ksh(1) ksh(1)
NAME
ksh - shell, the standard command programming language
SYNOPSIS
ksh [-a] [-e] [-f] [-h] [-i] [-k] [-m] [-n] [-o] [-p] [-r]
[-s] [-t] [-u] [-v] [-x] [-o flag_option]... [-c string]
[arg...]
rsh [ [-a] [-e] [-f] [-h] [-i] [-k] [-m] [-n] [-o] [-p] [-r]
[-s] [-t] [-u] [-v] [-x] [-o flag_option]... [-c string]
[arg...]
DESCRIPTION
ksh is a command programming language that executes commands
read from a terminal or a file. See ``Invocation'' below
for the meaning of arguments to the shell.
Definitions
A metacharacter is one of the following characters:
; & ( ) | < > newline space TAB
A blank is a TAB or a space. An identifier is a sequence of
letters, digits, or underscores starting with a letter or
underscore. Identifiers are used as names for aliases,
functions, and named parameters. A word is a sequence of
characters separated by one or more non-quoted
metacharacters.
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(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(3) 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 ||. The symbols && and
|| also have equal precedence. A semicolon (;) causes
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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 flag option of the special commands read and
print described later. Only one such command can be active
at any given time. The symbol && (||) causes the list
following it to be executed only if the preceding pipeline
returns a zero (non-zero) value. An arbitrary number of
newlines may appear in a list, instead of semicolons, to
delimit commands.
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
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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. A parenthesized list used as a
command argument denotes ``process substitution'' as
described below.
{ list;}
list is simply executed. Note that { is a keyword and
requires a blank in order to be recognized.
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 keywords are only recognized as the first word
of a command and when not quoted:
if then else elif fi case esac for while until do done { }
function select time
Comments
A word beginning with # causes that word and all the
following characters up to a newline to be ignored.
Aliasing
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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 of the
replaced text will not be tested for additional 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
built-in commands but cannot be used to redefine the
keywords 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
sub-shells 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 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 flag 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 flag
option of the set command makes each command name which is a
valid alias name into a tracked alias.
The following ``exported aliases'' are compiled into the
shell but can be unset or redefined:
false='let 0'
functions='typeset -f'
history='fc -l'
integer='typeset -i'
nohup='nohup '
r='fc -e -'
true=':'
type='whence -v'
hash='alias -t'
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
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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 the
value of the parameter PWD and OLDPWD respectively.
In addition, the value of each keyword parameter is checked
to see if it begins with a or if a appears after a :. In
either of these cases a tilde substitution is attempted.
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 newlines
are removed. In the second (archaic) form, the string
between the quotes is processed for special quoting
characters before the command is executed. (See ``Quoting''
below). The command substitution $(cat file) can be
replaced by the equivalent but faster $(<file). Command
substitution of most special commands that do not perform
input/output redirection are carried out without creating a
separate process.
Process Substitution.
This feature is only available on versions of the Oreog
operating system that support the /dev/fd directory for
naming open files. Each command argument of the form
(list), <(list), or >(list) will run process list
asynchronously connected to some file in /dev/fd. The name
of this file will become the argument to the command. If
the form with > is selected then writing on this file will
provide input for list. If < is used or omitted, then the
file passed as an argument will contain the output of the
list process. For example,
paste (cut -f1 file1) (cut -fC file2) | tee
>(process1) >(process2)
cuts fields 1 and 3 from the files file1 and file2
respectively, pastes the results together, and sends it to
the processes process1 and process2, as well as putting it
onto the standard output. Note that the file, which is
passed as an argument to the command, is an Oreo pipe(2) so
programs that expect to lseek(2) on the file will not work.
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
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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 sub-shells but only values to the
environment.
The shell supports a limited 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 ]. The value of all subscripts must be in the
range of 0 through 511. 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 first element.
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 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.
${#identifier[*]}
The number of elements in the array identifier is
substituted.
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${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 latter 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 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 latter 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.
The last argument of the previous command. This
parameter is not set for commands which are
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asynchronous. This parameter is also used to hold
the name of the matching MAIL file when checking
for mail. Finally, the value of this parameter is
set to the full path name of each program the
shell invokes and is passed in the environment.
! The process number of the last background command
invoked.
PPID The process number of the parent of the shell.
PWD The present working directory set by the cd
command.
OLDPWD
The previous working directory set by the cd
command.
