ksh(1) ksh(1)
NAME
ksh, rksh - KornShell, a standard/restricted command and
programming language
SYNOPSIS
ksh [ +aefhikmnprstuvx ] [ +o option ] ... [ -c string ] [
arg ... ]
rksh [ +aefhikmnprstuvx ] [ +o option ] ... [ -c string ] [
arg ... ]
DESCRIPTION
ksh is a command and programming language that executes com-
mands read from a terminal or a file. Rksh is a restricted
version of the command interpreter ksh; it is used to set up
login names and execution environments whose capabilities
are more controlled than those of the standard shell. See
Invocation below for the meaning of arguments to the shell.
Definitions.
A metacharacter is one of the following characters:
; & ( ) | < > new-line space tab
A blank is a tab or a space. An identifier is a sequence of
letters, digits, or underscores starting with a letter or
underscore. Identifiers are used as names for functions and
variables. A word is a sequence of characters separated by
one or more non-quoted metacharacters.
A command is a sequence of characters in the syntax of the
shell language. The shell reads each command and carries
out the desired action either directly or by invoking
separate utilities. A special command is a command that is
carried out by the shell without creating a separate pro-
cess. Except for documented side effects, most special com-
mands can be implemented as separate utilities.
Commands.
A simple-command is a sequence of blank separated words
which may be preceded by a variable assignment list (see
Environment below). The first word specifies the name of
the command to be executed. Except as specified below, the
remaining words are passed as arguments to the invoked com-
mand. 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 ter-
minates abnormally [see signal(2) for a list of status
values].
A pipeline is a sequence of one or more commands separated
by |. The standard output of each command but the last is
connected by a pipe(2) to the standard input of the next
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command. Each command is run as a separate process; the
shell waits for the last command to terminate. The exit
status of a pipeline is the exit status of the last command.
A list is a sequence of one or more pipelines separated by
;, &, &&, or ||, and optionally terminated by ;, &, or |&.
Of these five symbols, ;, &, and |& have equal precedence,
which is lower than that of && and ||. The symbols && and
|| also have equal precedence. A semicolon (;) causes
sequential execution of the preceding pipeline; an ampersand
(&) causes asynchronous execution of the preceding pipeline
(i.e., the shell does not wait for that pipeline to finish).
The symbol |& causes asynchronous execution of the preceding
command or pipeline with a two-way pipe established to the
parent shell. The standard input and output of the spawned
command can be written to and read from by the parent Shell
using the -p option of the special commands read and print
described later. The symbol && (||) causes the list follow-
ing it to be executed only if the preceding pipeline returns
a zero (non-zero) value. An arbitrary number of new-lines
may appear in a list, instead of a semicolon, to delimit a
command.
A command is either a simple-command or one of the follow-
ing. Unless otherwise stated, the value returned by a com-
mand is that of the last simple-command executed in the com-
mand.
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 posi-
tional parameters are used instead (see Parameter Sub-
stitution below). The PS3 prompt is printed and a line
is read from the standard input. If this line consists
of the number of one of the listed words, then the
value of the parameter identifier is set to the word
corresponding to this number. If this line is empty
the selection list is printed again. Otherwise the
value of the parameter identifier is set to null. The
contents of the line read from standard input is saved
in the variable REPLY. The list is executed for each
selection until a break or end-of-file is encountered.
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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 pat-
terns is the same as that used for file-name generation
(see File Name Generation below).
if list ;then list [ elif list ;then list ] ... [ ;else list ] ;fi
The list following if is executed and, if it returns a
zero exit status, the list following the first then is
executed. Otherwise, the list following elif is exe-
cuted 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 ter-
minates. If no commands in the do list are executed,
then the while command returns a zero exit status;
until may be used in place of while to negate the loop
termination test.
(list)
Execute list in a separate environment. Note, that if
two adjacent open parentheses are needed for nesting, a
space must be inserted to avoid arithmetic evaluation
as described below.
{ list;}
list is simply executed. The { must be followed by a
space. Note that unlike the metacharacters ( and ), {
and } are reserved words and must be typed at the
beginning of a line or after a ; in order to be recog-
nized.
[[expression]]
Evaluates expression and returns a zero exit status
when expression is true. See Conditional Expressions
below, for a description of expression.
function identifier { list ;}
identifier () { list ;}
Define a function which is referenced by identifier.
The body of the function is the list of commands
between { and }. (see Functions below). The { must be
followed by a space.
time pipeline
The pipeline is executed and the elapsed time as well
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as the user and system time are printed on standard
error.
The following reserved words are only recognized as the
first word of a command and when not quoted:
if then else elif fi case esac for while until do done { }
function select time [[ ]]
Comments.
A word beginning with # causes that word and all the follow-
ing characters up to a new-line to be ignored.
Aliasing.
The first word of each command is replaced by the text of an
alias if an alias for this word has been defined. An alias
name consists of any number of characters excluding meta-
characters, quoting characters, file expansion characters,
parameter and command substitution characters and =. The
replacement string can contain any valid Shell script
including the metacharacters listed above. The first word
of each command in the replaced text, other than any that
are in the process of being replaced, will be tested for
aliases. If the last character of the alias value is a
blank then the word following the alias will also be checked
for alias substitution. Aliases can be used to redefine
special builtin commands but cannot be used to redefine the
reserved words listed above. Aliases can be created,
listed, and exported with the alias command and can be
removed with the unalias command. Exported aliases remain
in effect for scripts invoked by name, but must be reini-
tialized for separate invocations of the Shell (see Invoca-
tion below).
Aliasing is performed when scripts are read, not while they
are executed. Therefore, for an alias to take effect the
alias definition command has to be executed before the com-
mand which references the alias is read.
Aliases are frequently used as a short hand for full path
names. An option to the aliasing facility allows the value
of the alias to be automatically set to the full pathname of
the corresponding command. These aliases are called tracked
aliases. The value of a tracked alias is defined the first
time the corresponding command is looked up and becomes
undefined each time the PATH variable is reset. These
aliases remain tracked so that the next subsequent reference
will redefine the value. Several tracked aliases are com-
piled into the shell. The -h option of the set command
makes each referenced command name into a tracked alias.
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The following exported aliases are compiled into the shell
but can be unset or redefined:
autoload='typeset -fu'
false='let 0'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
nohup='nohup '
r='fc -e -'
true=':'
type='whence -v'
Tilde Substitution.
After alias substitution is performed, each word is checked
to see if it begins with an unquoted ~. If it does, then
the word up to a / is checked to see if it matches a user
name in the /etc/passwd file. If a match is found, the ~
and the matched login name is replaced by the login direc-
tory of the matched user. This is called a tilde substitu-
tion. If no match is found, the original text is left
unchanged. A ~ by itself, or in front of a /, is replaced
by $HOME. A ~ followed by a + or - is replaced by $PWD and
$OLDPWD respectively.
In addition, tilde substitution is attempted when the value
of a variable assignment begins with a ~.
Command Substitution.
The standard output from a command enclosed in parentheses
preceded by a dollar sign ( $() ) or a pair of grave accents
(``) may be used as part or all of a word; trailing new-
lines are removed. In the second (archaic) form, the string
between the quotes is processed for special quoting charac-
ters before the command is executed (see Quoting below).
The command substitution $(cat file) can be replaced by the
equivalent but faster $(<file). Command substitution of
most special commands that do not perform input/output
redirection are carried out without creating a separate pro-
cess.
