ksh(1) CLIX ksh(1)
NAME
ksh, krsh - Runs standard/restricted Korn Shell command/programming
language
SYNOPSIS
ksh [+aefhikmnoprstuvx] [+o option] ... [-c string] [arg ...]
krsh [+aefhikmnoprstuvx] [+o option] ... [-c string] [arg ...]
DESCRIPTION
The ksh command runs the command interpreter for the Korn Shell, a command
and programming language that executes commands read from either a
terminal or a file. The krsh command runs a restricted version of ksh; it
us used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
See "Invocation" 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 an underscore. Identifiers are used as names for
functions and variables.
A word is a sequence of characters separated by one or more nonquoted
metacharacters.
A command is a sequence of characters in shell language syntax. The shell
reads each command and carries out the desired action, either directly or
by invoking separate utilities.
A special command is a command that is carried out by the shell without
creating a separate process. Except for documented side effects, most
special commands can be implemented as separate utilities.
Commands
A simple-command is a sequence of blank-separated words which may be
preceded by a variable assignment list (see "Environment"). The first
word specifies the name of the command to be executed. Except as
specified in the following text, the remaining words are passed as
arguments to the invoked command. The command name is passed as argument
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0 (see the exec() function). The value of a simple-command is its exit
status if it terminates normally, or (octal) 200+status if it terminates
abnormally (see the signal() function for a list of status values).
A pipeline is a sequence of one or more commands separated by |. The
stdout of each command that is terminated by a pipe() is used as stdin to
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 the following
symbols:
; Causes sequential execution of the preceding pipeline.
& Causes asynchronous execution of the preceding pipeline (that is,
the shell does not wait for that pipeline to finish).
&& Causes the list following it to be executed only if the preceding
pipeline returns a 0 value.
|| Causes the list following it to be executed only if the preceding
pipeline returns a nonzero value.
|& Causes asynchronous execution of the preceding command or pipeline
with a two-way pipe established to the parent shell. The stdin and
stdout 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).
A list is optionally terminated by ;, &, or |&. An arbitrary number of
newlines may appear in a list, instead of a semicolon, to delimit a
command. These five symbols have the following precedence, in descending
order:
&&
||
;, &, and |& (equal precedence)
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"). Execution
ends when there are no more words in the list.
select identifier [in word ... ] ; do list ; done
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A select command prints on stderr (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"). The PS3 prompt is printed and a line is read from
stdin. If this line consists of the number of one of the listed
words, then the value of the variable 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 variable
identifier is set to null. The contents of the line read from
stdin is saved in the variable REPLY. The list is executed for
each selection until a break or end-of-file is encountered. If the
REPLY variable is set to null by the execution of list, then the
selection list is printed before displaying the PS3 prompt for the
next selection.
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 filename generation (see "Filename Generation").
if list1 ; then list2 [elif list3 ; then list4] ... [ ; else list n] ; fi
The list1 argument is executed and, if it returns a 0 exit value,
list2 is executed. Otherwise, list3 is executed and, if its exit
value is 0, list4 then is executed. Failing that, list n is
executed. If no else list n or list4 is executed, the if command
returns a 0 exit value.
while list1 ; do list2 ; done
until list1 ; do list2 ; done
A while command repeatedly executes list1 and, if the exit value of
the last command in the list is 0, executes list2; otherwise the
loop terminates. The until command may be used in place of while
to negate the loop termination test. If no commands in list2 are
executed, the while and do commands return a 0 exit value.
(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 in the following text.
{ list ; }
The list is simply executed. Note that unlike the metacharacters (
and ), { and } are reserved words and must occur at the beginning
of a line or after a ; in order to be recognized.
[[ expression ]]
Evaluates expression and returns a 0 exit value if expression is
true. See "Conditional Expressions" for a description of
expression.
function identifier { list ; }
identifier () { list ; }
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Define a function which is referenced by identifier. The body of
the function is the list of commands between { and } (see
"Functions").
time pipeline
The pipeline is executed and the elapsed time as well as the user
and system time are printed on stderr.
The following reserved words are only recognized as the first word of a
command and when not quoted:
if then else elif fi case esac for while until do done
{ } function select time [[ ]]
Comments
A word beginning with # causes that word and all the following characters
up to a newline to be ignored.
Aliasing
The first word of each command is replaced by the text of an alias if an
alias for this word has been defined. An alias name consists of any
number of characters excluding metacharacters, quoting characters, file
expansion characters, parameter and command substitution characters, and
=. The replacement string can contain any valid shell script including
the metacharacters listed previously. 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 built-in commands, but cannot be
used to redefine the reserved words listed previously. 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").
Aliasing is performed when scripts are read, not while they are being
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.
An alias is frequently used as a shorthand reference for a full pathname.
