ksh(1) UNIX System V(User Environment Utilities) 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 of && and ||.
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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
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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).
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
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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.
${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)}
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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
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
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printing select lists.
EDITOR
If the value of this variable ends in 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 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
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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 ``> ''.
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 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.
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.
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* 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 (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.
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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 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.
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-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.
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.
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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.
>|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:
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... 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 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, †, 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:
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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 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.
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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 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 it, 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
it, when it is followed by &) and the job monitor option is not active,
the command receives INTERRUPT or QUIT signals but ignores them.
Otherwise, signals have the values inherited by the shell from its parent
(but see also the trap command below).
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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/.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 the vi option
is active, the user can edit the command line. To be in this edit mode
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set the vi 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 mode implements 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 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).
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\ Escape the next erase or kill character.
Motion Edit Commands
These commands will move the cursor.
[count]l Cursor forward (right) one character.
[count]w Cursor forward one alpha-numeric word.
[count]W Cursor to the beginning of the next word that follows a
blank.
[count]e Cursor to end of word.
[count]E Cursor to end of the current blank delimited word.
[count]h Cursor backward (left) one character.
[count]b Cursor backward one word.
[count]B Cursor to preceding blank separated word.
[count]| Cursor to column count.
[count]fc Find the next character c in the current line.
[count]Fc Find the previous character c in the current line.
[count]tc Equivalent to f followed by h.
[count]Tc Equivalent to F followed by l.
[count]; Repeats count times, the last single character find
command, f, F, t, or T.
[count], Reverses the last single character find command count
times.
0 Cursor to start of line.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is entered the
previous command back in time is accessed.
[count]- Equivalent to k.
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[count]j Fetch next command. Each time j is entered the next
command forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The default is the
least recent history command.
/string Search backward through history for a previous command
containing string. String is terminated by a "RETURN" or
"NEW LINE". If string is preceded by a ^, the matched
line must begin with string. If string is null the
previous string will be used.
?string Same as / except that search will be in the forward
direction.
n Search for next match of the last pattern to / or ?
commands.
N Search for next match of the last pattern to / or ?, but
in reverse direction. Search history for the string
entered by the previous / command.
Text Modification Edit Commands
These commands will modify the line.
a Enter input mode and enter text after the current
character.
A Append text to the end of the line. Equivalent to $a.
[count]cmotion
c[count]motion
Delete current character through the character that
motion would move the cursor to and enter input mode. If
motion is c, the entire line will be deleted and input
mode entered.
C Delete the current character through the end of line and
enter input mode. Equivalent to c$.
S Equivalent to cc.
D Delete the current character through the end of line.
Equivalent to d$.
[count]dmotion
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d[count]motion
Delete current character through the character that
motion would move to. If motion is d, the entire line
will be deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line. Equivalent
to 0i.
[count]P Place the previous text modification before the cursor.
[count]p Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen
with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the current
cursor position with c, and advance the cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]~ Invert the case of the count character(s) starting at the
current cursor position and advance the cursor.
[count] Causes the count word of the previous command to be
appended and input mode entered. The last word is used
if count is omitted.
* Causes an * to be appended to the current word and file
name generation attempted. If no match is found, it
rings the bell. Otherwise, the word is replaced by the
matching pattern and input mode is entered.
\ Filename completion. Replaces the current word with the
longest common prefix of all filenames matching the
current word with an asterisk appended. If the match is
unique, a / is appended if the file is a directory and a
space is appended if the file is not a directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
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y[count]motion
Yank current character through character that motion
would move the cursor to and puts them into the delete
buffer. The text and cursor are unchanged.
Y Yanks from current position to end of line. Equivalent
to y$.
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.
@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.
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† : [ 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, 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
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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.
† 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
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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.
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.
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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 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.
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† 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
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.
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.
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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.
-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
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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 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.
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-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).
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 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)
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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 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:
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-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.
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 (i.e.,
/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. 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
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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
SEE ALSO
cat(1), cd(1), chmod(1), cut(1), echo(1), env(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) in the Programmer's Reference
Manual.
newgrp(1M), a.out(4), profile(4), and environ(4) in the System
Administrator's Reference Manual.
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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