An arithmetic expression enclosed in double parentheses and
preceded by a dollar sign [$(())] is replaced by the value
of the arithmetic expression within the double parentheses.
Parameter Substitution.
A parameter is an identifier, one or more digits, or any of
the characters *, @, #, ?, -, $, and !. A variable (a
parameter denoted by an identifier) has a value and zero or
more attributes. Variables can be assigned values and
attributes by using the typeset special command. The attri-
butes supported by the Shell are described later with the
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typeset special command. Exported parameters pass values
and attributes to the environment.
The shell supports a one-dimensional array facility. An
element of an array variable is referenced by a subscript.
A subscript is denoted by a [, followed by an arithmetic
expression (see Arithmetic Evaluation below) followed by a
]. To assign values to an array, use set -A name value ...
. The value of all subscripts must be in the range of 0
through 1023. Arrays need not be declared. Any reference
to a variable with a valid subscript is legal and an array
will be created if necessary. Referencing an array without
a subscript is equivalent to referencing the element zero.
The value of a variable may also be assigned by writing:
name=value [ name=value ] ...
If the integer attribute, -i, is set for name the value is
subject to arithmetic evaluation as described below.
Positional parameters, parameters denoted by a number, may
be assigned values with the set special command. Parameter
$0 is set from argument zero when the shell is invoked.
The character $ is used to introduce substitutable parame-
ters.
${parameter}
The shell reads all the characters from ${ to the
matching } as part of the same word even if it contains
braces or metacharacters. The value, if any, of the
parameter is substituted. The braces are required when
parameter is followed by a letter, digit, or underscore
that is not to be interpreted as part of its name or
when a variable is subscripted. If parameter is one or
more digits then it is a positional parameter. A posi-
tional parameter of more than one digit must be
enclosed in braces. If parameter is * or @, then all
the positional parameters, starting with $1, are sub-
stituted (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 param-
eters is substituted. Otherwise, the length of the
value of the parameter is substituted.
${#identifier[*]}
The number of elements in the array identifier is sub-
stituted.
${parameter:-word}
If parameter is set and is non-null then substitute its
value; otherwise substitute word.
${parameter:=word}
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If parameter is not set or is null then set it to word;
the value of the parameter is then substituted. Posi-
tional 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 sub-
stituted. In the first form the smallest matching pat-
tern is deleted and in the second form the largest
matching pattern is deleted.
${parameter%pattern}
${parameter%%pattern}
If the Shell pattern matches the end of the value of
parameter, then the value of this substitution is the
value of the parameter with the matched part deleted;
otherwise substitute the value of parameter. In the
first form the smallest matching pattern is deleted and
in the second form the largest matching pattern is
deleted.
In the above, word is not evaluated unless it is to be used
as the substituted string, so that, in the following exam-
ple, pwd is executed only if d is not set or is null:
echo ${d:-$(pwd)}
If the colon ( : ) is omitted from the above expressions,
then the shell only checks whether parameter is set or not.
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
- Flags supplied to the shell on invocation or by
the set command.
? The decimal value returned by the last executed
command.
$ The process number of this shell.
Initially, the value is an absolute pathname of
the shell or script being executed as passed in
the environment. Subsequently it is assigned the
last argument of the previous command. This
parameter is not set for commands which are asyn-
chronous. This parameter is also used to hold the
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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 depen-
dent 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 com-
mand.
OPTARG
The value of the last option argument processed by
the getopts special command.
OPTIND
The index of the last option argument processed by
the getopts special command.
PPID The process number of the parent of the shell.
PWD The present working directory set by the cd com-
mand.
RANDOM
Each time this variable is referenced, a random
integer, uniformly distributed between 0 and
32767, is generated. The sequence of random
numbers can be initialized by assigning a numeric
value to RANDOM.
REPLY
This variable is set by the select statement and
by the read special command when no arguments are
supplied.
SECONDS
Each time this variable is referenced, the number
of seconds since shell invocation is returned. If
this variable is assigned a value, then the value
returned upon reference will be the value that was
assigned plus the number of seconds since the
assignment.
The following variables are used by the shell:
CDPATH
The search path for the cd command.
COLUMNS
If this variable is set, the value is used to
define the width of the edit window for the shell
edit modes and for printing select lists.
EDITOR
If the value of this variable ends in vi and the
VISUAL variable is not set, then the corresponding
option (see Special Command set below) will be
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turned on.
ENV If this variable is set, then parameter substitu-
tion is performed on the value to generate the
pathname of the script that will be executed when
the shell is invoked (see Invocation below). This
file is typically used for alias and function
definitions.
FCEDIT
The default editor name for the fc command.
FPATH
The search path for function definitions. This
path is searched when a function with the -u
attribute is referenced and when a command is not
found. If an executable file is found, then it is
read and executed in the current environment.
IFS Internal field separators, normally space, tab,
and new-line that is used to separate command
words which result from command or parameter sub-
stitution and for separating words with the spe-
cial command read. The first character of the IFS
variable is used to separate arguments for the
"$*" substitution (see Quoting below).
HISTFILE
If this variable is set when the shell is invoked,
then the value is the pathname of the file that
will be used to store the command history (see
Command re-entry below).
HISTSIZE
If this variable is set when the shell is invoked,
then the number of previously entered commands
that are accessible by this shell will be greater
than or equal to this number. The default is 128.
HOME The default argument (home directory) for the cd
command.
LINES
If this variable is set, the value is used to
determine the column length for printing select
lists. Select lists will print vertically until
about two-thirds of LINES lines are filled.
MAIL If this variable is set to the name of a mail file
and the MAILPATH variable is not set, then the
shell informs the user of arrival of mail in the
specified file.
MAILCHECK
This variable specifies how often (in seconds) the
shell will check for changes in the modification
time of any of the files specified by the MAILPATH
or MAIL variables. The default value is 600
seconds. When the time has elapsed the shell will
check before issuing the next prompt.
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MAILPATH
A colon ( : ) separated list of file names. If
this variable is set then the shell informs the
user of any modifications to the specified files
that have occurred within the last MAILCHECK
seconds. Each file name can be followed by a ?
and a message that will be printed. The message
will undergo parameter substitution with the vari-
able, $ defined as the name of the file that has
changed. The default message is you have mail in
$_.
PATH The search path for commands (see Execution
below). The user may not change PATH if executing
under rksh (except in .profile).
PS1 The value of this variable is expanded for parame-
ter substitution to define the primary prompt
string which by default is ``$ ''. The character
! in the primary prompt string is replaced by the
command number (see Command Re-entry below).
PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop,
by default ``#? ''.
PS4 The value of this variable is expanded for parame-
ter substitution and precedes each line of an exe-
cution trace. If omitted, the execution trace
prompt is ``+ ''.
SHELL
The pathname of the shell is kept in the environ-
ment. At invocation, if the basename of this
variable matches the pattern *r*sh, then the shell
becomes restricted.
TMOUT
If set to a value greater than zero, the shell
will terminate if a command is not entered within
the prescribed number of seconds after issuing the
PS1 prompt. (Note that the shell can be compiled
with a maximum bound for this value which cannot
be exceeded.)
VISUAL
If the value of this variable ends in vi then the
corresponding option (see Special Command set
below) will be turned on.