RANDOM
Each time this parameter is referenced, a random
integer 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 vi and the
VISUAL variable is not set, then the corresponding
flag 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.
IFS Internal field separators, normally space, tab,
and newline that is used to separate command words
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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 and command 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 rsh (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
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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 #? .
SHELL
The pathname of the shell is kept in the
environment. At invocation, if the value of this
variable contains an r in the basename, 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, while HOME, SHELL ENV and MAIL are not set
at all by the shell (although HOME is set by login(1)). On
some systems MAIL and SHELL are also set by login(1)).
Blank Interpretation
After parameter and command substitution, the results of
substitutions are scanned for the field separator characters
( those found in IFS ) and split into distinct arguments
where such characters are found. Explicit null arguments
("" or '') 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 alphabetically 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
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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.
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 \newline 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 keywords or aliases can be removed by
quoting any character of the keyword. 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 internal integer representation of a named parameter can
be specified with the -i option of the typeset special
command. When this attribute is selected the first
assignment to the parameter determines the arithmetic base
to be 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
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PS1 before reading a command. If at any time a newline is
typed and further input is needed to complete a command,
then the secondary prompt (i.e., the value of PS2) is
issued.
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; otherwise, it is truncated
to zero length.
>>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 The shell input is read up to a line that is
the same as word, or to an end-of-file. No
parameter substitution, command substitution
or file name generation is performed on word.
The resulting document, called a ``here-
document'', becomes the standard input. If
any character of word is quoted, then no
interpretation is placed upon the characters
of the document; otherwise, parameter and
command substitution occurs, \newline is
ignored, and \ must be used to quote the
characters \, $, `, and the first character of
word. If - is appended to <<, then all
leading tabs are stripped from word and from
the document.
<&digit The standard input is duplicated from file
descriptor digit (see dup(2)). Similarly for
the standard output using >& digit.
<&- The standard input is closed. Similarly for
the standard output using >&-.
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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(7)) is a list of name-value
pairs that is passed to an executed program in the same way
as a normal argument list. The names must be identifiers
and the values are character strings. The shell interacts
with the environment in several ways. On invocation, the
shell scans the environment and creates a parameter for each
name found, giving it the corresponding value and marking it
export. Executed commands inherit the environment. If the
user 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:
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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
Functions
The function keyword, 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, traps ( other than EXIT and ERR) and
present working directory with the caller. A trap set on
EXIT inside a function is executed after the function
completes. 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 option of the
typeset special command. The text of functions will also be
listed. 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 placed in the ENV file.
Jobs
If the monitor option of the set command is turned on, an
interactive shell associates a job with each pipeline. It
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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.
This paragraph and the next require features that are not in
all versions of UNIX® and may not apply. 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.
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. The
character % introduces a job name. If you wish to refer to
job number 1, you can name it as %1 . Jobs can also be named
by prefixes of the string typed in to start them. Thus, on
systems that support job control, `fg %ed' would normally
restart a suspended ed(1) job, if there were a suspended job
whose name began with the string `ed'.
The shell maintains a notion of the current and previous
jobs. In output pertaining to jobs, the current job is
marked with a + and the previous job with a -. The
abbreviation %+ refers to the current job and %- refers to
the previous job. %% is also a synonym for the current 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 you try to leave the shell while jobs are running or
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stopped, you will be warned that `You have stopped (running)
jobs'. You may use the jobs command to see what they are.
If you do this or immediately try to exit again, the shell
will not warn you a second time, and the stopped jobs will
be terminated.
Signals
The INT and QUIT signals for an invoked command are ignored
if the command is followed by & and job monitor option is
not active. Otherwise, signals have the values inherited by
the shell from its parent (but see also the trap command
below).
Execution
Each time a command is executed, the above substitutions are
carried out. If the command name matches one of the
``Special Commands'' listed below, it is executed within the
current shell process. Next, the command name is checked to
see if it matches one of the user defined functions. If it
does, the positional parameters are saved and then reset to
the arguments of the function call. When the function
completes or issues a RETURN, the positional parameter list
is restored and any trap set on EXIT within the function is
executed. The value of a function is the value of the last
command executed. A function is also executed in the
current shell process. If a command name is not a special
command or a user defined function, a process is created and
an attempt is made to execute the command via exec(2).
The shell 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 also executed in a sub-
shell without removing non-exported quantities.
Command Re-entry
The text of the last HISTSIZE (default 128) commands entered
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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 newline (`RETURN' or
`LINE FEED'). If the 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.
