KSH(C) UNIX System V
Name
ksh, rksh - KornShell, a standard/restricted command and
programming language
Syntax
ksh [ +aefhikmnoprstuvx ] [ +o option ] ... [ -c string ]
[ arg ... ]
rksh [ +aefhikmnoprstuvx ] [ +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
named parameters. A word is a sequence of characters
separated by one or more non-quoted metacharacters.
A command is a sequence of characters in the syntax of the
shell 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 parameter assignment list. (See
Environment below). The first word specifies the name of
the command to be executed. Except as specified below, the
remaining words are passed as arguments to the invoked
command. The command name is passed as argument 0 (see
exec(S)). The value of a simple-command is its exit status
if it terminates normally, or (octal) 200+status if it
terminates abnormally (see signal(S) 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(S) 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 (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 parameter REPLY. The list is executed for
each selection until a break or end-of-file is
encountered.
case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
A case command executes the list associated with the
first 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.
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. Note that unlike the
metacharacters ( and ), { and } are reserved words and
must at the beginning of a line or after a ; in order
to be recognized.
[[expression]]
Evaluates expression and returns a zero exit status
when 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).
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. The first
character of an alias name can be any non-special printable
character, but the rest of the characters must be the same
as for a valid identifier. The replacement string can
contain any valid Shell script including the metacharacters
listed above. The first word of each command in the
replaced text, other than any that are in the process of
being replaced, will be tested for aliases. If the last
character of the alias value is a blank then the word
following the alias will also be checked for alias
substitution. Aliases can be used to redefine 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 the value of the HOME parameter. A ~ followed
by a + or - is replaced by $PWD and $OLDPWD respectively.
In addition, tilde substitution is attempted when the value
of a variable assignment parameter begins with a ~.
Command Substitution
The standard output from a command enclosed in parenthesis
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 parenthesis
preceded by a dollar sign ( $(()) ) is replaced by the value
of the arithmetic expression within the double parenthesis.
Parameter Substitution
A parameter is an identifier, one or more digits, or any of
the characters *, @, #, ?, -, $, and !. A named parameter
(a parameter denoted by an identifier) has a value and zero
or more attributes. Named parameters can be assigned values
and attributes by using the 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 parameter 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 named parameter with a valid
subscript is legal and an array will be created if
necessary. Referencing an array without a subscript is
equivalent to referencing the element zero.
The value of a named parameter may also be assigned by
writing:
name=value [ name=value ] ...
If the integer attribute, -i, is set for name the value is
subject to arithmetic evaluation as described below.
Positional parameters, parameters denoted by a number, may
be assigned values with the 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 named parameter is subscripted. If parameter is
one or more digits then it is a positional parameter.
A positional parameter of more than one digit must be
enclosed in braces. If parameter is * or @, then all
the positional parameters, starting with $1, are
substituted (separated by a field separator character).
If an array identifier with subscript * or @ is used,
then the value for each of the elements is substituted
(separated by a field separator character).
${#parameter}
If parameter is * or @, the number of positional
parameters is substituted. Otherwise, the length of
the value of the parameter is substituted.
${#identifier[*]}
The number of elements in the array identifier is
substituted.
${parameter:-word}
If parameter is set and is non-null then substitute its
value; otherwise substitute word.
${parameter:=word}
If parameter is not set or is null then set it to word;
the value of the parameter is then substituted.
Positional parameters may not be assigned to in this
way.
${parameter:?word}
If parameter is set and is non-null then substitute its
value; otherwise, print word and exit from the shell.
If word is omitted then a standard message is printed.
${parameter:+word}
If parameter is set and is non-null then substitute
word; otherwise substitute nothing.
${parameter#pattern}
${parameter##pattern}
If the Shell pattern matches the beginning of the value
of parameter, then the value of this substitution is
the value of the parameter with the matched portion
deleted; otherwise the value of this parameter is
substituted. In the first form the smallest matching
pattern is deleted and in the second form the largest
matching pattern is deleted.
${parameter%pattern}
${parameter%%pattern}
If the Shell pattern matches the end of the value of
parameter, then the value of this substitution is the
value of the parameter with the matched part deleted;
otherwise substitute the value of parameter. In the
first form the smallest matching pattern is deleted and
in the second form the largest matching pattern is
deleted.
In the above, word is not evaluated unless it is to be used
as the substituted string, so that, in the following
example, pwd is executed only if d is not set or is null:
echo ${d:-$(pwd)}
If the colon ( : ) is omitted from the above expressions,
then the shell only checks whether parameter is set or not.
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
- 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 parameter 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 parameter is set by the select statement and
by the read special command when no arguments are
supplied.