The shell gives default values to PATH, PS1, PS2, MAILCHECK,
TMOUT and IFS. HOME, MAIL and SHELL are set by login(1).
Blank Interpretation.
After parameter and command substitution, the results of
substitutions are scanned for the field separator characters
( those found in IFS ) and split into distinct arguments
where such characters are found. Explicit null arguments
("" or '') are retained. Implicit null arguments (those
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resulting from parameters that have no values) are removed.
File Name Generation.
Following substitution, each command word is scanned for the
characters *, ?, and [ unless the -f option has been set.
If one of these characters appears then the word is regarded
as a pattern. The word is replaced with lexicographically
sorted file names that match the pattern. If no file name
is found that matches the pattern, then the word is left
unchanged. When a pattern is used for file name generation,
the character . at the start of a file name or immediately
following a /, as well as the character / itself, must be
matched explicitly. In other instances of pattern matching
the / and . are not treated specially.
* Matches any string, including the null string.
? Matches any single character.
[...]
Matches any one of the enclosed characters. A
pair of characters separated by - matches any
character lexically between the pair, inclusive.
If the first character following the opening "[ "
is a "!" then any character not enclosed is
matched. A - can be included in the character set
by putting it as the first or last character.
A pattern-list is a list of one or more patterns separated
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 pat-
terns.
+(pattern-list)
Matches one or more occurrences of the given pat-
terns.
@(pattern-list)
Matches exactly one of the given patterns.
!(pattern-list)
Matches anything, except one of the given pat-
terns.
Quoting.
Each of the metacharacters listed above (see Definitions
above) has a special meaning to the shell and causes termi-
nation of a word unless quoted. A character may be quoted
(i.e., made to stand for itself) by preceding it with a \.
The pair \new-line is removed. All characters enclosed
between a pair of single quote marks (''), are quoted. A
single quote cannot appear within single quotes. Inside
double quote marks (""), parameter and command substitution
occurs and \ quotes the characters \, `, ", and $. The
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meaning of $* and $@ is identical when not quoted or when
used as a variable assignment value or as a file name. How-
ever, when used as a command argument, "$*" is equivalent to
"$1d$2d...", where d is the first character of the IFS vari-
able, whereas "$@" is equivalent to "$1"d"$2"d... Inside
grave quote marks (``) \ quotes the characters \, `, and $.
If the grave quotes occur within double quotes then \ also
quotes the character ".
The special meaning of reserved words or aliases can be
removed by quoting any character of the reserved word. The
recognition of function names or special command names
listed below cannot be altered by quoting them.
Arithmetic Evaluation.
An ability to perform integer arithmetic is provided with
the special command let. Evaluations are performed using
long arithmetic. Constants are of the form [base#]n where
base is a decimal number between two and thirty-six
representing the arithmetic base and n is a number in that
base. If base# is omitted then base 10 is used.
An arithmetic expression uses the same syntax, precedence,
and associativity of expression of the C language. All the
integral operators, other than ++, --, ?:, and , are sup-
ported. Variables can be referenced by name within an
arithmetic expression without using the parameter substitu-
tion 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 pre-
cisely, ((...)) is equivalent to let "...".
Prompting.
When used interactively, the shell prompts with the parame-
ter expanded value of PS1 before reading a command. If at
any time a new-line is typed and further input is needed to
complete a command, then the secondary prompt (i.e., the
value of PS2) is issued.
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Conditional Expressions.
A conditional expression is used with the [[ compound com-
mand to test attributes of files and to compare strings.
Word splitting and file name generation are not performed on
the words between [[ and ]]. Each expression can be con-
structed from one or more of the following unary or binary
expressions:
-a file True, if file exists.
-b file True, if file exists and is a block special file.
-c file True, if file exists and is a character special
file.
-d file True, if file exists and is a directory.
-f file True, if file exists and is an ordinary file.
-g file True, if file exists and has its setgid bit set.
-k file True, if file exists and has its sticky bit set.
-l file True, if file exists and is a symbolic link.
-n string True, if length of string is non-zero.
-o option True, if option named option is on.
-p file True, if file exists and is a fifo special file or
a pipe.
-r file True, if file exists and is readable by current
process.
-s file True, if file exists and has size greater than
zero.
-t fildes True, if file descriptor number fildes is open and
associated with a terminal device.
-u file True, if file exists and is has its setuid bit
set.
-w file True, if file exists and is writable by current
process.
-x file True, if file exists and is executable by current
process. If file exists and is a directory, then
the current process has permission to search in
the directory.
-z string True, if length of string is zero.
-L file True, if file exists and is a symbolic link.
-O file True, if file exists and is owned by the effective
user id of this process.
-G file True, if file exists and its group matches the
effective group id of this process.
-S file True, if file exists and is a socket.
file1 -nt file2
True, if file1 exists and is newer than file2.
file1 -ot file2
True, if file1 exists and is older than file2.
file1 -ef file2
True, if file1 and file2 exist and refer to the
same file.
string = pattern
True, if string matches pattern.
string != pattern
True, if string does not match pattern.
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string1 < string2
True, if string1 comes before string2 based on
ASCII value of their characters.
string1 > string2
True, if string1 comes after string2 based on
ASCII value of their characters.
exp1 -eq exp2
True, if exp1 is equal to exp2.
exp1 -ne exp2
True, if exp1 is not equal to exp2.
exp1 -lt exp2
True, if exp1 is less than exp2.
exp1 -gt exp2
True, if exp1 is greater than exp2.
exp1 -le exp2
True, if exp1 is less than or equal to exp2.
exp1 -ge exp2
True, if exp1 is greater than or equal to exp2.
In each of the above expressions, if file is of the form
/dev/fd/n, where n is an integer, then the test applied to
the open file whose descriptor number is n.
A compound expression can be constructed from these primi-
tives by using any of the following, listed in decreasing
order of precedence.
(expression)
True, if expression is true. Used to group expres-
sions.
! expression
True if expression is false.
expression1 && expression2
True, if expression1 and expression2 are both true.
expression1 || expression2
True, if either expression1 or expression2 is true.
Input/Output.
Before a command is executed, its input and output may be
redirected using a special notation interpreted by the
shell. The following may appear anywhere in a simple-
command or may precede or follow a command and are not
passed on to the invoked command. Command and parameter
substitution occurs before word or digit is used except as
noted below. File name generation occurs only if the pat-
tern matches a single file and blank interpretation is not
performed.
<word Use file word as standard input (file descrip-
tor 0).
>word Use file word as standard output (file
descriptor 1). If the file does not exist
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then it is created. If the file exists, is a
regular file, and the noclobber option is on,
this causes an error; otherwise, it is trun-
cated to zero length.
>|word Sames as >, except that it overrides the
noclobber option.
>>word Use file word as standard output. If the file
exists then output is appended to it (by first
seeking to the end-of-file); otherwise, the
file is created.
<>word Open file word for reading and writing as
standard input.
<<[-]word The shell input is read up to a line that is
the same as word, or to an end-of-file. No
parameter substitution, command substitution
or file name generation is performed on word.
The resulting document, called a here-
document, becomes the standard input. If any
character of word is quoted, then no interpre-
tation is placed upon the characters of the
document; otherwise, parameter and command
substitution occurs, \new-line is ignored, and
\ must be used to quote the characters \, $,
`, and the first character of word. If - is
appended to <<, then all leading tabs are
stripped from word and from the document.