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
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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 than 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]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.
; Repeats the last single character find
command, f, F, t, or T.
, Reverses the last single character find
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command.
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 NEWLINE. 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$.
[count]dmotion
d[count]motion
Delete current character through the
character that motion would move to. If
motion is d , the entire line will be
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deleted.
i Enter input mode and insert text before the
current character.
I Insert text before the beginning of the line.
Equivalent to the two character sequence ^i.
[count]P Place the previous text modification before
the cursor.
[count]p Place the previous text modification after
the cursor.
R Enter input mode and replace characters on
the screen with characters you type overlay
fashion.
rc Replace the current character with c.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification
command.
Invert the case of the current character and
advance the cursor.
[count]_ Causes the count word of the previous command
to be appended and input mode entered. The
last word is used if count is omitted.
* Causes an * to be appended to the current
word and file name generation attempted. If
no match is found, it rings the bell.
Otherwise, the word is replaced by the
matching pattern and input mode is entered.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that
motion would move the cursor to and puts them
into the delete buffer. The text and cursor
are unchanged.
Y Yanks from current position to end of line.
Equivalent to y$.
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 and after each newline. Useful
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for causing the current line to be inserted
in the history without being executed.
= List the filenames 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. 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. They are executed in a separate process when used
within command substitution.
3. Errors in commands preceded by †† cause the script that
contains them to abort.
† : arg ... ]
The command only expands parameters. A zero exit code
is returned.
†† . file arg ... ]
Read and execute commands from file and return. 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.
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 across sub-shell
environments. Alias returns true unless a name is
given for which no alias has been defined.
bg %job ]
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This command is only built-in on systems that support
job control. Puts the specified job into the
background. The current job is put in the background
if job is not specified.
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 rsh.
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
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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 ... ]
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 built-in on systems that support
job control. If job is specified it brings it to the
foreground. Otherwise, the current job is brought into
the foreground.
jobs -l ]
Lists the active jobs; given the -l options lists
process id's in addition to the normal information.
kill -sig ] process ...
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
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SIG). The signal numbers and names are listed by kill
-l. 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
process can be either a process ID or a job.
let arg ...
Each arg is an arithmetic expression to be evaluated.
All calculations are done as long integers and no check
for overflow is performed. Expressions consist of
constants, named parameters, and operators. The
following set of operators, listed in order of
decreasing precedence, have been implemented:
- unary minus
! logical negation
* / %
multiplication, division, remainder
+ - addition, subtraction
<= >= < >
comparison
== !=
equality inequality
= arithmetic replacement
Sub-expressions in parentheses () are evaluated first
and can be used to override the above precedence rules.
The evaluation within a precedence group is from right
to left for the = operator and from left to right for
the others.
A parameter name must be a valid identifier. When a
parameter is encountered, the value associated with the
parameter name is substituted and expression evaluation
resumes. Up to nine levels of recursion are permitted.
The return code is 0 if the value of the last
expression is non-zero, and 1 otherwise.
†† newgrp arg ... ]
Equivalent to exec newgrp arg ....
print -Rnprsun ] ] arg ... ]
The shell output mechanism. With no flags or with flag
-, 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 option can be used to
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specify a one digit file descriptor unit number n on
which the output will be placed. The default is 1. If
the flag option -n is used, no newline is added to the
output.
pwd Equivalent to print -r - $PWD
read -prsu n ] ] name?prompt ] name ... ]
The shell input mechanism. One line is read and is
broken up into words 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 word is
assigned to the first name, the second word to the
second name, etc., with leftover words 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 return code 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 when the
shell is interactive. If the given file descriptor is
open for writing and is a terminal device then the
prompt is placed on this unit. Otherwise the prompt is
issued on file descriptor 2. The return code is 0
unless an end-of-file is encountered.
†† readonly name ... ]
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 -aefhkmnostuvx ] -o option ... ] arg ... ]
The flags for this command have meaning as follows:
-a All subsequent parameters that are defined are
automatically exported.
-e If the shell is non-interactive and if a
command fails, execute the ERR trap, if set,
and exit immediately. This mode is disabled
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while reading profiles.
-f Disables file name generation.
-h Each command whose name is an identifier
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 but do not execute them. Ignored
for interactive shells.
-o The following argument can be one of the
following names:
allexport Same as -a.
errexit Same as -e.
bgnice All background jobs are run at a
lower priority.