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
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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 username in the /etc/passwd file. If a match is
found, the ~ and the matched login name are replaced by the login
directory of the matched user; this is called a tilde substitution. If no
match is found, the original text is left unchanged. A ~ by itself, or in
front of a /, is replaced by $HOME. A ~ followed by a + or - is replaced
by $PWD or $OLDPWD, respectively.
In addition, tilde substitution is attempted when the value of a variable
assignment begins with a ~.
Command Substitution
The stdout from a command enclosed in parentheses preceded by a dollar
sign -- $( ) -- or a pair of grave accents -- `` -- may be used as part or
all of a word; trailing 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"). The command
substitution $(cat file) can be replaced by the equivalent but faster
$(<file). Command substitution of most special commands that do not
perform input/output redirection are carried out without creating a
separate process.
An arithmetic expression enclosed in double parentheses preceded by a
dollar sign -- $(( )) -- is replaced by the value of the arithmetic
expression within the double parentheses.
Process Substitution
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This feature is only available on versions of the UNIX operating system
that support the /dev/fd directory for naming open files. Each command
argument of the form <(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, then
the file passed as an argument will contain the output of the list
process. Note the following example:
paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)
This command 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 stdout. Note that the
file, which is passed as an argument to the command, is a UNIX pipe;
programs that expect to perform an lseek command on the file will not
work.
Parameter Substitution
A parameter is an identifier, one or more digits, or any of the following
characters:
* @ L# ? $ ! -
A variable (a parameter denoted by an identifier) has a value and zero or
more attributes. Variables can be assigned values and attributes by using
the special command typeset. The attributes supported by the shell are
described later with the typeset special command. Exported variables pass
values and attributes to the environment.
The shell supports a one-dimensional array facility. An element of an
array variable is referenced by a subscript. A subscript is denoted by a
[, followed by an arithmetic expression (see "Arithmetic Evaluation")
followed by a ]. To assign values to an array, use set -A name value ...
. The value of all subscripts must be in the range of 0 through 1023.
Arrays need not be declared. Any reference to a variable with a valid
subscript is legal and an array will be created if necessary. Referencing
an array without a subscript is equivalent to referencing the first
element (element 0).
The value of a variable may 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 in the following text.
Positional parameters, parameters denoted by a number, may be assigned
values with the set special command. Parameter $0 is set from argument 0
when the shell is invoked.
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The character $ is used to introduce substitutable parameters.
${parameter}
The shell reads all the characters from ${ to the matching } as
part of the same word even if it contains braces or metacharacters.
The value, if any, of the parameter is substituted. The braces are
required when parameter is followed by a letter, digit, or
underscore that is not to be interpreted as part of its name or
when a variable is subscripted. If parameter is one or more
digits, it is a positional parameter. A positional parameter of
more than one digit must be enclosed in braces. If parameter is *
or @, all positional parameters, starting with $1, are substituted
(separated by a field separator character). If an array identifier
with subscript * or @ is used, 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 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 the following message is printed:
ksh: foo: parameter null or not set
${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
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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.
A 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 previously described 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 of underscore (_) 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.
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OPTIND The index of the last option argument processed by the getopts
special command.
PPID The process number of the parent of the shell.
PWD The present working directory set by the cd command.
RANDOM Each time this variable is referenced, a random integer, uniformly
distributed between 0 and 32767, is generated. The sequence of
random numbers can be initialized by assigning a numeric value to
RANDOM.
REPLY This variable is used to store input by the select statement and by
the read special command when no arguments are supplied.
SECONDS
Each time this variable is referenced, the number of seconds since
shell invocation is returned. If this variable is assigned a
value, then the value returned upon reference will be the value
that was assigned plus the number of seconds since the assignment.
The following variables are used by the shell:
CDPATH The search path for the cd command.
COLUMNS
If this variable is set, the value is used to define the width of
the edit window for the shell edit modes and for printing select
lists.
EDITOR If the value of this variable ends in emacs, gmacs, or vi and the
VISUAL variable is not set, then the corresponding option (see
"Special Commands," set) will be turned on.
ENV If this variable is set, then parameter substitution is performed
on the value to generate the pathname of the script that will be
executed when the shell is invoked (see "Invocation"). This file
is typically used for alias and function definitions.
FCEDIT The default editor name for the fc command.
FPATH The search path for function definitions. This path is searched
when a function with the -u attribute is referenced and when a
command is not found. If an executable file is found, then it is
read and executed in the current environment.
IFS Internal field separators, normally space, tab, and newline that
are used to separate command words which result from command or
parameter substitution and for separating words with the special
command read. The first character of the IFS variable is used to
separate arguments for the "$*" substitution (see "Quoting").
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HISTFILE
If this variable is set when the shell is invoked, then the value
is the pathname of the file that will be used to store the command
history (see "Command Re-entry"). This variable must be set before
the first function definition or the end of the environment file.
HISTSIZE
If this variable is set when the shell is invoked, then the number
of previously entered commands that are accessible by this shell
will be less than or equal to this number. The default value is
128 commands. This variable must be set before the first function
definition or the end of the environment file.
