
this new directory.
The cd command may not be executed by
echo [ arg ... ]
See echo(1) for usage and description.
† eval [ arg ... ]
The arguments are read as input to the shell and the resulting
command(s) executed.
† exec [ arg ... ]
If arg is given, the command specified by the arguments is exe‐
cuted in place of this shell without creating a new process.
Input/output arguments may appear and affect the current
process. If no arguments are given the effect of this command
is to modify file descriptors as prescribed by the input/output
redirection list. In this case, any file descriptor numbers
greater than 2 that are opened with this mechanism are closed
when invoking another program.
† exit [ n ]
Causes the shell to exit with the exit status specified by n.
If n is omitted then the exit status is that of the last command
executed. An end-of-file will also cause the shell to exit
except for a shell which has the ignoreeof option (See set
below) turned on.
†† export [ name[=value] ] ...
The given names are marked for automatic export to the environ‐
ment of subsequently-executed commands.
fc [ -e ename ] [ -nlr ] [ first [ last ] ]
fc -e - [ old=new ] [ command ]
In the first form, a range of commands from first to last is
selected from the last HISTSIZE commands that were typed at the
terminal. The arguments first and last may be specified as a
number or as a string. A string is used to locate the most
recent command starting with the given string. A negative num‐
ber is used as an offset to the current command number. If the
flag -l, is selected, the commands are listed on standard out‐
put. Otherwise, the editor program ename is invoked on a file
containing these keyboard commands. If ename is not supplied,
then the value of the parameter FCEDIT (default /bin/ed) is used
as the editor. When editing is complete, the edited command(s)
is executed. If last is not specified then it will be set to
first. If first is not specified the default is the previous
command for editing and -16 for listing. The flag -r reverses
the order of the commands and the flag -n suppresses command
numbers when listing. In the second form the command is re-exe‐
cuted after the substitution old=new is performed.
fg [ job... ]
This command is only on systems that support job control. Each
job specified is brought to the foreground. Otherwise, the cur‐
rent job is brought into the foreground. See Jobs for a
description of the format of job.
getopts optstring name [ arg ... ]
Checks arg for legal options. If arg is omitted, the positional
parameters are used. An option argument begins with a + or a -.
An option not beginning with + or - or the argument -- ends the
options. optstring contains the letters that getopts recog‐
nizes. If a letter is followed by a :, that option is expected
to have an argument. The options can be separated from the
argument by blanks.
getopts places the next option letter it finds inside variable
name each time it is invoked with a + prepended when arg begins
with a +. The index of the next arg is stored in OPTIND. The
option argument, if any, gets stored in OPTARG.
A leading : in optstring causes getopts to store the letter of
an invalid option in OPTARG, and to set name to ? for an
unknown option and to : when a required option is missing. Oth‐
erwise, getopts prints an error message. The exit status is
non-zero when there are no more options.
jobs [ -lnp ] [ job ... ]
Lists information about each given job; or all active jobs if
job is omitted. The -l flag lists process ids in addition to
the normal information. The -n flag only displays jobs that
have stopped or exited since last notified. The -p flag causes
only the process group to be listed. See Jobs for a description
of the format of job.
kill [ -sig ] job ...
kill -l
Sends either the TERM (terminate) signal or the specified signal
to the specified jobs or processes. Signals are either given by
number or by names (as given in /usr/include/signal.h, stripped
of the prefix ``SIG''). If the signal being sent is TERM (ter‐
minate) or HUP (hangup), then the job or process will be sent a
CONT (continue) signal if it is stopped. The argument job can
the process id of a process that is not a member of one of the
active jobs. See Jobs for a description of the format of job.
In the second form, kill -l, the signal numbers and names are
listed.
let arg ...
Each arg is a separate arithmetic expression to be evaluated.
See Arithmetic Evaluation above, for a description of arithmetic
expression evaluation.
The exit status is 0 if the value of the last expression is non-zero,
and 1 otherwise.
† newgrp [ arg ... ]
Equivalent to exec /bin/newgrp arg ....
print [ -Rnprsu[n ] ] [ arg ... ]
The shell output mechanism. With no flags or with flag - or --
the arguments are printed on standard output as described by
echo(1). In raw mode, -R or -r, the escape conventions of echo
are ignored. The -R option will print all subsequent arguments
and options other than -n. The -p option causes the arguments
to be written onto the pipe of the process spawned with ⎪&
instead of standard output. The -s option causes the arguments
to be written onto the history file instead of standard output.