<&digit The standard input is duplicated from file
descriptor digit [see dup(2)]. Similarly for
the standard output using >& digit.
<&- The standard input is closed. Similarly for
the standard output using >&-.
<&p The input from the co-process is moved to
standard input.
>&p The output to the co-process is moved to stan-
dard output.
If one of the above is preceded by a digit, then the file
descriptor number referred to is that specified by the digit
(instead of the default 0 or 1). For example:
... 2>&1
means file descriptor 2 is to be opened for writing as a
duplicate of file descriptor 1.
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The order in which redirections are specified is signifi-
cant. The shell evaluates each redirection in terms of the
(file descriptor, file) association at the time of evalua-
tion. 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 redirec-
tions 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 execu-
tion of a command contains the file descriptors of the
invoking shell as modified by input/output specifications.
Environment.
The environment [see environ(5)] is a list of name-value
pairs that is passed to an executed program in the same way
as a normal argument list. The names must be identifiers
and the values are character strings. The shell interacts
with the environment in several ways. On invocation, the
shell scans the environment and creates a variable for each
name found, giving it the corresponding value and marking it
export . Executed commands inherit the environment. If the
user modifies the values of these variables or creates new
ones, using the export or typeset -x commands they become
part of the environment. The environment seen by any exe-
cuted command is thus composed of any name-value pairs ori-
ginally inherited by the shell, whose values may be modified
by the current shell, plus any additions which must be noted
in export or typeset -x commands.
The environment for any simple-command or function may be
augmented by prefixing it with one or more variable assign-
ments. A variable assignment argument is a word of the form
identifier=value. Thus:
TERM=450 cmd args and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is con-
cerned except for commands listed with one or two daggers,
†, in the Special Commands section).
If the -k flag is set, all variable assignment arguments are
placed in the environment, even if they occur after the com-
mand name. The following first prints a=b c and then c:
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echo a=b c
set -k
echo a=b c
This feature is intended for use with scripts written for
early versions of the shell and its use in new scripts is
strongly discouraged. It is likely to disappear someday.
Functions.
The function reserved word, described in the Commands sec-
tion above, is used to define shell functions. Shell func-
tions 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 param-
eters (see Execution below).
Functions execute in the same process as the caller and
share all files and present working directory with the
caller. Traps caught by the caller are reset to their
default action inside the function. A trap condition that
is not caught or ignored by the function causes the function
to terminate and the condition to be passed on to the
caller. A trap on EXIT set inside a function is executed
after the function completes in the environment of the
caller. Ordinarily, variables are shared between the cal-
ling program and the function. However, the typeset special
command used within a function defines local variables whose
scope includes the current function and all functions it
calls.
The special command return is used to return from function
calls. Errors within functions return control to the
caller.
Function identifiers can be listed with the -f or +f option
of the typeset special command. The text of functions may
also be listed with -f. Function can be undefined with the
-f option of the unset special command.
Ordinarily, functions are unset when the shell executes a
shell script. The -xf option of the typeset command allows
a function to be exported to scripts that are executed
without a separate invocation of the shell. Functions that
need to be defined across separate invocations of the shell
should be specified in the ENV file with the -xf option of
typeset.
Jobs.
If the monitor option of the set command is turned on, an
interactive shell associates a job with each pipeline. It
keeps a table of current jobs, printed by the jobs command,
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and assigns them small integer numbers. When a job is
started asynchronously with &, the shell prints a line which
looks like:
[1] 1234
indicating that the job which was started asynchronously was
job number 1 and had one (top-level) process, whose process
id was 1234.
If you are running a job and wish to do something else you
may hit the key ^Z (ctrl-z) which sends a STOP signal to the
current job. The shell will then normally indicate that the
job has been `Stopped', and print another prompt. You can
then manipulate the state of this job, putting it in the
background with the bg command, or run some other commands
and then eventually bring the job back into the foreground
with the foreground command fg. A ^Z takes effect immedi-
ately 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 giv-
ing the command ``stty tostop''. If you set this tty
option, then background jobs will stop when they try to pro-
duce output like they do when they try to read input.
There are several ways to refer to jobs in the shell. A job
can be referred to by the process id of any process of the
job or by one of the following:
%number
The job with the given number.
%string
Any job whose command line begins with string.
%?string
Any job whose command line contains string.
%% Current job.
%+ Equivalent to %%.
%- Previous job.
This shell learns immediately whenever a process changes
state. It normally informs you whenever a job becomes
blocked so that no further progress is possible, but only
just before it prints a prompt. This is done so that it
does not otherwise disturb your work.
When the monitor mode is on, each background job that com-
pletes triggers any trap set for CHLD.
When you try to leave the shell while jobs are running or
stopped, you will be warned that `You have stopped(running)
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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 variable PATH defines the search path for the
directory containing the command. Alternative directory
names are separated by a colon (:). The default path is
/usr/bin: (specifying /usr/bin and the current directory in
that order). The current directory can be specified by two
or more adjacent colons, or by a colon at the beginning or
end of the path list. If the command name contains a / then
the search path is not used. Otherwise, each directory in
the path is searched for an executable file. If the file
has execute permission but is not a directory or an a.out
file, it is assumed to be a file containing shell commands.
A sub-shell is spawned to read it. All non-exported
aliases, functions, and variables, are removed in this case.
A parenthesized command is executed in a sub-shell without
removing non-exported quantities.
Command Re-entry.
The text of the last HISTSIZE (default 128) commands entered
from a terminal device is saved in a history file. The file
$HOME/.shhistory is used if the file denoted by the HIST-
FILE 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
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be edited or listed can be selected by number or by giving
the first character or characters of the command. A single
command or range of commands can be specified. If you do
not specify an editor program as an argument to fc then the
value of the variable FCEDIT is used. If FCEDIT is not
defined then /usr/bin/ed is used. The edited command(s) is
printed and re-executed upon leaving the editor. The editor
name - is used to skip the editing phase and to re-execute
the command. In this case a substitution variable of the
form old=new can be used to modify the command before execu-
tion. For example, if r is aliased to 'fc -e -' then typing
`r bad=good c' will re-execute the most recent command which
starts with the letter c, replacing the first occurrence of
the string bad with the string good.
In-line Editing Options
Normally, each command line entered from a terminal device
is simply typed followed by a new-line (`RETURN' or
`LINE FEED'). If the vi option is active, the user can edit
the command line. To be in this edit mode set the vi
option. An editing option is automatically selected each
time the VISUAL or EDITOR variable is assigned a value end-
ing in either of these option names.
The editing features require that the user's terminal accept
`RETURN' as carriage return without line feed and that a
space (` ') must overwrite the current character on the
screen. ADM terminal users should set the "space - advance"
switch to `space'. Hewlett-Packard series 2621 terminal
users should set the straps to `bcGHxZ etX'.
The editing mode implements a concept where the user is
looking through a window at the current line. The window
width is the value of COLUMNS if it is defined, otherwise
80. If the line is longer than the window width minus two,
a mark is displayed at the end of the window to notify the
user. As the cursor moves and reaches the window boundaries
the window will be centered about the cursor. The mark is a
> (<, *) if the line extends on the right (left, both)
side(s) of the window.
The search commands in each edit mode provide access to the
history file. Only strings are matched, not patterns,
although a leading ^ in the string restricts the match to
begin at the first character in the line.