SECONDS
Each time this parameter is referenced, the number
of seconds since shell invocation is returned. If
this parameter is assigned a value, then the value
returned upon reference will be the value that was
assigned plus the number of seconds since the
assignment.
The following parameters are used by the shell:
CDPATH
The search path for the 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 parameter is set, then parameter
substitution is performed on the value to generate
the pathname of the script that will be executed
when the shell is invoked. (See Invocation
below.) This file is typically used for alias and
function definitions.
FCEDIT
The default editor name for the fc command.
FPATH
The search path for function definitions. This
path is searched when a function with the -u
attribute is 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 parameter is used to separate arguments for
the "$*" substitution (See Quoting below).
HISTFILE
If this parameter is set when the shell is
invoked, then the value is the pathname of the
file that will be used to store the command
history. (See Command re-entry below.)
HISTSIZE
If this parameter is set when the shell is
invoked, then the number of previously entered
commands that are accessible by this shell will be
greater than or equal to this number. The default
is 128.
HOME The default argument (home directory) for the cd
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 parameter is set to the name of a mail
file and the MAILPATH parameter is not set, then
the shell informs the user of arrival of mail in
the specified file.
MAILCHECK
This variable specifies how often (in seconds) the
shell will check for changes in the modification
time of any of the files specified by the MAILPATH
or MAIL parameters. The default value is 600
seconds. When the time has elapsed the shell will
check before issuing the next prompt.
MAILPATH
A colon ( : ) separated list of file names. If
this parameter is set then the shell informs the
user of any modifications to the specified files
that have occurred within the last MAILCHECK
seconds. Each file name can be followed by a ?
and a message that will be printed. The message
will undergo parameter substitution with the
parameter, $ defined as the name of the file that
has changed. The default message is you have mail
in $_.
PATH The search path for commands (see Execution
below). The user may not change PATH if executing
under rksh (except in .profile ).
PS1 The value of this parameter is expanded for
parameter substitution to define the primary
prompt string which by default is ``$ ''. The
character ! in the primary prompt string is
replaced by the command number (see Command Re-
entry below).
PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop,
by default ``#? ''.
PS4 The value of this parameter is expanded for
parameter substitution and precedes each line of
an execution trace. If omitted, the execution
trace prompt is ``+ ''.
SHELL
The pathname of the shell is kept in the
environment. At invocation, if the basename of
this variable matches the pattern *r*sh, then the
shell becomes restricted.
TMOUT
If set to a value greater than zero, the shell
will 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, while HOME, SHELL ENV and MAIL are not set at
all by the shell (although HOME is set by login(M)). On
some systems MAIL and SHELL are also set by login(M)).
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.
* 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
by each other with a |. Composite patterns can be formed
with one or more of the following:
?(pattern-list)
Optionally matches any one of the given patterns.
*(pattern-list)
Matches zero or more occurrences of the given patterns.
+(pattern-list)
Matches one or more occurrences of the given patterns.
@(pattern-list)
Matches exactly one of the given patterns.
!(pattern-list)
Matches anything, except one of the given patterns.
Quoting
Each of the metacharacters listed above (See Definitions
above) has a special meaning to the shell and causes
termination of a word unless quoted. A character may be
quoted (i.e., made to stand for itself) by preceding it with
a \. The pair \new-line is ignored. 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 $@ is identical when not
quoted or when used as a parameter assignment value or as a
file name. However, when used as a command argument, "$*"
is equivalent to "$1d$2d...", where d is the first character
of the IFS parameter, whereas "$@" is equivalent to "$1"
"$2" .... Inside grave quote marks (``) \ quotes the
characters \, `, and $. If the grave quotes occur within
double quotes then \ also quotes the character ".
The special meaning of reserved words or aliases can be
removed by quoting any character of the reserved word. The
recognition of 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. Named parameters can be referenced by name
within an arithmetic expression without using the parameter
substitution syntax. When a named parameter is referenced,
its value is evaluated as an arithmetic expression.
An internal integer representation of a named parameter can
be specified with the -i option of the typeset special
command. Arithmetic evaluation is performed on the value of
each assignment to a named parameter with the -i attribute.
If you do not specify an arithmetic base, the first
assignment to the parameter determines the arithmetic base.
This base is used when parameter substitution occurs.
Since many of the arithmetic operators require quoting, an
alternative form of the let command is provided. For any
command which begins with a ((, all the characters until a
matching )) are treated as a quoted expression. More
precisely, ((...)) is equivalent to let "...".
Prompting
When used interactively, the shell prompts with the value of
PS1 before reading a command. If at any time a new-line is
typed and further input is needed to complete a command,
then the secondary prompt (i.e., the value of PS2) is
issued.