The -u flag can be used to specify a one digit file descriptor
unit number n on which the output will be placed. The default
is 1. If the flag -n is used, no new-line is added to the out‐
put.
pwd Equivalent to print -r - $PWD
read [ -prsu[ n ] ] [ name?prompt ] [ name ... ]
The shell input mechanism. One line is read and is broken up
into fields using the characters in IFS as separators. In raw
mode, -r, a \ at the end of a line does not signify line contin‐
uation. The first field is assigned to the first name, the sec‐
ond field to the second name, etc., with leftover fields
assigned to the last name. The -p option causes the input line
to be taken from the input pipe of a process spawned by the
shell using ⎪&. If the -s flag is present, the input will be
saved as a command in the history file. The flag -u can be used
to specify a one digit file descriptor unit to read from. The
file descriptor can be opened with the exec special command.
The default value of n is 0. If name is omitted then REPLY is
used as the default name. The exit status is 0 unless an end-
of-file is encountered. An end-of-file with the -p option
causes cleanup for this process so that another can be spawned.
If the first argument contains a ?, the remainder of this word
is used as a prompt on standard error when the shell is interac‐
tive. The exit status is 0 unless an end-of-file is encoun‐
tered.
†† readonly [ name[=value] ] ...
The given names are marked readonly and these names cannot be
changed by subsequent assignment.
† return [ n ]
Causes a shell function to return to the invoking script with
the return status specified by n. If n is omitted then the
return status is that of the last command executed. If return
is invoked while not in a function or a . script, then it is
the same as an exit.
set [ ±aefhkmnopstuvx ] [ ±o option ]... [ ±A name ] [ arg ... ]
The flags for this command have meaning as follows:
-A Array assignment. Unset the variable name and assign
values sequentially from the list arg. If +A is used,
the variable name is not unset first.
-a All subsequent parameters that are defined are automati‐
cally exported.
-e If a command has a non-zero exit status, execute the ERR
trap, if set, and exit. This mode is disabled while
reading profiles.
-f Disables file name generation.
-h Each command becomes a tracked alias when first encoun‐
tered.
-k All parameter assignment arguments are placed in the
environment for a command, not just those that precede
the command name.
-m Background jobs will run in a separate process group and
a line will print upon completion. The exit status of
background jobs is reported in a completion message. On
systems with job control, this flag is turned on auto‐
matically for interactive shells.
-n Read commands and check them for syntax errors, but do
not execute them. Ignored for interactive shells.
-o The following argument can be one of the following
option names:
allexport
Same as -a.
errexit Same as -e.
bgnice All background jobs are run at a lower priority.
This is the default mode.
emacs Puts you in an emacs style in-line editor for
command entry.
gmacs Puts you in a gmacs style in-line editor for
command entry.
ignoreeof
The shell will not exit on end-of-file. The
command exit must be used.
keyword Same as -k.
markdirs
All directory names resulting from file name
generation have a trailing / appended.
monitor Same as -m.
noclobber
Prevents redirection > from truncating existing
files. Require >⎪ to truncate a file when
turned on.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in history
file.
nounset Same as -u.
privileged
Same as -p.
verbose Same as -v.
trackall
Same as -h.
vi Puts you in insert mode of a vi style in-line
editor until you hit escape character 033. This
puts you in move mode. A return sends the line.
viraw Each character is processed as it is typed in vi
mode.
xtrace Same as -x.
If no option name is supplied then the current option
settings are printed.
-p Disables processing of the $HOME/.profile file and uses
the file /etc/suid_profile instead of the ENV file.
This mode is on whenever the effective uid (gid) is not
equal to the real uid (gid). Turning this off causes
the effective uid and gid to be set to the real uid and
gid.
-s Sort the positional parameters lexicographically.
-t Exit after reading and executing one command.
-u Treat unset parameters as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
- Turns off -x and -v flags and stops examining arguments
for flags.
-- Do not change any of the flags; useful in setting $1 to
a value beginning with -. If no arguments follow this
flag then the positional parameters are unset.
Using + rather than - causes these flags to be turned
off. These flags can also be used upon invocation of
the shell. The current set of flags may be found in $-.
Unless -A is specified, the remaining arguments are
positional parameters and are assigned, in order, to $1
$2 .... If no arguments are given then the names and
values of all named parameters are printed on the stan‐
dard output. If the only argument is +, the names of
all named parameters are printed.
† shift [ n ]
The positional parameters from $n+1 ... are renamed $1 ... ,
default n is 1. The parameter n can be any arithmetic expres‐
sion that evaluates to a non-negative number less than or equal
to $#.
† times
Print the accumulated user and system times for the shell and
for processes run from the shell.
