ksh(1) 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:
; & ( ) | < > newline 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].
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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 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 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 newlines 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
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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 Filename 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.
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.
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[[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 newline 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 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).
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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.
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In addition, tilde substitution is attempted when the value of
a variable assignment begins with a ~.
Command Substitution
The standard output from a command enclosed in parentheses
preceded by a dollar sign ( $() ) or a pair of backquotes (``)
may be used as part or all of a word; trailing newlines 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] ...
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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 @, 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.
${parameter:+word}
If parameter is set and is non-null then substitute
word; otherwise substitute nothing.
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${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.
- 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
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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.
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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.
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
newline-used to separate command words that 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.
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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 $_.
PATH The search path for commands (see Execution
below). The user may not change PATH if executing
under rksh (except in .profile).
PS1 The value of this variable is expanded for
parameter substitution to define the primary
prompt string which by default is ``$ ''. The
character ! in the primary prompt string is
replaced by the command number (see Command Re-
entry below).
PS2 Secondary prompt string, by default ``> ''.
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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 )
are retained. Implicit null arguments (those resulting from
parameters that have no values) are removed.
Filename 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
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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 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 (that is, made to stand for itself) by preceding it
with a \. The pair \newline 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
backquotes (``) \ quotes the characters \, `, and $. If the
grave quotes occur within double quotes then \ also quotes the
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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 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 newline is typed and further input is needed to
complete a command, then the secondary prompt (that is, the
value of PS2) is issued.
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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
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invoked command. Command and parameter substitution occur
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.
>|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,
\newline 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.
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<&- 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 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
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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,
-, 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).
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
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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
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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 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
When a command is run in the background (that is, when it is
followed by &) and the job monitor option is active, the
command does not receive INTERRUPT or QUIT signals. When a
command is run in the background (that is, when it is followed
by &) and the job monitor option is not active, the command
receives INTERRUPT or QUIT signals but ignores them.
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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 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/.sh_history 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
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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 newline (`RETURN' or `LINE FEED').
If the emacs, gmacs, or vi option is active, the user can edit
the command line. To be in any 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 any 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.
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.
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
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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.
[count]w Cursor forward one alpha-numeric word.
[count]W Cursor to the beginning of the next word that
follows a blank.
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[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.
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[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$.
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[count]dmotion
d[count]motion
Delete current character through the character that
motion would move to. If motion is d, the entire
line will be deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line.
Equivalent to 0i.
[count]P Place the previous text modification before the
cursor.
[count]p Place the previous text modification after the
cursor.
R Enter input mode and replace characters on the
screen with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the
current cursor position with c, and advance the
cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]~ Invert the case of the count character(s) starting
at the current cursor position and advance the
cursor.
[count]_ Causes the count word of the previous command to be
appended and input mode entered. The last word is
used if count is omitted.
* Causes an * to be appended to the current word and
file name generation attempted. If no match is
found, it rings the bell. Otherwise, the word is
replaced by the matching pattern and input mode is
entered.
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\ Filename completion. Replaces the current word with
the longest common prefix of all filenames matching
the current word with an asterisk appended. If the
match is unique, a / is appended if the file is a
directory and a space is appended if the file is not
a directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that motion
would move the cursor to and puts them into the
delete buffer. The text and cursor are unchanged.
Y Yanks from current position to end of line.
Equivalent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on
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.
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@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.
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.
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^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 previous 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 ^U 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).
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^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-
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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 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.
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M-# Insert a # at the beginning of the line and execute
it. This causes a comment to be inserted in the
history file.
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 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,
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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.
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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.
- 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
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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 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.
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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 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 newline 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
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does not signify line continuation. The first field is
assigned to the first name, the second field to the
second name, and so on, 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.
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-k All variable 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 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.
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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). When
the -p flag is not present, the shell will set the
effective uid and gid to the real uid and gid if
they don't match and if the effective uid is <100.
When the effective uid is >=100, the effective gid
is not set to the real gid. When the effective
uid is <100 and is set to the real uid and ksh is
invoked without -p flag, set -p and set +p have no
effect.
-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 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 $#.
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- 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:
-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
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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] ]
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).
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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
a privileged user may raise a hard limit; see su(1M).
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 variables cannot be unset. If the flag, -f, is
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set, then the names refer to function names. Unsetting
ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM,
SECONDS, TMOUT, and _ 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
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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.
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
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, 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
(that is, /usr/rbin) that can be safely invoked by rksh.
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.
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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/suid_profile
$HOME/.profile
/tmp/sh*
/dev/null
/usr/lib/locale/locale/LC_MESSAGES/uxue
language-specific message file [See LANG on environ(5).]
REFERENCES
a.out(4), cat(1), cd(1), chmod(1), cut(1), dup(2), echo(1),
env(1), environ(5), exec(2), fork(2), ioctl(2), lseek(2),
newgrp(1M), paste(1), pipe(2), profile(4), rand(3C),
signal(2), stty(1), test(1), ulimit(2), umask(1), umask(2),
vi(1), wait(2)
Morris I. Bolsky and David G. Korn, The KornShell Command and
Programming Language, Prentice Hall, 1989
NOTICES
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.
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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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