Conditional Expressions
A conditional expression is used with the [[ compound
command to test attributes of files and to compare strings.
Word splitting and file name generation are not performed on
the words between [[ and ]]. Each expression can be
constructed from one or more of the following unary or
binary expressions:
-a file
True, if file exists.
-b file
True, if file exists and is a block special file.
-c file
True, if file exists and is a character special file.
-d file
True, if file exists and is a directory.
-f file
True, if file exists and is an ordinary file.
-g file
True, if file exists and is has its setgid bit set.
-k file
True, if file exists and is has its sticky bit set.
-n string
True, if length of string is non-zero.
-o option
True, if option named option is on.
-p file
True, if file exists and is a fifo special file or a
pipe.
-r file
True, if file exists and is readable by current
process.
-s file
True, if file exists and has size greater than zero.
-t fildes
True, if file descriptor number fildes is open and
associated with a terminal device.
-u file
True, if file exists and is has its setuid bit set.
-w file
True, if file exists and is writable by current
process.
-x file
True, if file exists and is executable by current
process. If file exists and is a directory, then the
current process has permission to search in the
directory.
-z string
True, if length of string is zero.
-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.
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.
Spelling Checker
By default, the shell checks spelling whenever you use cd to
change directories. For example, if you change to a
different directory using cd and misspell the directory
name, the shell responds with an alternative spelling of an
existing directory. Enter ``y'' and press RETURN (or just
press RETURN) to change to the offered directory. If the
offered spelling is incorrect, enter ``n'', then retype the
command line. In this example the ksh response is
boldfaced:
# cd /usr/spol/uucp
/usr/spool/uucp? y
ok
The spell check feature is controlled by the CDSPELL
environment variable. The default value of CDSPELL is set
to the string ``cdspell'' whenever a ksh session is run. A
user can change it to any value, including the null string,
but the value is immaterial, if CDSPELL is set to any value,
the spell check feature is engaged.
To disable the spelling checker, enter the following at the
ksh prompt :
unset CDSPELL
(Reg.).DE
When the user does a set at the ksh prompt,
CDSPELL is not listed if the unset was successful.
Input/Output
Before a command is executed, its input and output may be
redirected using a special notation interpreted by the
shell. The following may appear anywhere in a simple-
command or may precede or follow a command and are not
passed on to the invoked command. Command and parameter
substitution occurs before word or digit is used except as
noted below. File name generation occurs only if the
pattern matches a single file and blank interpretation is
not performed.
<word Use file word as standard input (file
descriptor 0).
>word Use file word as standard output (file
descriptor 1). If the file does not exist
then it is created. If the file exists, and
the noclobber option is on, this causes an
error; otherwise, it is truncated to zero
length.
>|word Sames as >, except that it overrides the
noclobber option.
>>word Use file word as standard output. If the file
exists then output is appended to it (by first
seeking to the end-of-file); otherwise, the
file is created.
<>word Open file word for reading and writing as
standard input.
<<[-]word The shell input is read up to a line that is
the same as word, or to an end-of-file. No
parameter substitution, command substitution
or file name generation is performed on word.
The resulting document, called a here-
document, becomes the standard input. If any
character of word is quoted, then no
interpretation is placed upon the 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(S)). Similarly for
the standard output using >& digit.
<&- The standard input is closed. Similarly for
the standard output using >&-.
<&p The input from the co-process is moved to
standard input.
>&p The output to the co-process is moved to
standard output.
If one of the above is preceded by a digit, then the file
descriptor number referred to is that specified by the digit
(instead of the default 0 or 1). For example:
... 2>&1
means file descriptor 2 is to be opened for writing as a
duplicate of file descriptor 1.
The order in which redirections are specified is
significant. The shell evaluates each redirection in terms
of the (file descriptor, file) association at the time of
evaluation. For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then
associates file descriptor 2 with the file associated with
file descriptor 1 (i.e. fname). If the order of
redirections were 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(M)) is a list of name-value
pairs that is passed to an executed program in the same way
as a normal argument list. The names must be identifiers
and the values are character strings. The shell interacts
with the environment in several ways. On invocation, the
shell scans the environment and creates a parameter for each
name found, giving it the corresponding value and marking it
export . Executed commands inherit the environment. If the
user modifies the values of these parameters or creates new
ones, using the export or typeset -x commands they become
part of the environment. The environment seen by any
executed command is thus composed of any name-value pairs
originally inherited by the shell, whose values may be
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 parameter
assignments. A parameter assignment argument is a word of
the form identifier=value. Thus:
TERM=450 cmd args and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is
concerned).