† trap [ arg ] [ sig ] ...
arg is a command to be read and executed when the shell receives
signal(s) sig. (Note that arg is scanned once when the trap is
set and once when the trap is taken.) Each sig can be given as
a number or as the name of the signal. Trap commands are exe‐
cuted in order of signal number. Any attempt to set a trap on a
signal that was ignored on entry to the current shell is inef‐
fective. If arg is omitted or is -, then all trap(s) sig are
reset to their original values. If arg is the null string then
this signal is ignored by the shell and by the commands it
invokes. If sig is ERR then arg will be executed whenever a
command has a non-zero exit status. sig is DEBUG then arg will
be executed after each command. If sig is 0 or EXIT and the
trap statement is executed inside the body of a function, then
the command arg is executed after the function completes. If
sig is 0 or EXIT for a trap set outside any function then the
command arg is executed on exit from the shell. The trap com‐
mand with no arguments prints a list of commands associated with
each signal number.
†† typeset [ ±HLRZfilrtux[n] ] [ name[ =value ] ] ...
Sets attributes and values for shell parameters. When invoked
inside a function, a new instance of the parameter name is cre‐
ated. The parameter value and type are restored when the func‐
tion completes. The following list of attributes may be speci‐
fied:
-H This flag provides UNIX system to host-name file mapping
on non-UNIX system machines.
-L Left justify and remove leading blanks from value. If n
is non-zero it defines the width of the field, otherwise
it is determined by the width of the value of first
assignment. When the parameter is assigned to, it is
filled on the right with blanks or truncated, if neces‐
sary, to fit into the field. Leading zeros are removed
if the -Z flag is also set. The -R flag is turned off.
-R Right justify and fill with leading blanks. If n is non-
zero it defines the width of the field, otherwise it is
determined by the width of the value of first assignment.
The field is left filled with blanks or truncated from
the end if the parameter is reassigned. The L flag is
turned off.
-Z Right justify and fill with leading zeros if the first
non-blank character is a digit and the -L flag has not
been set. If n is non-zero it defines the width of the
field, otherwise it is determined by the width of the
value of first assignment.
-f The names refer to function names rather than parameter
names. No assignments can be made and the only other
valid flags are -t, -u and -x. The flag -t turns on exe‐
cution tracing for this function. The flag -u causes
this function to be marked undefined. The FPATH variable
will be searched to find the function definition when the
function is referenced. The flag -x allows the function
definition to remain in effect across shell procedures
invoked by name.
-i Parameter is an integer. This makes arithmetic faster.
If n is non-zero it defines the output arithmetic base,
otherwise the first assignment determines the output
base.
-l All upper-case characters converted to lower-case. The
upper-case flag, -u is turned off.
-r The given names are marked readonly and these names can‐
not be changed by subsequent assignment.
-t Tags the named parameters. Tags are user definable and
have no special meaning to the shell.
-u All lower-case characters are converted to upper-case
characters. The lower-case flag, -l is turned off.
-x The given names are marked for automatic export to the
environment of subsequently-executed commands.
Using + rather than - causes these flags to be turned off. If
no name arguments are given but flags are specified, a list of
names (and optionally the values) of the parameters which have
these flags set is printed. (Using + rather than - keeps the
values from being printed.) If no names and flags are given,
the names and attributes of all parameters are printed.
ulimit [ -HSacdfmnpstvw ] [ limit ]
Set or display a resource limit. The available resources limits
listed below. Many systems to not contain one or more of these
limits. The limit for a specified resource is set when limit is
specified. The value of limit can be a number in the unit spec‐
ified below with each resource, or the value unlimited. The H
and S flags specify whether the hard limit or the soft limit for
the given resource is set. A hard limit cannot be increased
once it is set. A soft limit can be increased up to the value
of the hard limit. If neither the H or S options is specified,
the limit applies to both. The current resource limit is
printed when limit is omitted. In this case the soft limit is
printed unless H is specified. When more that one resource is
specified, then the limit name and unit is printed before the
value.
-a Lists all of the current resource limits.
-c The number of 512-byte blocks on the size of core dumps.
-d The number of K-bytes on the size of the data area.
-f The number of 512-byte blocks on files written by child
processes (files of any size may be read).
-m The number of K-bytes on the size of physical memory.
-n The number of file descriptors.
-p The number of 512-byte blocks for pipe buffering.
-s The number of K-bytes on the size of the stack area.
-t The number of seconds to be used by each process.
-v The number of K-bytes for virtual memory.
-w The number of K-bytes for the swap area.
If no option is given, -f is assumed.
umask [ mask ]
The user file-creation mask is set to mask (see umask(2)). mask
can either be an octal number or a symbolic value as described
in chmod(1). If a symbolic value is given, the new umask value
is the complement of the result of applying mask to the comple‐
ment of the previous umask value. If mask is omitted, the cur‐
rent value of the mask is printed.
unalias name ...
The parameters given by the list of names are removed from the
alias list.
unset [ -f ] name ...