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
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control characters or escape sequences. The notation for
control characters is caret ( ^ ) followed by the character.
For example, ^F is the notation for CTRL-f. This is entered
by depressing `f' while holding down the `CTRL' (control)
key. (The notation ^? indicates the DEL (delete) key.)
The notation for escape sequences is M- followed by a char-
acter. For example, M-f (pronounced Meta f) is entered by
depressing ESC (ascii \033) followed by `f'. (M-F would be
the notation for ESC followed by `SHIFT' (capital) `F'.)
All edit commands operate from any place on the line (not
just at the beginning). Neither the "RETURN" nor the "LINE
FEED" key is entered after edit commands except when noted.
^F Move cursor forward (right) one character.
M-f Move cursor forward one word. (The emacs editor's
idea of a word is a string of characters consist-
ing of only letters, digits and underscores.)
^B Move cursor backward (left) one character.
M-b Move cursor backward one word.
^A Move cursor to start of line.
^E Move cursor to end of line.
^]char Move cursor forward to character char on current
line.
M-^]char Move cursor back to character char on current
line.
^X^X Interchange the cursor and mark.
erase (User defined erase character as defined by the
stty(1) command, usually ^H or #.) Delete previ-
ous character.
^D Delete current character.
M-d Delete current word.
M-^H (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-DEL) Delete previous word (if your interrupt
character is ^? (DEL, the default) then this com-
mand will not work).
^T Transpose current character with next character in
emacs mode. Transpose two previous characters in
gmacs mode.
^C Capitalize current character.
M-c Capitalize current word.
M-l Change the current word to lower case.
^K Delete from the cursor to the end of the line. If
preceded by a numerical parameter whose value is
less than the current cursor position, then delete
from given position up to the cursor. If preceded
by a numerical parameter whose value is greater
than the current cursor position, then delete from
cursor up to given cursor position.
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^W Kill from the cursor to the mark.
M-p Push the region from the cursor to the mark on the
stack.
kill (User defined kill character as defined by the
stty command, usually ^G or @.) Kill the entire
current line. If two kill characters are entered
in succession, all kill characters from then on
cause a line feed (useful when using paper termi-
nals).
^Y Restore last item removed from line. (Yank item
back to the line.)
^L Line feed and print current line.
^@ (Null character) Set mark.
M-space (Meta space) Set mark.
^J (New line) Execute the current line.
^M (Return) Execute the current line.
eof End-of-file character, normally ^D, is processed
as an End-of-file only if the current line is
null.
^P Fetch previous command. Each time ^P is entered
the previous command back in time is accessed.
Moves back one line when not on the first line of
a multi-line command.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command line. Each time ^N is entered
the next command line forward in time is accessed.
^Rstring Reverse search history for a previous command line
containing string. If a parameter of zero is
given, the search is forward. String is ter-
minated by a "RETURN" or "NEW LINE". If string is
preceded by a ^, the matched line must begin with
string. If string is omitted, then the next com-
mand line containing the most recent string is
accessed. In this case a parameter of zero rev-
erses the direction of the search.
^O Operate - Execute the current line and fetch the
next line relative to current line from the his-
tory file.
M-digits (Escape) Define numeric parameter, the digits are
taken as a parameter to the next command. The
commands that accept a parameter are ^F, ^B,
erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-,
M-b, M-c, M-d, M-f, M-h M-l and M-^H.
M-letter Soft-key - Your alias list is searched for an
alias by the name letter and if an alias of this
name is defined, its value will be inserted on the
input queue. The letter must not be one of the
above meta-functions. M-]letter Soft-key - Your
alias list is searched for an alias by the name
letter and if an alias of this name is defined,
its value will be inserted on the input queue.
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The can be used to program functions keys on many
terminals.
M-. The last word of the previous command is inserted
on the line. If preceded by a numeric parameter,
the value of this parameter determines which word
to insert rather than the last word.
M- Same as M-..
M-* Attempt file name generation on the current word.
An asterisk is appended if the word doesn't match
any file or contain any special pattern charac-
ters.
M-ESC File name completion. Replaces the current word
with the longest common prefix of all filenames
matching the current word with an asterisk
appended. If the match is unique, a / is appended
if the file is a directory and a space is appended
if the file is not a directory.
M-= List files matching current word pattern if an
asterisk were appended.
^U Multiply parameter of next command by 4.
\ Escape next character. Editing characters, the
user's erase, kill and interrupt (normally ^?)
characters may be entered in a command line or in
a search string if preceded by a \. The \ removes
the next character's editing features (if any).
^V Display version of the shell.
M-# Insert a # at the beginning of the line and exe-
cute it. This causes a comment to be inserted in
the history file.
Vi Editing Mode
There are two typing modes. Initially, when you enter a
command you are in the input mode. To edit, the user enters
control mode by typing ESC (\033) and moves the cursor to
the point needing correction and then inserts or deletes
characters or words as needed. Most control commands accept
an optional repeat count prior to the command.
When in vi mode on most systems, canonical processing is
initially enabled and the command will be echoed again if
the speed is 1200 baud or greater and it contains any con-
trol characters or less than one second has elapsed since
the prompt was printed. The ESC character terminates canon-
ical 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 echo-
ing of raw mode.
If the option viraw is also set, the terminal will always
have canonical processing disabled.
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Input Edit Commands
By default the editor is in input mode.
erase (User defined erase character as defined by
the stty command, usually ^H or #.) Delete
previous character.
^W Delete the previous blank separated word.
^D Terminate the shell.
^V Escape next character. Editing characters,
the user's erase or kill characters may be
entered in a command line or in a search
string if preceded by a ^V. The ^V removes
the next character's editing features (if
any).
\ Escape the next erase or kill character.
Motion Edit Commands
These commands will move the cursor.
[count]l Cursor forward (right) one character.
[count]w Cursor forward one alpha-numeric word.
[count]W Cursor to the beginning of the next word that
follows a blank.
[count]e Cursor to end of word.
[count]E Cursor to end of the current blank delimited
word.
[count]h Cursor backward (left) one character.
[count]b Cursor backward one word.
[count]B Cursor to preceding blank separated word.
[count]| Cursor to column count.
[count]fc Find the next character c in the current
line.
[count]Fc Find the previous character c in the current
line.
[count]tc Equivalent to f followed by h.
[count]Tc Equivalent to F followed by l.
[count]; Repeats count times, the last single charac-
ter find command, f, F, t, or T.
[count], Reverses the last single character find com-
mand count times.
0 Cursor to start of line.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is
entered the previous command back in time is
accessed.
[count]- Equivalent to k.
[count]j Fetch next command. Each time j is entered
the next command forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The
default is the least recent history command.
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/string Search backward through history for a previ-
ous command containing string. String is
terminated by a "RETURN" or "NEW LINE". If
string is preceded by a ^, the matched line
must begin with string. If string is null
the previous string will be used.
?string Same as / except that search will be in the
forward direction.
n Search for next match of the last pattern to
/ or ? commands.
N Search for next match of the last pattern to
/ or ?, but in reverse direction. Search
history for the string entered by the previ-
ous / 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 $a.
[count]cmotion
c[count]motion
Delete current character through the charac-
ter that motion would move the cursor to and
enter input mode. If motion is c, the entire
line will be deleted and input mode entered.
C Delete the current character through the end
of line and enter input mode. Equivalent to
c$.
S Equivalent to cc.
