ksh(1) DG/UX 5.4.2 ksh(1)
NAME
ksh, rksh - KornShell, a standard/restricted command and programming
language
SYNOPSIS
ksh [ ±aefhikmnprstuvx ] [ ±o option ] ... [ -c string ] [ arg ... ]
rksh [ ±aefhikmnprstuvx ] [ ±o option ] ... [ -c string ] [ arg ... ]
DESCRIPTION
Ksh is a command and programming language that executes commands read
from a terminal or a file. rksh 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 below for the meaning of
arguments 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.
Identifiers are used as names for functions and variables. 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
language. 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 separate process. Except for documented side effects,
most special commands can be implemented as separate utilities.
Commands.
A simple-command is a sequence of blank separated words which may be
preceded by a variable 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
exec(2)]. The value of a simple-command is its exit status if it
terminates normally, or (octal) 200+status if it terminates
abnormally [see signal(2) 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
pipe(2) to the standard input of the next command. Each command is
run as a separate process; the shell waits for the last command to
terminate. The exit status of a pipeline is the exit status of the
last command.
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
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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 (i.e., 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 output of the spawned command can be written to
and read from by the parent 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
omitted, then the for command executes the do list once for
each positional parameter that is set (see Parameter
Substitution below). 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 variable 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
pattern 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.
Otherwise, 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.
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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
adjacent open parentheses are needed for nesting, a space must
be inserted to avoid arithmetic evaluation as described below.
{ list;}
list is simply executed. The { must be followed by a space.
Note that unlike the metacharacters ( and ), { and } are
reserved words and must be typed at the beginning of a line or
after a ; in order to be recognized.
[[expression]]
Evaluates expression and returns a zero exit status when
expression is true. See Conditional Expressions below, 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). The { must be followed by a space.
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 [[ ]]
Comments.
A word beginning with # causes that word and all the following
characters 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. An alias name consists of
any number of characters excluding meta-characters, quoting
characters, file expansion characters, parameter and command
substitution characters and =. 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
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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 special builtin
commands but cannot be used to redefine the reserved words listed
above. Aliases can be created, listed, and exported with the alias
command and can be removed with the unalias 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
executed. 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 set 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 /etc/passwd file. If
a match is found, the ~ and the matched login name is replaced by the
login directory 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 $HOME.
A ~ followed by a + or - is replaced by $PWD and $OLDPWD
respectively.
In addition, tilde substitution is attempted when the value of a
variable assignment begins with a ~.
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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 below). The command substitution $(cat file) can be replaced
by the equivalent but faster $(<file). Command substitution of most
special commands that do not perform input/output redirection are
carried out without creating a separate process.
An arithmetic expression enclosed in double parentheses and preceded
by a dollar sign [$(())] is replaced by the value of the arithmetic
expression within the double parentheses.
Parameter Substitution.
A parameter is an identifier, one or more digits, or any of the
characters *, @, #, ?, -, $, and !. A variable (a parameter denoted
by an identifier) has a value and zero or more attributes. Variables
can be assigned values and attributes by using the typeset special
command. The attributes supported by the Shell are described later
with the typeset special command. Exported parameters pass values
and attributes to the environment.
The shell supports a one-dimensional array facility. An element of
an array variable is referenced by a subscript. A subscript is
denoted by a [, followed by an arithmetic expression (see Arithmetic
Evaluation below) 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 variable 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 variable 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 set 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
followed by a letter, digit, or underscore that is not to be
interpreted as part of its name or when a variable 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 @,
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then all the positional parameters, starting with $1, are
substituted (separated by a field separator character). If an
array identifier with subscript * 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 positional 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 substitute 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 substitute 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 substitute 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 substitution 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
substituted string, so that, in the following example, pwd 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.
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- Flags supplied to the shell on invocation or by the set
command.