If the -k flag is set, all parameter assignment arguments
are placed in the environment, even if they occur after the
command name. The 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 the condition to be passed on to the
caller. A trap on EXIT set inside a function is executed
after the function completes in the environment of the
caller. Ordinarily, variables are shared between the
calling program and the function. However, the typeset
special command used within a function defines local
variables whose scope includes the current function and all
functions it calls.
The special command return is used to return from function
calls. Errors within functions return control to the
caller.
Function identifiers can be listed with the -f or +f option
of the typeset special command. The text of functions will
also be listed with -f. Function can be undefined with the
-f option of the unset special command.
Ordinarily, functions are unset when the shell executes a
shell script. The -xf option of the typeset command allows
a function to be exported to scripts that are executed
without a separate invocation of the shell. Functions that
need to be defined across separate invocations of the shell
should be specified in the ENV file with the -xf option of
typeset
Jobs
If the monitor option of the set command is turned on, an
interactive shell associates a job with each pipeline. It
keeps a table of current jobs, printed by the jobs command,
and assigns them small integer 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 (control-Z) which sends a STOP signal to
the current job. (This is known as the suspend character,
and is ^Z by default; this can be changed in the stty susp
line in a user's .profile file.) 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
The INT and QUIT signals for an invoked command are ignored
if the command is followed by & and job monitor option is
not active. Otherwise, signals have the values inherited by
the shell from its parent (but see also the trap command
below).
Execution
Each time a command is executed, the above substitutions are
carried out. If the command name matches one of the Special
Commands listed below, it is executed within the current
shell process. Next, the command name is checked to see if
it matches one of the user defined functions. If it does,
the positional parameters are saved and then reset to the
arguments of the function call. When the function completes
or issues a return, the positional parameter list is
restored and any trap set on EXIT within the function is
executed. The value of a function is the value of the last
command executed. A function is also executed in the
current shell process. If a command name is not a special
command or a user defined function, a process is created and
an attempt is made to execute the command via exec(S).
The shell parameter PATH defines the search path for the
directory containing the command. Alternative directory
names are separated by a colon (:). The default path is
/bin:/usr/bin: (specifying /bin, /usr/bin, and the current
directory in that order). The current 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 named
parameters are removed in this case. If the shell command
file doesn't have read permission, or if the setuid and/or
setgid bits are set on the file, then the shell executes an
agent whose job it is to set up the permissions and execute
the shell with the shell command file passed down as an open
file. A parenthesized command is executed in a sub-shell
without removing non-exported quantities.
Command Re-entry
The text of the last HISTSIZE (default 128) commands entered
from a terminal device is saved in a history file. The file
$HOME/.shhistory is used if the HISTFILE variable is not
set or is not writable. A shell can access the commands of
all interactive shells which use the same named HISTFILE.
The special command fc is used to list or edit a portion of
this file. The portion of the file to be edited or listed
can be selected by number or by giving the first character
or 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 parameter
FCEDIT is used. If FCEDIT is not defined then /bin/ed is
used. The edited command(s) is printed and re-executed upon
leaving the editor. The editor name - is used to skip the
editing phase and to re-execute the command. In this case a
substitution parameter of the form old=new can be used to
modify the command before execution. For example, if r is
aliased to 'fc -e -' then typing `r bad=good c' will re-
execute the most recent command which starts with the letter
c, replacing the first occurrence of the string bad with the
string good.
In-line Editing Options
Normally, each command line entered from a terminal device
is simply typed followed by a new-line (`RETURN' or
`LINE FEED'). If either the emacs, gmacs, or vi option is
active, the user can edit the command line. To be in either
of these edit modes set the corresponding option. An
editing option is automatically selected each time the
VISUAL or EDITOR variable is assigned a value ending in
either of these option names.
The editing features require that the user's terminal accept
`RETURN' as carriage return without line feed and that a
space (` ') must overwrite the current character on the
screen. ADM terminal users should set the "space - advance"
switch to `space'. Hewlett-Packard series 2621 terminal
users should set the straps to `bcGHxZ etX'.
The editing modes implement a concept where the user is
looking through a window at the current line. The window
width is the value of COLUMNS if it is defined, otherwise
80. If the line is longer than the window width minus two,
a mark is displayed at the end of the window to notify the
user. As the cursor moves and reaches the window boundaries
the window will be centered about the cursor. The mark is a
> (<, *) if the line extends on the right (left, both)
side(s) of the window.
The search commands in each edit mode provide access to the
history file. Only strings are matched, not patterns,
although a leading ^ in the string restricts the match to
begin at the first character in the line.
Emacs Editing Mode
This mode is entered by enabling either the emacs or gmacs
option. The only difference between these two modes is the
way they handle ^T. To edit, the user moves the cursor to
the point needing correction and then inserts or deletes
characters or words as needed. All the editing commands are
control characters or escape sequences. The notation for
control characters is caret ( ^ ) followed by the character.