HOME The default argument (home directory) for the cd command.
LINES If this variable is set, the value is used to determine the column
length for printing select lists. Select lists will print
vertically until about two-thirds of LINES lines are filled.
MAIL If this variable is set to the name of a mail file and the MAILPATH
variable is not set, then the shell informs the user of arrival of
mail in the specified file.
MAILCHECK
This variable specifies how often (in seconds) the shell will check
for changes in the modification time of any of the files specified
by the MAILPATH or MAIL variables. The default value is 600
seconds. When the time has elapsed the shell will check before
issuing the next prompt.
MAILPATH
A colon-separated list of filenames. If this variable is set, then
the shell informs the user of any modifications to the specified
files that have occurred within the last MAILCHECK seconds. Each
filename can be followed by a ? and a message that will be printed.
The message will undergo parameter substitution with the variable
$_ defined as the name of the file that has changed. The default
message is the following:
you have mail in $_
PATH The search path for commands (see "Execution"). The user may not
change PATH if executing under krsh (except in .profile).
PS1 The value of this variable is expanded for parameter substitution
to define the primary prompt string which by default is $ . The
character ! in the primary prompt string is replaced by the command
number (see "Command Re-entry"). Two successive occurrences of !
will produce a single ! when the prompt string is printed.
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PS2 The secondary prompt string, > by default.
PS3 The prompt string used within a select loop, #? by default.
PS4 The value of this variable is expanded for parameter substitution
and precedes each line of an execution trace. If omitted, the
execution trace prompt is + .
SHELL The pathname of the shell is kept in the environment. At
invocation, if the basename of this variable matches the pattern
*r*sh, then the shell becomes restricted.
TMOUT If set to a value greater than 0, 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 will be turned on (see set under "Special
Commands").
The shell gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK,
FCEDIT, TMOUT and IFS, while HOME, SHELL ENV and MAIL are not set at all
by the shell (although HOME is set by login). On some systems, MAIL and
SHELL are also set by login.
Blank Interpretation
After parameter and command substitution, the results of substitutions are
scanned for the field separator characters (those found in IFS) and split
into distinct arguments where such characters are found. Explicit null
arguments ("" or '') are retained. Implicit null arguments (those
resulting from parameters that have no values) are removed.
Filename Generation
Following substitution, each command word is scanned for the characters *,
?, and [...] unless the -f option has been set. If one of these
characters appears, word is regarded as a pattern. The word is replaced
with lexicographically sorted filenames that match the pattern. If no
filename is found that matches the pattern, then the word is left
unchanged. When a pattern is used for filename generation, the character
. at the start of a filename 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
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separated by - matches any character lexically between the pair,
inclusive. If the first character following the opening [ is a !,
then any character not enclosed is matched. A - can be included
in the character set by putting it as the first or last character.
A pattern-list is a list of one or more patterns separated from each other
with a |. Composite patterns can be formed with one or more of the
following:
?(pattern-list)
Optionally matches any one of the given patterns.
*(pattern-list)
Matches zero or more occurrences of the given patterns.
+(pattern-list)
Matches one or more occurrences of the given patterns.
@(pattern-list)
Matches exactly one of the given patterns.
!(pattern-list)
Matches everything, except one of the given patterns.
Quoting
Each of the metacharacters listed previously (see "Definitions") has a
special meaning to the shell and causes termination of a word unless
quoted. A character may be quoted (that is, made to stand for itself) by
preceding it with a \. The pair \newline is removed. All characters
enclosed between a pair of single quotation marks ( '' ), are quoted. A
single quotation mark cannot appear within single quotation marks. Inside
double quotation marks (""), parameter and command substitution occur and
\ quotes the characters \, `, ", and $. The meaning of "$*" and "$@" is
identical when not quoted or when used as a parameter assignment value or
as a filename. However, when used as a command argument, "$*" is
equivalent to "$1d$2d ...", where d is the first character of the IFS
variable, whereas "$@" is equivalent to "$1" "$2" ... . Inside grave
quotation marks ( `` ), \ quotes the characters \, `, and $. If the grave
quotation marks occur within double quotation marks, 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 cannot be altered by quoting them.
Arithmetic Evaluation
The special command let provides the ability to perform integer
arithmetic. Evaluations are performed using long arithmetic. Constants
are of the form [base#]n, where base is a decimal number between 2 and 36
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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 as the C language. All the integral
operators, other than ++, --, ?:, and ,, are supported. Variables can be
referenced by name within an arithmetic expression without using the
parameter substitution syntax. When a variable is referenced, its value
is evaluated as an arithmetic expression.
An internal integer representation of a variable can be specified with the
-i option of the typeset special command. Arithmetic evaluation is
performed on the value of each assignment to a variable with the -i
attribute. If you do not specify an arithmetic base, the first assignment
to the variable determines the arithmetic base. This base is used when
parameter substitution occurs.