D Delete the current character through the end
of line. Equivalent to d$.
[count]dmotion
d[count]motion
Delete current character through the charac-
ter that motion would move to. If motion is
d, the entire line will be deleted.
i Enter input mode and insert text before the
current character.
I Insert text before the beginning of the line.
Equivalent to 0i.
[count]P Place the previous text modification before
the cursor.
[count]p Place the previous text modification after
the cursor.
R Enter input mode and replace characters on
the screen with characters you type overlay
fashion.
[count]rc Replace the count character(s) starting at
the current cursor position with c, and
advance the cursor.
[count]x Delete current character.
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[count]X Delete preceding character.
[count]. Repeat the previous text modification com-
mand.
[count]~ Invert the case of the count character(s)
starting at the current cursor position and
advance the cursor.
[count] Causes the count word of the previous command
to be appended and input mode entered. The
last word is used if count is omitted.
* Causes an * to be appended to the current
word and file name generation attempted. If
no match is found, it rings the bell. Other-
wise, the word is replaced by the matching
pattern and input mode is entered.
\ Filename completion. Replaces the current
word with the longest common prefix of all
filenames matching the current word with an
asterisk appended. If the match is unique, a
/ is appended if the file is a directory and
a space is appended if the file is not a
directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion
Yank current character through character that
motion would move the cursor to and puts them
into the delete buffer. The text and cursor
are unchanged.
Y Yanks from current position to end of line.
Equivalent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands per-
formed 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, regard-
less of mode.
^M (Return) Execute the current line, regardless
of mode.
# Sends the line after inserting a # in front
of the line. Useful for causing the current
line to be inserted in the history without
being executed.
= List the file names that match the current
word if an asterisk were appended it.
@letter Your alias list is searched for an alias by
the name letter and if an alias of this name
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is defined, its value will be inserted on the
input queue for processing.
Special Commands.
The following simple-commands are executed in the shell pro-
cess. Input/Output redirection is permitted. Unless other-
wise indicated, the output is written on file descriptor 1
and the exit status, when there is no syntax error, is zero.
Commands that are preceded by one or two † are treated spe-
cially in the following ways:
1. Variable assignment lists preceding the command remain
in effect when the command completes.
2. I/O redirections are processed after variable assign-
ments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by †† that are in
the format of a variable assignment, are expanded with
the same rules as a variable assignment. This means
that tilde substitution is performed after the = sign
and word splitting and file name generation are not
performed.
† : [ arg ... ]
The command only expands parameters.
† . file [ arg ... ]
Read the complete file then execute the commands. The
commands are executed in the current Shell environment.
The search path specified by PATH is used to find the
directory containing file. If any arguments arg are
given, they become the positional parameters. Other-
wise the positional parameters are unchanged. The exit
status is the exit status of the last command executed.
†† alias [ -tx ] [ name[ =value ] ] ...
Alias with no arguments prints the list of aliases in
the form name=value on standard output. An alias is
defined for each name whose value is given. A trailing
space in value causes the next word to be checked for
alias substitution. The -t flag is used to set and
list tracked aliases. The value of a tracked alias is
the full pathname corresponding to the given name. The
value becomes undefined when the value of PATH is reset
but the aliases remain tracked. Without the -t flag,
for each name in the argument list for which no value
is given, the name and value of the alias is printed.
The -x flag is used to set or print exported aliases.
An exported alias is defined for scripts invoked by
name. The exit status is non-zero if a name is given,
but no value, for which no alias has been defined.
bg [ job... ]
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This command is only on systems that support job con-
trol. Puts each specified job into the background.
The current job is put in the background if job is not
specified. See Jobs for a description of the format of
job.
† break [ n ]
Exit from the enclosing for, while, until or select
loop, if any. If n is specified then break n levels.
† continue [ n ]
Resume the next iteration of the enclosing for, while,
until or select loop. If n is specified then resume at
the n-th enclosing loop.
cd [ arg ]
cd old new
This command can be in either of two forms. In the
first form it changes the current directory to arg. If
arg is - the directory is changed to the previous
directory. The shell variable HOME is the default arg.
The variable PWD is set to the current directory. The
shell variable CDPATH defines the search path for the
directory containing arg. Alternative directory names
are separated by a colon (:). The default path is
<null> (specifying the current directory). Note that
the current directory is specified by a null path name,
which can appear immediately after the equal sign or
between the colon delimiters anywhere else in the path
list. If arg begins with a / then the search path is
not used. Otherwise, each directory in the path is
searched for arg.
The second form of cd substitutes the string new for the
string old in the current directory name, PWD and tries to
change to this new directory.
The cd command may not be executed by rksh.
echo [ arg ... ]
See echo(1) for usage and description.
† eval [ arg ... ]
The arguments are read as input to the shell and the
resulting command(s) executed.
† exec [ arg ... ]
If arg is given, the command specified by the arguments
is executed in place of this shell without creating a
new process. Input/output arguments may appear and
affect the current process. If no arguments are given
the effect of this command is to modify file
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descriptors as prescribed by the input/output redirec-
tion list. In this case, any file descriptor numbers
greater than 2 that are opened with this mechanism are
closed when invoking another program.
† exit [ n ]
Causes the shell to exit with the exit status specified
by n. If n is omitted then the exit status is that of
the last command executed. An end-of-file will also
cause the shell to exit except for a shell which has
the ignoreeof option (see set below) turned on.
†† export [ name[=value] ] ...
The given names are marked for automatic export to the
environment of subsequently-executed commands.
fc [ -e ename ] [ -nlr ] [ first [ last ] ]
fc -e - [ old=new ] [ command ]
In the first form, a range of commands from first to
last is selected from the last HISTSIZE commands that
were typed at the terminal. The arguments first and
last may be specified as a number or as a string. A
string is used to locate the most recent command start-
ing 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 stan-
dard 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 vari-
able FCEDIT (default /usr/bin/ed) is used as the edi-
tor. When editing is complete, the edited command(s)
is executed. If last is not specified then it will be
set to first. If first is not specified the default is
the previous command for editing and -16 for listing.
The flag -r reverses the order of the commands and the
flag -n suppresses command numbers when listing. In
the second form the command is re-executed after the
substitution old=new is performed.
fg [ job... ]
This command is only on systems that support job con-
trol. Each job specified is brought to the foreground.
Otherwise, the current job is brought into the fore-
ground. See Jobs for a description of the format of
job.
getopts optstring name [ arg ... ]
Checks arg for legal options. If arg is omitted, the
positional parameters are used. An option argument
begins with a + or a -. An option not beginning with +
or - or the argument -- ends the options. optstring
contains the letters that getopts recognizes. If a
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letter is followed by a :, that option is expected to
have an argument. The options can be separated from
the argument by blanks.
getopts places the next option letter it finds inside
variable name each time it is invoked with a +
prepended when arg begins with a +. The index of the
next arg is stored in OPTIND. The option argument, if
any, gets stored in OPTARG.