For example, ^F is the notation for control F. This is
entered by depressing `f' while holding down the `CTRL'
(control) key. The `SHIFT' key is not depressed. (The
notation ^? indicates the DEL (delete) key.)
The notation for escape sequences is M- followed by a
character. For example, M-f (pronounced Meta f) is entered
by depressing ESC (ascii 033) followed by `f'. (M-F would
be the notation for ESC followed by `SHIFT' (capital) `F'.)
All edit commands operate from any place on the line (not
just at the beginning). Neither the "RETURN" nor the "LINE
FEED" key is entered after edit commands except when noted.
^F Move cursor forward (right) one character.
M-f Move cursor forward one word. (The emacs editor's
idea of a word is a string of characters
consisting of only letters, digits and
underscores.)
^B Move cursor backward (left) one character.
M-b Move cursor backward one word.
^A Move cursor to start of line.
^E Move cursor to end of line.
^]char Move cursor forward to character char on current
line.
M-^]char Move cursor back to character char on current
line.
^X^X Interchange the cursor and mark.
erase (User defined erase character as defined by the
stty(C) command, usually ^H or #.) Delete
previous character.
^D Delete current character.
M-d Delete current word.
M-^H (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-DEL) Delete previous word (if your interrupt
character is ^? (DEL, the default) then this
command will not work).
^T Transpose current character with next character in
emacs mode. Transpose two previous characters in
gmacs mode.
^C Capitalize current character.
M-c Capitalize current word.
M-l Change the current word to lower case.
^K Delete from the cursor to the end of the line. If
preceded by a numerical parameter whose value is
less than the current cursor position, then delete
from given position up to the cursor. If preceded
by a numerical parameter whose value is greater
than the current cursor position, then delete from
cursor up to given cursor position.
^W Kill from the cursor to the mark.
M-p Push the region from the cursor to the mark on the
stack.
kill (User defined kill character as defined by the
stty command, usually ^G or @.) Kill the entire
current line. If two kill characters are entered
in succession, all kill characters from then on
cause a line feed (useful when using paper
terminals).
^Y Restore last item removed from line. (Yank item
back to the line.)
^L Line feed and print current line.
^@ (Null character) Set mark.
M-space (Meta space) Set mark.
^J (New line) Execute the current line.
^M (Return) Execute the current line.
eof End-of-file character, normally ^D, is processed
as an End-of-file only if the current line is
null.
^P Fetch previous command. Each time ^P is entered
the previous command back in time is accessed.
Moves back one line when not on the first line of
a multi-line command.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command line. Each time ^N is entered
the next command line forward in time is accessed.
^Rstring Reverse search history for a previous command line
containing string. If a parameter of zero is
given, the search is forward. String is
terminated by a "RETURN" or "NEW LINE". If string
is preceded by a ^, the matched line must begin
with string. If string is omitted, then the next
command line containing the most recent string is
accessed. In this case a parameter of zero
reverses the direction of the search.
^O Operate - Execute the current line and fetch the
next line relative to current line from the
history file.
M-digits (Escape) Define numeric parameter, the digits are
taken as a parameter to the next command. The
commands that accept a parameter are ^F, ^B,
erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-,
M-b, M-c, M-d, M-f, M-h M-l and M-^H.
M-letter Soft-key - Your alias list is searched for an
alias by the name letter and if an alias of this
name is defined, its value will be inserted on the
input queue. The letter must not be one of the
above meta-functions. M-]letter Soft-key - Your
alias list is searched for an alias by the name
letter and if an alias of this name is defined,
its value will be inserted on the input queue.
The can be used to program functions keys on many
terminals.
M-. The last word of the previous command is inserted
on the line. If preceded by a numeric parameter,
the value of this parameter determines which word
to insert rather than the last word.
M- Same as M-..
M-* Attempt file name generation on the current word.
An asterisk is appended if the word doesn't match
any file or contain any special pattern
characters.
M-ESC File name completion. Replaces the current word
with the longest common prefix of all filenames
matching the current word with an asterisk
appended. If the match is unique, a / is appended
if the file is a directory and a space is appended
if the file is not a directory.
M-= List files matching current word pattern if an
asterisk were appended.
^U Multiply parameter of next command by 4.
\ Escape next character. Editing characters, the
user's erase, kill and interrupt (normally ^?)
characters may be entered in a command line or in
a search string if preceded by a \. The \ removes
the next character's editing features (if any).
^V Display version of the shell.
M-# Insert a # at the beginning of the line and
execute it. This causes a comment to be inserted
in the history file.