Since many of the arithmetic operators require quoting, an alternative
form of the let command is provided. For any command which begins with a
((, all the characters until a matching )) are treated as a quoted
expression. More precisely, (( ... )) is equivalent to let "...".
Prompting
When used interactively, the shell prompts with the parameter-expanded
value of PS1 before reading a command. If at any time a newline is typed
and further input is needed to complete a command, then the secondary
prompt (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 filename
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.
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-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 nonzero.
-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 0.
-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 0.
-L file
True if file exists and is a symbolic link.
-O file
True if file exists and is owned by the effective user ID of this
process.
-G file
True if file exists and its group matches the effective group ID of
this process.
-S file
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True if file exists and is a socket.
file1 -nt file2
True if file1 exists and is newer than file2.
file1 -ot file2
True if file1 exists and is older than file2.
file1 -ef file23
True if file1 and file2 exist and refer to the same file.
string = pattern
True if string matches pattern.
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 these expressions, if file is of the form /dev/fd/n, where n is
an integer, then the test is applied to the open file whose descriptor
number is n.
A compound expression can be constructed from these primitives by using
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any of the following, listed in descending 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 or both are true.
Input/Output
Standard input (stdin) for the shell is defined as the input from the
keyboard; standard output (stdout) is defined as messages displayed to the
screen; and standard error (stderr) is defined as error messages displayed
to the screen. 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. They are not passed on to the invoked command. Command
and parameter substitution occur before word or digit is used, except as
noted in the following text. Filename generation occurs only if the
pattern matches a single file, and blank interpretation is not performed.
< word Use file word as stdin (file descriptor 0).
> word Use file word as stdout (file descriptor 1). If the file does not
exist, 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
Same as >, except that it overrides the noclobber option.
>> word
Use file word as stdout. If the file exists, 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 stdin.
<<[-]word
The shell input is read up to a line that is the same as word, or
to an end-of-file. Parameter substitution, command substitution,
and filename generation are not performed on word. The resulting
document, called a here-document, becomes stdin. If any character
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of word is quoted, then no interpretation is placed upon the
characters of the document; otherwise, parameter and command
substitution occur, \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 stdin is duplicated from file descriptor digit (see the dup()
function); similarly for stdout using >& digit.
<&- The stdin is closed; similarly for the stdout using >&-.
<&p The input from the coprocess is moved to stdin.
>&p The output to the coprocess is moved to stdout.
If one of these 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
This opens file descriptor 2 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
This associates file descriptor 1 with file fname. It then associates
file descriptor 2 with the file associated with file descriptor 1 (that is
fname). If the order of redirections were reversed, file descriptor 2
would be associated with the terminal (assuming file descriptor 1 had
been) and then file descriptor 1 would be associated with file fname.
If a command is followed by & and job control is not active, then the
default stdin 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(4)) is a list of name-value pairs that is
passed to an executed program in the same way as a normal argument list.
The names must be identifiers and the values are character strings.
The shell interacts with the environment in several ways. On invocation,
the shell scans the environment and creates a variable for each name
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found, giving it the corresponding value and marking it export. Executed
commands inherit the environment. If the user modifies the values of
these variables or creates new ones, using the export or typeset -x
commands, they become part of the environment. The environment seen by
any executed command is thus composed of any name-value pairs originally
inherited by the shell, whose values may be modified by the current shell,
plus any additions which must be noted in the export or typeset -x
commands.
The environment for any simple-command or function may be augmented by
prefixing it with one or more variable assignments. A variable assignment
argument is a word of the form identifier=value. Thus, the following
commands are equivalent (as far as the execution of cmd is concerned,
except for special commands that are preceded with a dagger):
TERM=450 cmd args
(export TERM; TERM=450; cmd args)
If the -k flag is set, all variable assignment arguments are placed in the
environment, even if they occur after the command name. The following
first prints a=b c and then c:
echo a=b c
set -k
echo a=b c
This feature is intended for use with scripts written for early versions
of ksh and its use in new scripts is strongly discouraged. It is likely
to be removed in a future release of ksh.
Functions
The function reserved word (see "Commands") 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. The value
of a function is the value of the last command executed (see "Execution").
Functions execute in the same process as the caller and share all files
and the current 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.
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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.
Functions 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 the following:
[1] 1234
indicating that the job which was started asynchronously was job 1 and had
one (top-level) process whose process ID was 1234.
If you are running a job and wish to do something else, keying in ^Z (the
<Ctrl-Z> sequence) sends a STOP signal to the current job (see the
signal() function). The shell will then normally indicate that the job
has been stopped and will 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
similar to 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.
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%+ Equivalent to %%.
%- Previous job.
The 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 or 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 and
running jobs will be terminated.
Signals
The INT and QUIT signals for an invoked command are ignored if the command
is followed by & and the monitor option is not active. Otherwise, signals
have the values inherited by the shell from its parent (but see also
information on the trap special command).