The parameters given by the list of names are unassigned, i. e.,
their values and attributes are erased. Readonly variables can‐
not be unset. If the flag, -f, is set, then the names refer to
function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG,
OPTIND, RANDOM, SECONDS, TMOUT, and _ causes removes their spe‐
cial meaning even if they are subsequently assigned to.
† wait [ job ]
Wait for the specified job and report its termination status.
If job is not given then all currently active child processes
are waited for. The exit status from this command is that of
the process waited for. See Jobs for a description of the for‐
mat of job.
whence [ -pv ] name ...
For each name, indicate how it would be interpreted if used as a
command name.
The flag, -v, produces a more verbose report.
The flag, -p, does a path search for name even if name is an
alias, a function, or a reserved word.
Invocation.
If the shell is invoked by exec(2), and the first character of argument
zero ($0) is -, then the shell is assumed to be a login shell and com‐
mands are read from /etc/profile and then from either .profile in the
current directory or $HOME/.profile, if either file exists. Next, com‐
mands are read from the file named by performing parameter substitution
on the value of the environment parameter ENV if the file exists. If
the -s flag is not present and arg is, then a path search is performed
on the first arg to determine the name of the script to execute. The
script arg must have read permission and any setuid and getgid settings
will be ignored. Commands are then read as described below; the fol‐
lowing flags are interpreted by the shell when it is invoked:
-c string If the -c flag is present then commands are read from string.
-s If the -s flag is present or if no arguments remain then com‐
mands are read from the standard input. Shell output, except
for the output of the Special commands listed above, is writ‐
ten to file descriptor 2.
-i If the -i flag is present or if the shell input and output
are attached to a terminal (as told by ioctl(2)) then this
shell is interactive. In this case TERM is ignored (so that
kill 0 does not kill an interactive shell) and INTR is caught
and ignored (so that wait is interruptible). In all cases,
QUIT is ignored by the shell.
-r If the -r flag is present the shell is a restricted shell.
The remaining flags and arguments are described under the set command
above. The command is used to set up login names and execution envi‐
ronments whose capabilities are more controlled than those of the stan‐
dard shell. The actions of are identical to those of sh, except that
the following are disallowed:
changing directory (see cd(1)),
setting the value of SHELL, ENV, or PATH,
specifying path or command names containing /,
redirecting output (>, >| , <> , and >>).
The restrictions above are enforced after .profile and the ENV files
are interpreted.
When a command to be executed is found to be a shell procedure, invokes
to execute it. Thus, it is possible to provide to the end-user shell
procedures that have access to the full power of the standard shell,
while imposing a limited menu of commands; this scheme assumes that the
end-user does not have write and execute permissions in the same direc‐
tory.
The net effect of these rules is that the writer of the .profile has
complete control over user actions, by performing guaranteed setup
actions and leaving the user in an appropriate directory (probably not
the login directory).
The system administrator often sets up a directory of commands (that
is, /usr/rbin) that can be safely invoked by Some systems also provide
a restricted editor red.
Restrictions
If a command which is a tracked alias is executed, and then a command
with the same name is installed in a directory in the search path
before the directory where the original command was found, the shell
will continue to exec the original command. Use the -t option of the
alias command to correct this situation.
Some very old shell scripts contain a ^ as a synonym for the pipe char‐
acter. ⎪.
Using the fc built-in command within a compound command will cause the
whole command to disappear from the history file.
The built-in command . file reads the whole file before any commands
are executed. Therefore, alias and unalias commands in the file will
not apply to any functions defined in the file.
Traps are not processed while a job is waiting for a foreground
process. Thus, a trap on CHLD will not be executed until the fore‐
ground job terminates.
If PWD is not defined in your environment, and a script is run from a
subdirectory with a dot relative path (for example, ../foo) with the
following command, does not understand where the dot (.) path is
located:
cd .
Define PWD in your environment if you use or If you run PWD is set for
you. You can set it to anything as long as it exists in the environ‐
ment.
Exit Status
Errors detected by the shell, such as syntax errors, cause the shell to
return a non-zero exit status. Otherwise, the shell returns the exit
status of the last command executed (see also the exit command above).
If the shell is being used non-interactively then execution of the
shell file is abandoned. Run time errors detected by the shell are
reported by printing the command or function name and the error condi‐
tion. If the line number that the error occurred on is greater than
one, then the line number is also printed in square brackets ([]) after
the command or function name.
Files
See Also
cat(1), cd(1), chmod(1),
cut(1), echo(1), env(1),
stty(1), test(1), umask(2),
vi(1), dup(2), execl(3),
fork(2), ioctl(2), lseek(2),
paste(1), pipe(2), signal(3),
ulimit(3), wait(2), rand(3),
a.out(5), mh_profile(5mh),
environ(7).
Morris I. Bolsky and David G. Korn,
The KornShell Command and Program‐
ming Language, Prentice Hall, 1989.
ksh(1)