? 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
environment. Subsequently it is assigned the last
argument of the previous command. This parameter is
not set for commands which are asynchronous. This
parameter is also used to hold the name of the matching
MAIL 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 cd command.
OPTARG The value of the last option argument processed by the
getopts special command.
OPTIND The index of the last option argument processed by the
getopts special command.
PPID The process number of the parent of the shell.
PWD The present working directory set by the cd command.
RANDOM Each time this variable is referenced, a random
integer, uniformly distributed between 0 and 32767, is
generated. The sequence of random numbers can be
initialized by assigning a numeric value to RANDOM.
REPLY This variable is set by the select statement and by the
read special command when no arguments are supplied.
SECONDS
Each time this variable is referenced, the number of
seconds since shell invocation is returned. If this
variable 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 variables are used by the shell:
CDPATH The search path for the cd 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
corresponding option (see Special Command set below)
will be turned on.
ENV If this variable 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.
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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
referenced and when a command is not found. If an
executable file is found, then it is read and executed
in the current 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
separating words with the special command read. The
first character of the IFS variable is used to separate
arguments for the "$*" substitution (see Quoting
below).
HISTFILE
If this variable 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 variable 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
command.
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.
MAIL If this variable is set to the name of a mail file and
the MAILPATH variable 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
variables. 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
variable 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 variable, $ defined as the name of the file that
has changed. The default message is you have mail in
$.
PATH The search path for commands (see Execution below).
The user may not change PATH if executing under rksh
(except in .profile).
PS1 The value of this variable is expanded for parameter
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substitution to define the primary prompt string which
by default is ``$ ''. 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 variable 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
terminate 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. HOME, MAIL and SHELL are 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 characters appears then the word is regarded as a pattern. The
word is replaced with lexicographically sorted file names that match
the pattern. 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 specially.
* Matches any string, including the null string.
? Matches any single character.
[...] Matches any one of the enclosed characters. A pair of
characters 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
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character.
A pattern-list is a list of one or more patterns separated from 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 (i.e., made to stand for itself)
by preceding it with a \. The pair \new-line is removed. All
characters 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 $@
is identical when not quoted or when used as a variable assignment
value or as a file name. However, when used as a command argument,
"$*" is equivalent to "$1d$2d...", where d is the first character of
the IFS variable, whereas "$@" is equivalent to "$1"d"$2"d... 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
function 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.
Constants 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
associativity of expression of the C language. All the integral
operators, other than ++, --, ?:, and , are supported. Variables can
be referenced by name within an arithmetic expression without using
the parameter substitution syntax. When a variable is referenced,
its value is evaluated as an arithmetic expression.
An internal integer representation of a variable can be specified
with the -i option of the typeset special command. Arithmetic
evaluation is performed on the value of each assignment to a variable
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with the -i attribute. If you do not specify an arithmetic base, the
first assignment to the variable 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 parameter
expanded 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 (i.e., 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 effective
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.
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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, is a regular file, and the noclobber
option is on, this causes an error; otherwise, it is
truncated to zero length.
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>|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 characters of the
document; otherwise, parameter and command substitution
occurs, \new-line is ignored, and \ must be used to
quote the characters \, $, `, and the first character
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 (i.e. fname). If the order of redirections were
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reversed, file descriptor 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(5)] is a list of name-value pairs that
is passed to an executed program in the same way as a normal argument
list. The 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 variable
for each name found, giving it the corresponding value and marking it
export. Executed commands inherit the environment. If the user
modifies the values of these variables 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 modified 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 variable assignments. A variable
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
except for commands listed with one or two daggers, † or ‡, in the
Special Commands section).
If the -k flag is set, all variable assignment arguments are placed
in the environment, even if they occur after the command name. The
following 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
versions 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. Functions are executed like commands with the arguments passed
as positional parameters (see Execution below).
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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 may 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 numbers. 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.