Execution
Each time a command is executed, the previously described substitutions
are carried out. If the command name matches one of the special commands,
it is executed within the current shell process (see "Special Commands").
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 with the exec() function (see exec()).
The shell variable PATH defines the search path for the directory
containing the command. Alternative directory names are separated by a
colon. The default path is the following:
/bin:/usr/bin:.
This path specifies /bin, /usr/bin, and the current directory in that
order. If the command name contains a /, then the search path is not
used. The current directory can be specified by two or more adjacent
colons, a dot (.) between two colons, or by two colons at the beginning or
end of the path list. Otherwise, each directory in the path is searched
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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 nonexported aliases,
functions, and variables are removed in this case. If the shell command
file does not have read permission, or if the setuid and/or setgid bits
(see ls(1)) 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 nonexported quantities.
Command Re-entry
The text of the last HISTSIZE commands (the default vaule is 128) entered
from a terminal device is saved in a history file. The file
$HOME/.sh_history is used if the HISTFILE variable is not set or if the
file it names is not writable. A shell can access the commands of all
interactive shells which use the same named HISTFILE.
The special command fc is used to list or edit a portion of this file.
The portion of the file to be edited or listed can be selected by number
or by giving the first character or characters of the command. A single
command or range of commands can be specified. If you do not specify an
editor program as an argument to fc, then the value of the variable FCEDIT
is used. If FCEDIT is not defined, then /bin/ed is used.
Edited commands are 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.
Inline Editing Options
Normally, each command line entered from a terminal device is keyed in and
followed by pressing <Return> or <Line Feed>. If 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 linefeed and that a space must overwrite the
current character on the screen.
The editing modes implement a concept where the user is looking through a
window at the current line. The window width is the value of COLUMNS if
it is defined, otherwise 80. If the line is longer than the window width
minus two, a mark is displayed at the end of the window to notify the
user. As the cursor moves and reaches the window boundaries the window
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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 the <Ctrl-F> sequence. This is entered by holding
down <Ctrl> (control) and pressing <F>. The <Shift> is not pressed. (The
notation ^? indicates <Delete>.)
The notation for escape sequences is M- followed by a character. For
example, M-f (Meta f) is entered by pressing <Esc> followed by <F>. (M-F
is the notation for pressing <Esc> followed by <Shift> <F>.)
All edit commands operate from any place on the line (not just at the
beginning). Neither <Return> nor <Line Feed> is pressed 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 backward to character char on current line.
^x^x Interchange the cursor and mark.
erase (User defined erase character as defined by the stty command,
usually ^h or #.) Delete previous character.
^d Delete current character.
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M-d Delete current word.
M-^h (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-delete) Delete previous word (if your interrupt
character is the default ^? or <Delete> 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 lowercase.
^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 the given position up to the
cursor. If preceded by a numerical parameter whose value is
greater than the current cursor position, then delete from the
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 linefeed (useful when using paper terminals).
^y Restore last item removed from line. (Yank item back to the
line.)
^l Linefeed and print current line.
^@ (Null character) Set mark.
M-space (Meta space) Set mark.
^j (Newline) 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.
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^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 0 is given, the search is forward.
The string is terminated by pressing <Return> or <Line Feed>.
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 0 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, ^n, ^], M-., M-
^], M-_, M-b, M-c, M-d, M-f, M-h, M-l and M-^h.
M-letter Soft-key - The 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 previous meta-functions (f, b, d, p, l, c, or h).
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 filename 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 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.
M-= List files matching current word pattern as if an asterisk
were appended.
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^u Multiply parameter of next command by 4.
\ Escape the 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 vi typing modes. Initially, when you enter a command you
are in the input mode. To edit, you enter control mode by pressing <Esc>,
moving the cursor to the point needing correction, then inserting or
deleting 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 if 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.
By default, the editor is in input mode. The following are input
commands:
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 the next character. Editing characters and 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.
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The following motion edit commands 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 nonblank character in line.
$ Cursor to end of line.
% Moves to balancing (, ), {, }, [, or ]. If the cursor is not
on one of the previously described characters, the remainder
of the line is searched first for the first occurrence of one
of these characters.
The following search edit commands access command history:
[count]k Fetch previous command. Each time k is entered the previous
command back in time is accessed.
[count]- Equivalent to k.
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[count]j Fetch next command. Each time j is entered the next command
forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The default is the least
recent history command.
/string Search backward through history for a previous command
containing string. String is terminated by pressing <Return>
or <Line Feed>. 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.
The following text change edit commands 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.
[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.
D Delete the current character through the end of line. Equivalent
to d$.
i Enter input mode and insert text before the current character.
I Insert text before the beginning of the line. Equivalent to 0i.
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[count]P
Place the previous text modification before the cursor.
[count]p
Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen with
characters you type overlay fashion.