Vi Editing Mode
There are two typing modes. Initially, when you enter a
command you are in the input mode. To edit, the user enters
control mode by typing ESC ( 033 ) and moves the cursor to
the point needing correction and then inserts or deletes
characters or words as needed. Most control commands accept
an optional repeat count prior to the command.
When in vi mode on most systems, canonical processing is
initially enabled and the command will be echoed again if
the speed is 1200 baud or greater and it contains any
control characters or less than one second has elapsed since
the prompt was printed. The ESC character terminates
canonical processing for the remainder of the command and
the user can then modify the command line. This scheme has
the advantages of canonical processing with the type-ahead
echoing of raw mode.
If the option viraw is also set, the terminal will always
have canonical processing disabled. This mode is implicit
for systems that do not support two alternate end of line
delimiters, and may be helpful for certain terminals.
Input Edit Commands
By default the editor is in input mode.
erase (User defined erase character as defined by
the stty command, usually ^H or #.) Delete
previous character.
^W Delete the previous blank separated word.
^D Terminate the shell.
^V Escape next character. Editing characters,
the user's erase or kill characters may be
entered in a command line or in a search
string if preceded by a ^V. The ^V removes
the next character's editing features (if
any).
\ Escape the next erase or kill character.
Motion Edit Commands
These commands will move the cursor.
[count]l Cursor forward (right) one character.
[count]w Cursor forward one alpha-numeric word.
[count]W Cursor to the beginning of the next word that
follows a blank.
[count]e Cursor to end of word.
[count]E Cursor to end of the current blank delimited
word.
[count]h Cursor backward (left) one character.
[count]b Cursor backward one word.
[count]B Cursor to preceding blank separated word.
[count]| Cursor to column count.
[count]fc Find the next character c in the current
line.
[count]Fc Find the previous character c in the current
line.
[count]tc Equivalent to f followed by h.
[count]Tc Equivalent to F followed by l.
[count]; Repeats count times, the last single
character find command, f, F, t, or T.
[count], Reverses the last single character find
command count times.
0 Cursor to start of line.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is
entered the previous command back in time is
accessed.
[count]- Equivalent to k.
[count]j Fetch next command. Each time j is entered
the next command forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The
default is the least recent history command.
/string Search backward through history for a
previous command containing string. String
is terminated by a "RETURN" or "NEW LINE".
If string is preceded by a ^, the matched
line must begin with string. If string is
null the previous string will be used.
?string Same as / except that search will be in the
forward direction.
n Search for next match of the last pattern to
/ or ? commands.
N Search for next match of the last pattern to
/ or ?, but in reverse direction. Search
history for the string entered by the
previous / command.
Text Modification Edit Commands
These commands will modify the line.
a Enter input mode and enter text after the
current character.
A Append text to the end of the line.
Equivalent to $a.
[count]cmotion
c[count]motion
Delete current character through the
character that motion would move the cursor
to and enter input mode. If motion is c, the
entire line will be deleted and input mode
entered.
C Delete the current character through the end
of line and enter input mode. Equivalent to
c$.
S Equivalent to cc.
D Delete the current character through the end
of line. Equivalent to d$.
[count]dmotion
d[count]motion
Delete current character through the
character that motion would move to. If
motion is d , the entire line will be
deleted.
i Enter input mode and insert text before the
current character.
I Insert text before the beginning of the line.
Equivalent to 0i.
[count]P Place the previous text modification before
the cursor.
[count]p Place the previous text modification after
the cursor.
R Enter input mode and replace characters on
the screen with characters you type overlay
fashion.
[count]rc Replace the count character(s) starting at
the current cursor position with c, and
advance the cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification
command.
[count]~ Invert the case of the count character(s)
starting at the current cursor position and
advance the cursor.
[count] Causes the count word of the previous command
to be appended and input mode entered. The
last word is used if count is omitted.
* Causes an * to be appended to the current
word and file name generation attempted. If
no match is found, it rings the bell.
Otherwise, the word is replaced by the
matching pattern and input mode is entered.
\ Filename completion. Replaces the current
word with the longest common prefix of all
filenames matching the current word with an
asterisk appended. If the match is unique, a
/ is appended if the file is a directory and
a space is appended if the file is not a
directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that
motion would move the cursor to and puts them
into the delete buffer. The text and cursor
are unchanged.
Y Yanks from current position to end of line.
Equivalent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands
performed on 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. Parameter assignment lists preceding the command remain
in effect when the command completes.
2. I/O redirections are processed after parameter
assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by †† that are in
the format of a parameter assignment, are expanded with
the same rules as a parameter assignment. This means
that tilde substitution is performed after the = sign
and word splitting and file name 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 remained tracked. Without the -t flag,
for each name in the argument list for which no value
is given, the name and value of the alias is printed.