If you are running a job and wish to do something else you may hit
the key ^Z (ctrl-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
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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
triggers 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
command 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
command name is checked to see if it matches one of the user defined
functions. 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 command or a user defined function, a process
is created and an attempt is made to execute the command via exec(2).
The shell variable PATH defines the search path for the directory
containing the command. Alternative directory names are separated by
a colon (:). The default path is /usr/bin: (specifying /usr/bin and
the current directory in that order). The current directory can be
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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
permission 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 variables, are removed
in this case. 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/.shhistory is used if the file denoted by 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 characters 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 variable FCEDIT is used. If FCEDIT is not defined then
/usr/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
substitution variable of the form old=new can be used to modify the
command 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 VISUAL 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
overwrite 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.
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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 example, ^F is the notation for CTRL-f. This is
entered by depressing `f' while holding down the `CTRL' (control)
key. (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)
command, 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
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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 terminals).
^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 forward. 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
asterisk is appended if the word doesn't match any file or
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contain 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-# Insert a # 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 second has elapsed since the prompt was printed. The ESC
character terminates 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
canonical processing disabled.
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.
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[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
$a.
[count]cmotion
c[count]motion
Delete current character through the character that
motion would move the cursor to and enter input
mode. If motion is c, the entire line will be
deleted and input mode entered.
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C Delete the current character through the end of line
and enter input mode. Equivalent to c$.
S Equivalent to cc.
D Delete the current character through the end of
line. Equivalent to d$.
[count]dmotion
d[count]motion
Delete current character through the character that
motion would move to. If motion is d, the entire
line will be deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line.
Equivalent to 0i.
[count]P Place the previous text modification before the
cursor.
[count]p Place the previous text modification after the
cursor.
R Enter input mode and replace characters on the
screen with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the
current cursor position with c, and advance the
cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]~ Invert the case of the count character(s) starting
at the current cursor position and advance the
cursor.
[count] Causes the count word of the previous command to be
appended and input mode entered. The last word is
used if count is omitted.
* Causes an * to be appended to the current word and
file name generation attempted. If no match is
found, it rings the bell. Otherwise, the word is
replaced by the matching pattern and input mode is
entered.
\ Filename completion. Replaces the current word with
the longest common prefix of all filenames matching
the current word with an asterisk appended. If the
match is unique, a / is appended if the file is a
directory and a space is appended if the file is not
a directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that motion
would move the cursor to and puts them into the
delete buffer. The text and cursor are unchanged.
Y Yanks from current position to end of line.
Equivalent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on
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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
processing.
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. Variable assignment lists preceding the command remain in
effect when the command completes.
2. I/O redirections are processed after variable 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 variable assignment, are expanded with the same
rules as a variable assignment. This means that tilde
substitution is performed after the = sign and word splitting
and file name generation 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
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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 remain 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
enclosing 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
directory is changed to the previous directory. The shell
variable HOME is the default arg. The variable PWD is set to
the current directory. The shell variable 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 rksh.
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.
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† exec [ arg ... ]
If arg is given, the command specified by the arguments is
executed 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
environment 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 number is used as an offset to the current command
number. If the flag -l, is selected, the commands are listed
on standard output. Otherwise, the editor program ename is
invoked on a file containing these keyboard commands. If
ename is not supplied, then the value of the variable FCEDIT
(default /usr/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-executed 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 current 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 recognizes. If a letter is followed by a :, that
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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.
Otherwise, 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 (terminate) 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 /usr/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
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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 output.
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
continuation. The first field is assigned to the first name,
the second 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 interactive. The exit status is 0
unless an end-of-file is encountered.
†† 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 [ ±aefhkmnpstuvx ] [ ±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 variables that are defined are
automatically 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
encountered.
-k All variable assignment arguments are placed in the
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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
automatically 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/suidprofile 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.
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-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 variables are printed
on the standard output.