[count]rc
Replace the count character(s) starting at the current cursor
position with c, and advance the cursor.
[count]x
Delete current character.
[count]X
Delete preceding character.
[count].
Repeat the previous text modification command.
[count]~
Invert the case of the count character(s) starting at the current
cursor position and advance the cursor.
[count]_
Causes the count word of the previous command to be appended and
input mode entered. The last word is used if count is omitted.
[count]
Delete count characters starting at the current cursor position,
and enter input mode.
* Causes an * to be appended to the current word and filename
generation attempted. If no match is found, it rings the bell.
Otherwise, the word is replaced by the matching pattern and input
mode is entered.
\ Filename completion. Replaces the current word with the longest
common prefix of all filenames matching the current word with an
asterisk appended. If the match is unique, a / is appended if the
file is a directory and a space is appended if the file is not a
directory.
The following miscellaneous commands may also be used:
[count]ymotion
y[count]motion
Yank current character through character that motion would move the
cursor to and puts them into the delete buffer. The text and
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cursor are unchanged.
Y Yanks from current position to end of line. Equivalent to y$.
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 Linefeed and print current line. Has effect only in control mode.
^J (Newline) 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.
= Lists the filenames that match the current word as if an asterisk
were appended to it.
@ 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 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 value, when there is
no syntax error, is 0. Commands that are preceded by one or two daggers
(†) are treated specially in the following ways:
⊕ Variable assignment lists preceding the command remain in effect when
the command completes.
⊕ I/O redirections are processed after variable assignments.
⊕ Errors cause the script to abort.
Additionally, in commands preceded by ††, words are expanded with the same
rules as a variable assignment. This means that tilde substitution is
performed after the = sign, and that word splitting and filename
generation are not performed.
† : [arg ... ]
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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] ... ]
The alias command with no arguments prints the list of aliases in
the form name=value on stdout. 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
value is 0 if name is not specified. If the name specified has no
value and no alias assigned to it, the exit value is nonzero.
bg [job ... ]
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 nth enclosing
loop.
cd [arg]
cd old new
This command can be in either of two forms. In the first form it
changes the current directory to arg. If arg is - the directory is
changed to the previous directory. The shell variable HOME is the
default arg. The variable PWD is set to the current directory.
The shell variable CDPATH defines the search path for the directory
containing arg. Alternative directory names are separated by a
colon (:). The default path is <null> (specifying the current
directory). Note that the current directory is specified by a null
pathname, which can appear immediately after the equal sign or
between the colon delimiters anywhere else in the path list. If
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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 krsh.
echo [arg ... ]
See the echo command for usage and description.
† eval [arg ... ]
The arguments are read as input to the shell and the resulting
commands 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 turned on (See
information in the following text on set).
†† 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] 1
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 -l flag is
selected, the commands are listed on stdout. Otherwise, the editor
program ename is invoked on a file containing these keyboard
commands. If ename is not supplied, then the value of the variable
FCEDIT (default /bin/ed) is used as the editor. When editing is
complete, the edited commands are executed. If last is not
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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 -r flag reverses the order of the commands and the -n
flag suppresses command numbers when listing. In the second form
the command is re-executed after the substitution old=new is
performed.
fg [job]
The 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. The optstring argument 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.
The getopts command 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 nonzero 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 (see 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), and the job or
process is stopped, the shell will send a CONT (continue) signal as
well as a terminate or hang up signal if it is stopped. The
argument job can be the process ID of a process that is not a
member of one of the active jobs. See "Jobs" for a description of
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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").
The exit status is 0 if the value of the last expression is
nonzero, 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 stdout 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 stdout. The -s
option causes the arguments to be written onto the history file
instead of stdout. The -u flag can be used to specify a one digit
file descriptor unit number n on which the output will be placed.
The default is 1. If the flag -n is used, no newline is added to
the output.
pwd Equivalent to print -r - $PWD.
read [-prsu[n]] [name?prompt] [name ...]
The shell input mechanism. One line is read and is broken up into
fields using the characters in IFS as separators. In raw mode, -r,
a \ at the end of a line does not signify line continuation. The
first field is assigned to the first name, the second field to the
second name, and so on, with leftover fields assigned to the last
name. The -p option causes the input line to be taken from the
input pipe of a process spawned by the shell using |&. If the -s
flag is present, the input will be saved as a command in the
history file. The flag -u can be used to specify a one digit file
descriptor unit n 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. 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 stderr when the shell
is interactive. The exit value is 0 unless an end-of-file is
encountered.
†† readonly [name[=value] ... ]
The given names are marked read-only and these names cannot be
changed by subsequent assignment.
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† return [n]
Causes a shell function to return to the invoking script with the
return status specified by n. If n is omitted then the return
status is that of the last command executed. If return is invoked
while not in a function or a . script, then it is the same as an
exit.
set [+aefhkmnopstuvx] [+o option ... ] [+A name] [arg ... ]
The flags for this command have meaning as follows:
-A Array assignment; unsets the variable name (if it has a value)
and assigns values sequentially from the list arg. If +A is
used, the variable name is not unset first.