A leading : in optstring causes getopts to store the
letter of an invalid option in OPTARG, and to set name
to ? for an unknown option and to : when a required
option is missing. Otherwise, getopts prints an error
message. The exit status is non-zero when there are no
more options.
jobs [ -lnp ] [ job ... ]
Lists information about each given job; or all active
jobs if job is omitted. The -l flag lists process ids
in addition to the normal information. The -n flag
only displays jobs that have stopped or exited since
last notified. The -p flag causes only the process
group to be listed. See Jobs for a description of the
format of job.
kill [ -sig ] job ...
kill -l
Sends either the TERM (terminate) signal or the speci-
fied signal to the specified jobs or processes. Sig-
nals are either given by number or by names (as given
in /usr/include/signal.h, stripped of the prefix
``SIG''). If the signal being sent is TERM (terminate)
or HUP (hangup), then the job or process will be sent a
CONT (continue) signal if it is stopped. The argument
job can be the process id of a process that is not a
member of one of the active jobs. See Jobs for a
description of the format of job. In the second form,
kill -l, the signal numbers and names are listed.
let arg ...
Each arg is a separate arithmetic expression to be
evaluated. See Arithmetic Evaluation above, for a
description of arithmetic expression evaluation.
The exit status is 0 if the value of the last expres-
sion is non-zero, and 1 otherwise.
† newgrp [ arg ... ]
Equivalent to exec /usr/bin/newgrp arg ....
print [ -Rnprsu[n ] ] [ arg ... ]
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The shell output mechanism. With no flags or with flag
- or -- the arguments are printed on standard output as
described by echo(1). In raw mode, -R or -r, the
escape conventions of echo are ignored. The -R option
will print all subsequent arguments and options other
than -n. The -p option causes the arguments to be
written onto the pipe of the process spawned with |&
instead of standard output. The -s option causes the
arguments to be written onto the history file instead
of standard output. The -u flag can be used to specify
a one digit file descriptor unit number n on which the
output will be placed. The default is 1. If the flag
-n is used, no new-line is added to the output.
pwd Equivalent to print -r - $PWD
read [ -prsu[ n ] ] [ name?prompt ] [ name ... ]
The shell input mechanism. One line is read and is
broken up into fields using the characters in IFS as
separators. In raw mode, -r, a \ at the end of a line
does not signify line continuation. The first field is
assigned to the first name, the second field to the
second name, etc., with leftover fields assigned to the
last name. The -p option causes the input line to be
taken from the input pipe of a process spawned by the
shell using |&. If the -s flag is present, the input
will be saved as a command in the history file. The
flag -u can be used to specify a one digit file
descriptor unit to read from. The file descriptor can
be opened with the exec special command. The default
value of n is 0. If name is omitted then REPLY is used
as the default name. The exit status is 0 unless an
end-of-file is encountered. An end-of-file with the -p
option causes cleanup for this process so that another
can be spawned. If the first argument contains a ?,
the remainder of this word is used as a prompt on stan-
dard error when the shell is interactive. The exit
status is 0 unless an end-of-file is encountered.
†† readonly [ name[=value] ] ...
The given names are marked readonly and these names
cannot be changed by subsequent assignment.
† return [ n ]
Causes a shell function to return to the invoking
script with the return status specified by n. If n is
omitted then the return status is that of the last com-
mand executed. If return is invoked while not in a
function or a script, then it is the same as an exit.
set [ +aefhkmnpstuvx ] [ +o option ]... [ +A name ] [ arg ... ]
The flags for this command have meaning as follows:
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-A Array assignment. Unset the variable name and
assign values sequentially from the list arg. If
+A is used, the variable name is not unset first.
-a All subsequent variables that are defined are
automatically exported.
-e If a command has a non-zero exit status, execute
the ERR trap, if set, and exit. This mode is dis-
abled while reading profiles.
-f Disables file name generation.
-h Each command becomes a tracked alias when first
encountered.
-k All variable assignment arguments are placed in
the environment for a command, not just those that
precede the command name.
-m Background jobs will run in a separate process
group and a line will print upon completion. The
exit status of background jobs is reported in a
completion message. On systems with job control,
this flag is turned on automatically for interac-
tive shells.
-n Read commands and check them for syntax errors,
but do not execute them. Ignored for interactive
shells.
-o The following argument can be one of the following
option names:
allexport Same as -a.
errexit Same as -e.
bgnice All background jobs are run at a
lower priority. This is the default
mode.
emacs Puts you in an emacs style in-line
editor for command entry.
gmacs Puts you in a gmacs style in-line
editor for command entry.
ignoreeof The shell will not exit on end-of-
file. The command exit must be used.
keyword Same as -k.
markdirs All directory names resulting from
file name generation have a trailing
/ appended.
monitor Same as -m.
noclobber Prevents redirection > from truncat-
ing existing files. Require >| to
truncate a file when turned on.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in
history file.
nounset Same as -u.
privileged Same as -p.
verbose Same as -v.
trackall Same as -h.
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vi Puts you in insert mode of a vi style
in-line editor until you hit escape
character 033. This puts you in move
mode. A return sends the line.
viraw Each character is processed as it is
typed in vi mode.
xtrace Same as -x.
If no option name is supplied then the current
option settings are printed.
-p Disables processing of the $HOME/.profile file and
uses the file /etc/suidprofile instead of the ENV
file. This mode is on whenever the effective uid
(gid) is not equal to the real uid (gid). Turning
this off causes the effective uid and gid to be
set to the real uid and gid.
-s Sort the positional parameters lexicographically.
-t Exit after reading and executing one command.
-u Treat unset parameters as an error when substitut-
ing.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are
executed.
- Turns off -x and -v flags and stops examining
arguments for flags.
-- Do not change any of the flags; useful in setting
$1 to a value beginning with -. If no arguments
follow this flag then the positional parameters
are unset.
Using + rather than - causes these flags to be turned
off. These flags can also be used upon invocation of
the shell. The current set of flags may be found in
$-. Unless -A is specified, the remaining arguments
are positional parameters and are assigned, in order,
to $1 $2 .... If no arguments are given then the names
and values of all variables are printed on the standard
output.
† shift [ n ]
The positional parameters from $n+1 ... are renamed $1
... , default n is 1. The parameter n can be any
arithmetic expression that evaluates to a non-negative
number less than or equal to $#.
† times
Print the accumulated user and system times for the
shell and for processes run from the shell.
† trap [ arg ] [ sig ] ...
arg is a command to be read and executed when the shell
receives signal(s) sig. (Note that arg is scanned once
when the trap is set and once when the trap is taken.)
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Each sig can be given as a number or as the name of the
signal. Trap commands are executed in order of signal
number. Any attempt to set a trap on a signal that was
ignored on entry to the current shell is ineffective.
If arg is omitted or is -, then all trap(s) sig are
reset to their original values. If arg is the null
string then this signal is ignored by the shell and by
the commands it invokes. If sig is ERR then arg will
be executed whenever a command has a non-zero exit
status. sig is DEBUG then arg will be executed after
each command. If sig is 0 or EXIT and the trap state-
ment is executed inside the body of a function, then
the command arg is executed after the function com-
pletes. If sig is 0 or EXIT for a trap set outside any
function then the command arg is executed on exit from
the shell. The trap command with no arguments prints a
list of commands associated with each signal number.
†† typeset [ +HLRZfilrtux[n] ] [ name[ =value ] ] ...
Sets attributes and values for shell variables. When
invoked inside a function, a new instance of the vari-
able name is created. The parameter value and type are
restored when the function completes. The following
list of attributes may be specified:
-H This flag provides UNIX to host-name file mapping
on non-UNIX machines.
-L Left justify and remove leading blanks from value.