† shift [ n ]
The positional parameters from $n+1 ... are renamed $1 ... ,
default n is 1. The parameter n can be any arithmetic
expression 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 executed in order of signal number. Any attempt
to set a trap on a signal that was ignored on entry to the
current shell is ineffective. 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 command with no arguments prints a
list of commands associated with each signal number.
†† typeset [ ±HLRZfilrtux[n] ] [ name[ =value ] ] ...
Sets attributes and values for shell variables. When invoked
inside a function, a new instance of the variable name is
created. The parameter value and type are restored when the
function completes. The following list of attributes may be
specified:
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-H This flag provides UNIX to host-name file mapping on
non-UNIX 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 variable is assigned to, it
is filled on the right with blanks or truncated, if
necessary, 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 variable 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 variable
names. No assignments can be made and the only other
valid flags are -t, -u and -x. The flag -t turns on
execution 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 Variable 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
cannot be changed by subsequent assignment.
-t Tags the variables. 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 variables 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 variables are printed.
ulimit [ -[HS][a | cdfnstv] ]
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ulimit [ -[HS][c | d | f | n | s | t | v] ] limit
ulimit prints or sets hard or soft resource limits. These
limits are described in getrlimit(2).
If limit is not present, ulimit prints the specified limits.
Any number of limits may be printed at one time. The -a
option prints all limits.
If limit is present, ulimit sets the specified limit to limit.
The string unlimited requests the largest valid limit. Limits
may be set for only one resource at a time. Any user may set
a soft limit to any value below the hard limit. Any user may
lower a hard limit. Only the super-user may raise a hard
limit; see su(1).
The -H option specifies a hard limit. The -S option specifies
a soft limit. If neither option is specified, ulimit will set
both limits and print the soft limit.
The following options specify the resource whose limits are to
be printed or set. If no option is specified, the file size
limit is printed or set.
-c maximum core file size (in 512-byte blocks)
-d maximum size of data segment or heap (in kbytes)
-f maximum file size (in 512-byte blocks)
-n maximum file descriptor plus 1
-s maximum size of stack segment (in kbytes)
-t maximum CPU time (in seconds)
-v maximum size of virtual memory (in kbytes)
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 complement of the previous umask value. If mask is
omitted, the current value of the mask is printed.
unalias name ...
The variables given by the list of names are removed from the
alias list.
unset [ -f ] name ...
The variables given by the list of names are unassigned, i.
e., their values and attributes are erased. Read-only
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variables cannot 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 special 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
format of job.
whence [ -pv ] name ...
For each name, indicate how it would be interpreted if used as
a command name.
-v produces a more verbose report.
-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 commands are read from /etc/profile and then from either
.profile in the current directory or $HOME/.profile, if either file
exists. Next, commands are read from the file named by performing
parameter substitution on the value of the environment variable 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 setgid settings will be ignored. Commands are then
read as described below; the following 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
commands are read from the standard input. Shell output,
except for the output of the Special commands listed above,
is written 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.
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Rksh Only.
Rksh is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
The actions of rksh are identical to those of ksh, 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, rksh
invokes ksh 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 directory.
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 (i.e.,
/usr/rbin) that can be safely invoked by rksh.
EXIT CODES
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 condition. 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
/etc/passwd
/etc/profile
/etc/suidprofile
$HOME/.profile
/tmp/sh*
/dev/null
SEE ALSO
cat(1), cd(1), chmod(1), cut(1), echo(1), emacs(1), env(1), gmacs(1),
paste(1), stty(1), test(1), umask(1), and vi(1).
dup(2), exec(2), fork(2), ioctl(2), lseek(2), pipe(2), signal(2),
umask(2), ulimit(2), wait(2), and rand(3C).
newgrp(1M), a.out(4), profile(4), and environ(4).
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Morris I. Bolsky and David G. Korn, The KornShell Command and
Programming Language, Prentice Hall, 1989.
NOTES
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
character. |.
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 won't be executed until the foreground
job terminates.
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