-a Automatically exports all subsequent variables that are
defined.
-e If a command has a nonzero exit status, executes the ERR trap,
if set, and exits. This mode is disabled while reading
profiles.
-f Disables filename generation.
-h Makes each command a tracked alias when first encountered.
-k Places all variable assignment arguments in the environment
for a command, not just those that precede the command name.
-m Runs background jobs in a separate process group and prints a
line 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 Reads commands and checks them for syntax errors, but does not
execute them. Ignored for interactive shells.
-o Sets option name, using one of the following arguments:
allexport Same as -a flag
errexit Same as -e flag.
bgnice Runs all background jobs at a lower priority.
This is the default mode.
emacs Activates an emacs style inline editor for command
entry.
gmacs Activates a gmacs style inline editor for command
entry.
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ignoreeof Keeps the shell from exiting on end-of-file;
forces use of the exit command.
keyword Same as -k flag.
markdirs Appends a trailing / to all directory names
resulting from filename generation.
monitor Same as -m flag.
noclobber Prevents redirection > from truncating existing
files; requires >| to truncate a file when turned
on.
noexec Same as -n flag.
noglob Same as -f flag.
nolog Does not save function definitions in history
file.
nounset Same as -u flag.
privileged Same as -p flag.
verbose Same as -v flag.
trackall Same as -h flag.
vi Activates insert mode of a vi style inline editor
until you press <Esc>; this activates control
mode.
viraw Processes each character as it is typed in vi
mode.
xtrace Same as -x flag.
If no option name is supplied, then the current option
settings are printed.
-p Disables processing of the $HOME/.profile file and uses the
file /etc/suid_profile instead of the ENV file. This mode is
on whenever the effective UID/GID is not equal to the real
UID/GID. Turning this off causes the effective UID and GID to
be set to the real UID and GID.
-s Sorts the positional parameters lexicographically.
-t Exits after reading and executing one command.
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-u Treats unset parameters as an error when substituting.
-v Prints shell input lines as they are read.
-x Prints commands and their arguments as they are executed.
- Turns off -x and -v flags and stops examining arguments for
flags.
-- Does not change any of the flags; useful in setting $1 to a
value beginning with -. If no arguments follow this flag, the
positional parameters are unset.
Using + rather than - causes these flags to be turned off. These
flags can also be used upon invocation of the shell. The current
set of flags may be found in $-. Unless -A is specified, the
remaining arguments are positional parameters and are assigned, in
order, to $1, $2, ... . If no arguments are given then the names
and values of all variables are printed on stdout.
† 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 ... ]
The arg argument is a command to be read and executed when the
shell receives the signal 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 the traps for each
sig are reset to their original values. If arg is the null string
(""), 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 nonzero exit status. If sig is DEBUG then arg will
be executed after each command. If sig is 0 or EXIT and the trap
statement is executed inside the body of a function, then the
command arg is executed after the function completes. If sig is 0
or EXIT for a trap set outside any function then the command arg is
executed on exit from the shell. The trap command with no
arguments prints a list of commands associated with each signal
number.
†† typeset [+HLRZfilrtux[n]] [name[=value] ... ]
Sets attributes and values for shell variables and functions. When
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invoked inside a function, a new instance of the variables name is
created. The variables value and type are restored when the
function completes. The following list of attributes may be
specified:
-H Provides UNIX to hostname file mapping on non-UNIX machines.
-L Left-justifies and removes leading blanks from value. If n is
nonzero it defines the width of the field; otherwise, it is
determined by the width of the value of the first assignment.
When the variable is assigned, it is padded 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-justifies and fills with leading blanks. If n is
nonzero it defines the width of the field; otherwise, it is
determined by the width of the value of first assignment. The
field is padded from the left with blanks or truncated if the
variable is reassigned. The -L flag is turned off.
-Z Right-justifies and fills with leading zeros if the first
nonblank character is a digit and the -L flag has not been
set. If n is nonzero it defines the width of the field;
otherwise, it is determined by the width of the value of first
assignment.
-f Refer names to function names rather than to variable names.
No assignments can be made and the only other valid flags are
-t, -u, and -x. The -t flag turns on execution tracing for
this function. The -u flag causes this function to be marked
undefined. The FPATH variable will be searched to find the
function definition when the function is referenced. The -x
flag allows the function definition to remain in effect across
shell procedures invoked by name.
-i Defintes parameter as an integer; this makes arithmetic
faster. If n is nonzero, it defines the output arithmetic
base; otherwise, the first assignment determines the output
base.
-l Converts all uppercase characters to lowercase. The uppercase
flag, -u, is turned off.
-r Marks the given names read-only; these names cannot be changed
by subsequent assignment.