The -x flag is used to set or print exported aliases.
An exported alias is defined for scripts invoked by
name. The exit status is non-zero if a name is given,
but no value, for which no alias has been defined.
bg [ job... ]
This command is only on systems that support job
control. Puts each specified job into the background.
The current job is put in the background if job is not
specified. See Jobs for a description of the format of
job.
† break [ n ]
Exit from the enclosing for while until or select loop,
if any. If n is specified then break n levels.
† continue [ n ]
Resume the next iteration of the enclosing for while
until or select loop. If n is specified then resume at
the n-th 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 parameter HOME is the default
arg. The parameter PWD is set to the current
directory. The shell parameter CDPATH defines the
search path for the directory containing arg.
Alternative directory names are separated by a
colon (:). The default path is <null> (specifying the
current directory). Note that the current directory is
specified by a null path name, which can appear
immediately after the equal sign or between the colon
delimiters anywhere else in the path list. If arg
begins with a / then the search path is not used.
Otherwise, each directory in the path is searched for
arg.
The second form of cd substitutes the string new for the
string old in the current directory name, PWD and tries to
change to this new directory.
The cd command may not be executed by rksh.
echo [ arg ... ]
See echo(C) 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 parameter FCEDIT (default /bin/ed) is used as the
editor. When editing is complete, the edited
command(s) is executed. If last is not specified then
it will be set to first. If first is not specified the
default is the previous command for editing and -16 for
listing. The flag -r reverses the order of the
commands and the flag -n suppresses command numbers
when listing. In the second form the command is re-
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.
let arg ...
Each arg is a separate arithmetic expression to be
evaluated. See Arithmetic Evaluation above, for a
description of arithmetic expression evaluation.
The exit status is 0 if the value of the last
expression is non-zero, and 1 otherwise.
† newgrp [ arg ... ]
Equivalent to exec /bin/newgrp arg ....
print [ -Rnprsu[n ] ] [ arg ... ]
The shell output mechanism. With no flags or with flag
- or -- the arguments are printed on standard output as
described by echo(C). 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.
† return [ n ]
Causes a shell function to return to the invoking
script with the return status specified by n. If n is
omitted then the return status is that of the last
command executed. If return is invoked while not in a
function or a script, then it is the same as an exit.
set [ +aefhkmnopstuvx ] [ +o option ]... [ +A name ] [ arg ... ]
The flags for this command have meaning as follows:
-A Array assignment. Unset the variable name and
assign values sequentially from the list arg.
If +A is used, the variable name is not unset
first.
-a All subsequent parameters that are defined are
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 parameter assignment arguments are placed
in the environment for a command, not just
those that precede the command name.
-m Background jobs will run in a separate process
group and a line will print upon completion.
The exit status of background jobs is reported
in a completion message. On systems with job
control, this flag is turned on automatically
for interactive shells.
-n Read commands and check them for syntax errors,
but do not execute them. Ignored for
interactive shells.
-o The following argument can be one of the
following option names:
allexport
Same as -a.
errexit Same as -e.
bgnice All background jobs are run at a lower
priority. This is the default mode.
emacs Puts you in an emacs style in-line
editor for command entry.
gmacs Puts you in a gmacs style in-line
editor for command entry.
ignoreeof
The shell will not exit on end-of-file.
The command exit must be used.
keyword Same as -k.
markdirs
All directory names resulting from file
name generation have a trailing /
appended.
monitor Same as -m.
noclobber
Prevents redirection > from truncating
existing files. Require >| to truncate
a file when turned on.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in
history file.
nounset Same as -u.
privileged
Same as -p.
verbose Same as -v.
trackall
Same as -h.
vi Puts you in insert mode of a vi style
in-line editor until you hit escape
character 033. This puts you in move
mode. A return sends the line.
viraw Each character is processed as it is
typed in vi mode.
xtrace Same as -x.
option settings are printed.
If no option name is supplied then the current
-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 named parameters
are printed on the standard output. If the only argument
is +, the names of all named parameters are printed.
† shift [ n ]
The positional parameters from $n+1 ... are renamed 1 ...,
default n is 1. The parameter n can be any arithmetic
expression that evaluates to a non-negative number less than
or equal to $#.
† times
Print the accumulated user and system times for the shell
and for processes run from the shell.