If n is non-zero it defines the width of the
field, otherwise it is determined by the width of
the value of first assignment. When the variable
is assigned to, it is filled on the right with
blanks or truncated, if necessary, to fit into the
field. Leading zeros are removed if the -Z flag
is also set. The -R flag is turned off.
-R Right justify and fill with leading blanks. If n
is non-zero it defines the width of the field,
otherwise it is determined by the width of the
value of first assignment. The field is left
filled with blanks or truncated from the end if
the variable is reassigned. The L flag is turned
off.
-Z Right justify and fill with leading zeros if the
first non-blank character is a digit and the -L
flag has not been set. If n is non-zero it
defines the width of the field, otherwise it is
determined by the width of the value of first
assignment.
-f The names refer to function names rather than
variable names. No assignments can be made and
the only other valid flags are -t, -u and -x. The
flag -t turns on execution tracing for this func-
tion. The flag -u causes this function to be
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marked undefined. The FPATH variable will be
searched to find the function definition when the
function is referenced. The flag -x allows the
function definition to remain in effect across
shell procedures invoked by name.
-i Variable is an integer. This makes arithmetic
faster. If n is non-zero it defines the output
arithmetic base, otherwise the first assignment
determines the output base.
-l All upper-case characters converted to lower-case.
The upper-case flag, -u is turned off.
-r The given names are marked readonly and these
names cannot be changed by subsequent assignment.
-t Tags the variables. Tags are user definable and
have no special meaning to the shell.
-u All lower-case characters are converted to upper-
case characters. The lower-case flag, -l is
turned off.
-x The given names are marked for automatic export to
the environment of subsequently-executed commands.
Using + rather than - causes these flags to be turned
off. If no name arguments are given but flags are
specified, a list of names (and optionally the values)
of the variables which have these flags set is printed.
(Using + rather than - keeps the values from being
printed.) If no names and flags are given, the names
and attributes of all variables are printed.
ulimit [ -[HS][a | cdfnpst] ]
ulimit prints or sets hard or soft resource limits.
These limits are described in getrlimit(2).
If limit is not present, ulimit prints the specified
limits. Any number of limits may be printed at one
time. The -a option prints all limits.
If limit is present, ulimit sets the specified limit to
limit. The string unlimited requests the largest valid
limit. Limits may be set for only one resource at a
time. Any user may set a soft limit to any value below
the hard limit. Any user may lower a hard limit. Only
the super-user may raise a hard limit; see su(1).
The -H option specifies a hard limit. The -S option
specifies a soft limit. If neither option is speci-
fied, ulimit will set both limits and print the soft
limit.
The following options specify the resource whose limits
are to be printed or set. If no option is specified,
the file size limit is printed or set.
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-c maximum core file size (in 512-byte blocks)
-d maximum size of data segment or heap (in kbytes)
-f maximum file size (in 512-byte blocks)
-n maximum file descriptor plus 1
-s maximum size of stack segment (in kbytes)
-t maximum CPU time (in seconds)
If no option is given, -f is assumed.
umask [ mask ]
The user file-creation mask is set to mask [see
umask(2)]. mask can either be an octal number or a
symbolic value as described in chmod(1). If a symbolic
value is given, the new umask value is the complement
of the result of applying mask to the complement of the
previous umask value. If mask is omitted, the current
value of the mask is printed.
unalias name ...
The variables given by the list of names are removed
from the alias list.
unset [ -f ] name ...
The variables given by the list of names are unas-
signed, i. e., their values and attributes are erased.
Read-only variables cannot be unset. If the flag, -f,
is set, then the names refer to function names. Unset-
ting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM,
SECONDS, TMOUT, and causes removes their special
meaning even if they are subsequently assigned to.
† wait [ job ]
Wait for the specified job and report its termination
status. If job is not given then all currently active
child processes are waited for. The exit status from
this command is that of the process waited for. See
Jobs for a description of the format of job.
whence [ -pv ] name ...
For each name, indicate how it would be interpreted if
used as a command name.
-v produces a more verbose report.
-p does a path search for name even if name is an
alias, a function, or a reserved word.
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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 substitu-
tion on the value of the environment variable ENV if the
file exists. If the -s flag is not present and arg is, then
a path search is performed on the first arg to determine the
name of the script to execute. The script arg must have
read permission and any setuid and setgid settings will be
ignored. Commands are then read as described below; the
following flags are interpreted by the shell when it is
invoked:
-c string If the -c flag is present then commands are read
from string.
-s If the -s flag is present or if no arguments
remain then commands are read from the standard
input. Shell output, except for the output of the
Special commands listed above, is written to file
descriptor 2.
-i If the -i flag is present or if the shell input
and output are attached to a terminal (as told by
ioctl(2)) then this shell is interactive. In this
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 res-
tricted shell.
The remaining flags and arguments are described under the
set command above.
Rksh Only.
Rksh is used to set up login names and execution environ-
ments whose capabilities are more controlled than those of
the standard shell. The actions of rksh are identical to
those of sh, except that the following are disallowed:
changing directory [see cd(1)],
setting the value of SHELL, ENV, or PATH,
specifying path or command names containing /,
redirecting output (>, >| , <> , and >>).
The restrictions above are enforced after .profile and the
ENV files are interpreted.
When a command to be executed is found to be a shell pro-
cedure, rksh invokes ksh to execute it. Thus, it is possi-
ble to provide to the end-user shell procedures that have
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access to the full power of the standard shell, while impos-
ing 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 perform-
ing 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 com-
mands (i.e., /usr/rbin) that can be safely invoked by rksh.
EXIT STATUS
Errors detected by the shell, such as syntax errors, cause
the shell to return a non-zero exit status. Otherwise, the
shell returns the exit status of the last command executed
(see also the exit command above). If the shell is being
used non-interactively then execution of the shell file is
abandoned. Run time errors detected by the shell are
reported by printing the command or function name and the
error condition. If the line number that the error occurred
on is greater than one, then the line number is also printed
in square brackets ([]) after the command or function name.
FILES
/etc/passwd
/etc/profile
/etc/suidprofile
$HOME/.profile
/tmp/sh*
/dev/null
SEE ALSO
cat(1), cd(1), chmod(1), cut(1), echo(1), env(1), paste(1),
stty(1), test(1), umask(1), and vi(1).
dup(2), exec(2), fork(2), ioctl(2), lseek(2), pipe(2), sig-
nal(2), umask(2), ulimit(2), wait(2), and rand(3C) in the
CX/UX Programmer's Reference Manual.
newgrp(1M), a.out(4), profile(4), and environ(4) in the
CX/UX Administrator's Reference Manual.
Morris I. Bolsky and David G. Korn, The KornShell Command
and Programming Language, Prentice Hall, 1989.
NOTES
If a command which is a tracked alias is executed, and then
a command with the same name is installed in a directory in
the search path before the directory where the original com-
mand was found, the shell will continue to exec the original
command. Use the -t option of the alias command to correct
this situation.
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Some very old shell scripts contain a ^ as a synonym for the
pipe character |.
Using the fc built-in command within a compound command will
cause the whole command to disappear from the history file.
The built-in command . file reads the whole file before any
commands are executed. Therefore, alias and unalias com-
mands in the file will not apply to any functions defined in
the file.
Traps are not processed while a job is waiting for a fore-
ground process. Thus, a trap on CHLD won't be executed
until the foreground job terminates.
Page 39 CX/UX User's Reference Manual