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.
noexec Same as -n.
noglob Same as -f.
nounset Same as -u.
protected Same as -p.
verbose Same as -v.
trackall Same as -h.
vi Puts you in insert mode of a vi
style in-line editor until you
hit escape character 033. This
puts you in move mode. A return
sends the line.
viraw Each character is processed as
it is typed in vi mode.
xtrace Same as -x.
If no flag option name is supplied then the current
settings are printed.
-p Resets the PATH variable to the default value,
disables processing of the $HOME/.profile file
and uses the file /etc/suidprofile instead of
the ENV file. This mode is automatically
enabled whenever the effective uid (gid) is not
equal to the real uid (gid).
-s Sort the positional parameters.
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-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
$-. The remaining arguments are positional parameters
and are assigned, in order, to $1 $2 .... If no
arguments are given then the values of all names 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 $#.
test expr ]
Evaluate conditional expression expr. See test(1) for
usage and description. The arithmetic comparison
operators are not restricted to integers. They allow
any arithmetic expression. Four additional primitive
expressions are allowed:
-L file True if file is a symbolic link.
file1 -nt file2 True if file1 is newer than file2.
file1 -ot file2 True if file1 is older than file2.
file1 -ef file2 True if file1 has the same device
and i-node number as file2.
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
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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
code. This trap is not inherited by functions. 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 -HLRZfilprtuxn ] name =value ] ] ... ]
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 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 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, which turns on
execution tracing for this function and -x, to
allow the function to remain in effect across
shell procedures executed in the same process
environment.
-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.
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-l All upper-case characters converted to lower-case.
The upper-case flag, -u is turned off.
-p The output of this command, if any, is written
onto the two-way pipe
-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 to be
printed.) If no names and flags are given, the names
and attributes of all parameters are printed.
ulimit -acdfmpst ] n ]
-a Lists all of the current resource limits (BSD
only).
-c imposes a size limit of n 512 byte blocks on the
size of core dumps (BSD only).
-d imposes a size limit of n kbytes on the size of
the data area (BSD only).
-f imposes a size limit of n 512 byte blocks on files
written by child processes (files of any size may
be read).
-m imposes a soft limit of n kbytes on the size of
physical memory (BSD only).
-p changes the pipe size to n (UNIX/RT only).
-s imposes a size limit of n kbytes on the size of
the stack area (BSD only).
-t imposes a time limit of n seconds to be used by
each process (BSD only).
If no option is given, -f is assumed. If n is not
given the current limit is printed.
umask nnn ]
The user file-creation mask is set to nnn (see
umask(2)). If nnn 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.
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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.
wait n ]
Wait for the specified child process and report its
termination status. If n is not given then all
currently active child processes are waited for. The
return code from this command is that of the process
waited for.
whence -v ] name ...
For each name, indicate how it would be interpreted if
used as a command name.
The flag, -v, produces a more verbose report.
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 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(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.
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The remaining flags and arguments are described under the
set command above.
rsh Only.
rsh is used to set up login names and execution environments
whose capabilities are more controlled than those of the
standard shell. The actions of rsh are identical to those
of ksh, except that the following are disallowed:
changing directory (see cd(1)),
setting the value of SHELL, ENV, or PATH,
specifying path or command names containing /,
redirecting output (> and >>).
The restrictions above are enforced after .profile and the
ENV files are interpreted.
When a command to be executed is found to be a shell
procedure, rsh 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
rsh. Some systems also provide a restricted editor red.
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. Runtime 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
/bin/ksh
/etc/passwd
/etc/profile
/etc/suidprofile
$HOME/.profile
/tmp/ksh*
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/dev/null
SEE ALSO
cat(1), cd(1), echo(1), env(1), newgrp(1), test(1),
umask(1), vi(1), dup(2), exec(2), fork(2), ioctl(2),
lseek(2), pipe(2), signal(3), umask(2), ulimit(2), wait(2),
rand(3), a.out(5), profile(5), environ(7).
``Korn shell reference'' in Oreo User Interface.
CAVEATS
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. |.
If a command is piped into a shell command, then all
variables set in the shell command are lost when the command
completes.
Using the fc built-in command within a compound command will
cause the whole command to disappear from the history file.
The built-in command . file reads the whole file before any
commands are executed. Therefore, alias and unalias
commands in the file will not apply to any functions defined
in the file.
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