† trap [ arg ] [ sig ] ...
arg is a command to be read and executed when the shell
receives signal(s) sig. (Note that arg is scanned once when
the trap is set and once when the trap is taken.) Each sig
can be given as a number or as the name of the signal. Trap
commands are executed in order of signal number. Any
attempt to set a trap on a signal that was ignored on entry
to the current shell is ineffective. If arg is omitted or
is -, then all trap(s) sig are reset to their original
values. If arg is the null string then this signal is
ignored by the shell and by the commands it invokes. If sig
is ERR then arg will be executed whenever a command has a
non-zero exit status. sig is DEBUG then arg will be
executed after each command. If sig is 0 or EXIT and the
trap statement is executed inside the body of a function,
then the command arg is executed after the function
completes. If sig is 0 or EXIT for a trap set outside any
function then the command arg is executed on exit from the
shell. The trap command with no arguments prints a list of
commands associated with each signal number.
†† typeset [ +HLRZfilrtux[n] ] [ name[ =value ] ] ...
Sets attributes and values for shell parameters. When
invoked inside a function, a new instance of the parameter
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 system to host-name file
mapping on non-UNIX system machines.
-L Left justify and remove leading blanks from value. If
n is non-zero it defines the width of the field,
otherwise it is determined by the width of the value of
first assignment. When the parameter is assigned to,
it is filled on the right with blanks or truncated, if
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 parameter is reassigned.
The L flag is turned off.
-Z Right justify and fill with leading zeros if the first
non-blank character is a digit and the -L flag has not
been set. If n is non-zero it defines the width of the
field, otherwise it is determined by the width of the
value of first assignment.
-f The names refer to function names rather than parameter
names. No assignments can be made and the only other
valid flags are -t, -u and -x. The flag -t turns on
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 Parameter is an integer. This makes arithmetic faster.
If n is non-zero it defines the output arithmetic base,
otherwise the first assignment determines the output
base.
-l All upper-case characters converted to lower-case. The
upper-case flag, -u is turned off.
-r The given names are marked readonly and these names
cannot be changed by subsequent assignment.
-t Tags the named parameters. Tags are user definable and
have no special meaning to the shell.
-u All lower-case characters are converted to upper-case
characters. The lower-case flag, -l is turned off.
-x The given names are marked for automatic export to the
environment of subsequently-executed commands.
Using + rather than - causes these flags to be turned off.
If no name arguments are given but flags are specified, a
list of names (and optionally the values) of the parameters
which have these flags set is printed. (Using + rather than
- keeps the values from being printed.) If no names and
flags are given, the names and attributes of all parameters
are printed.
ulimit [ -HS ] [ limit ]
The number of 512-byte blocks on files written by child
processes (files of any size may be read). The limit is set
when limit is specifed. The value of limit can be a number
or the value unlimited. The H and S flags specify whether
the hard limit or the soft limit is set. A hard limit
cannot be increased once it is set. A soft limit can be
increased up to the value of the hard limit. If neither the
H or S options is specified, the limit applies to both. The
current limit is printed when limit is omitted. In this
case the soft limit is printed unless H is specified.
umask [ mask ]
The user file-creation mask is set to mask (see umask(C)).
mask can either be an octal number or a symbolic value as
described in chmod(C). 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 parameters given by the list of names are removed from
the alias list.
unset [ -f ] name ...
The parameters given by the list of names are unassigned,
i.e., their values and attributes are erased. Readonly
variables 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.
The flag, -v, produces a more verbose report.
The flag, -p, does a path search for name even if name is an
alias, a function, or a reserved word.
Invocation.
If the shell is invoked by exec(S), 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 parameter ENV
if the file exists. If the -s flag is not present and arg
is, then a path search is performed on the first arg to
determine the name of the script to execute. The script arg
must have read permission and any setuid and getgid settings
will be ignored. Commands are then read as described below;
the 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(S)) 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 ksh, except that the following are
disallowed:
changing directory (see cd(C)),
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. Some systems also provide a restricted editor red.
Diagnostics
Errors detected by the shell, such as syntax errors, cause
the shell to return a non-zero exit status. Otherwise, the
shell returns the exit status of the last command executed
(see also the exit command above). If the shell is being
used non-interactively then execution of the shell file is
abandoned. Run time errors detected by the shell are
reported by printing the command or function name and the
error condition. If the line number that the error occurred
on is greater than one, then the line number is also printed
in square brackets ([]) after the command or function name.
Files
/etc/passwd
/etc/profile
/etc/suid_profile
$HOME/.profile
/tmp/sh*
/dev/null
See Also
cat(C), cd(C), chmod(C), cut(C), echo(C), env(C), newgrp(C),
stty(C), test(C), umask(C), vi(C), dup(S), exec(S), fork(S),
ioctl(S), lseek(S), paste(C), pipe(S), signal(S), umask(S),
ulimit(S), wait(S), rand(S), a.out(F), profile(M),
environ(M).
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 forground job terminates.
(printed 7/10/90) KSH(C)