-t Tags the variables. Tags are user-definable and have no
special meaning to the shell.
-u Converts all lowercase characters to uppercase characters.
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The lowercase flag, -l, is turned off.
-x Marks the given names for automatic export to the environment
of subsequently-executed commands.
Using + rather than - causes these flags to be turned off. If name
arguments are not specified but flags are specified, a list of
names (and optionally the values) of the variables which have these
flags set is printed. (Using + rather than - keeps the values from
being printed.) If neither names nor flags are given, the names
and attributes of all variables are printed.
ulimit Sets or displays the number of 512-byte blocks of files written by
both parent and child processes. The default ulimit is printed
when no limit argument is given. The system default ulimit is set
at login time within /etc/profile, and may be changed by the system
administrator. Note: the ulimit command with no flag is the same
as the ulimit -f command.
umask [mask]
The user file-creation mask is set to mask (see the umask()
function). The mask paramter can either be an octal number or a
symbolic value as described in the chmod command. 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 aliases given by the list of names are removed from the alias
list.
unset [-f] name ...
The variables given by the list of names are unassigned; that is,
their values and attributes are erased. A variable must have a
value before it can be unset. Read-only variables cannot be unset.
If the -f flag is set, then the names refer to function names.
Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM,
SECONDS, TMOUT, and _ removes their special meaning even if they
are subsequently assigned to.
† wait [job]
Waits for the specified job to complete and reports its termination
status. If job is not given then all currently active child
processes are waited for. The exit value of 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.
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The -v flag produces a more verbose report.
The -p flag 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() and the first character of argument zero
($0) is -, then the shell is assumed to be a login shell and commands are
read from /etc/profile and then from either .profile in the current
directory or $HOME/.profile, if either file exists. Next, commands are
read from the file named by performing parameter substitution on the value
of the environment variable ENV if the file exists. If the -s flag is not
present and arg is, then a path search is performed on the first arg to
determine the name of the script to execute. The script arg must have
read permission and any setuid and getgid settings will be ignored.
Commands are then read as described in the following text; the following
flags are interpreted by the shell when it is invoked:
-c string Commands are read from string.
-s Commands are read from stdin. Commands are also read from
stdin if no arguments remain. Shell output, except for the
output of the special commands, is written to file descriptor
2 (see "Special Commands").
-i Starts an interactive shell. An interactive shell is also
sterted is the shell input and output are attached to a
terminal (as indicated by the ioctl() function). 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 Starts a restricted shell.
The remaining flags and arguments are described in the information on the
set commands (see "Special Commands").
Restricted Korn Shell
The Restricted Korn Shell (krsh) is used to set up login names and
execution environments that are more controlled than those of the standard
shell. The actions of krsh are almost identical to those of ksh; only the
following actions are not allowed:
⊕ Changing directories.
⊕ Setting the value of SHELL, ENV, or PATH.
⊕ Specifying path or command names containing /.
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⊕ Redirecting output (using >, >|, <>, and >>).
These restrictions are enforced after .profile and the ENV files are
interpreted.
When a restricted user issues a command that is found to be a shell
procedure, krsh invokes ksh to execute it. This makes it possible to
impose a limited set of commands on the restricted user, while providing
that user with shell procedures that have access to the full power of the
standard shell. This scheme assumes that the restricted user does not
have write and execute permissions in the same directory.
The writer of the restricted user's .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 can set up a directory of commands (for example,
/usr/rbin) that can be safely invoked by krsh.
FILES
/etc/passwd
User password file.
/etc/profile
System profile file.
$HOME/.profile
User profile file.
/tmp/sh*
Temporary files used by the shell.
/dev/null
Character special file generally used for unwanted output.
NOTES
If a command that 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
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executed. Therefore, alias and unalias commands in the file will not
apply to any functions defined in the file.
Traps are not processed while a job is waiting for a foreground process.
Thus, a trap on CHLD won't be executed until the foreground job
terminates.
EXIT VALUES
Errors detected by the shell, such as syntax errors, cause the shell to
return a nonzero exit value. Otherwise, the shell returns the exit value
of the last command executed (see previous information on the exit
command).
If the shell is being used non-interactively, execution of the shell 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 in which the error
occurred follows line 1, then the line number is also printed in square
brackets (for example, [25]) after the command or function name.
RELATED INFORMATION
Commands: cat(1), cd(1), chmod(1), cut(1), echo(1), emacs(1), env(1),
gmacs(1), newgrp(8), stty(1), test(1), umask(1), vi(1), paste(1), ls(1),
exec(1), cut(1), nice(1)
Functions: dup(2), exec(2), fork(2), ioctl(2), lseek(2), pipe(2),
signal(2), umask(2), ulimit(2), wait(2), rand(3)
Files: a.out(4), environ(4), profile(4)
Morris I. Bolsky and David G. Korn, The KornShell Command and Programming
Language, Prentice Hall, 1989
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