sh(1)sh(1)NAME
sh, rsh, ksh, rksh - a standard/restricted command and programming
language
SYNOPSISsh [ -abCefhikmnprstuvx ] [ -o option ] ... [ -c string ] [ arg ... ]
/usr/lib/rsh [ -abCefhikmnprstuvx ] [ -o option ] ... [ -c string ]
[ arg ... ]
DESCRIPTION
Note: As of IRIX 6.4, sh is the Korn shell rather than the Bourne shell.
See bsh(1) for the Bourne Shell description. See the COMPATIBILITY
ISSUES section below for more detail.
This is the internationalized sh. See the INTERNATIONALIZATION section
below for more detail.
sh is a command and programming language that executes commands read from
a terminal or a file. /usr/lib/rsh (also invoked as rksh) is a
restricted version of the standard command interpreter sh; 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:
; & ( ) | < > newline space tab
A blank is a tab or a space. An identifier is a sequence of letters,
digits, or underscores starting with a letter or underscore. Identifiers
are used as names for functions and variables. A word is a sequence of
characters separated by one or more non-quoted metacharacters.
A command is a sequence of characters in the syntax of the shell
language. The shell reads each command and carries out the desired
action either directly or by invoking separate utilities. A special
command is a command that is carried out by the shell without creating a
separate process. Except for documented side effects, most special
commands can be implemented as separate utilities.
Commands
A simple-command is a sequence of blank separated words which may be
preceded by a variable assignment list (see Environment below). The
first word specifies the name of the command to be executed. Except as
specified below, the remaining words are passed as arguments to the
invoked command. The command name is passed as argument 0 [see exec(2)].
The value of a simple-command is its exit status if it terminates
normally, or (octal) 200+status if it terminates abnormally [see
signal(2) for a list of status values].
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A pipeline is a sequence of one or more commands separated by |. The
standard output of each command but the last is connected by a pipe(2) to
the standard input of the next command. Each command is run as a
separate process; the shell waits for the last command to terminate. The
exit status of a pipeline is the exit status of the last command.
A list is a sequence of one or more pipelines separated by ;, &, &&, or
||, and optionally terminated by ;, &, or |&. Of these five symbols, ;,
&, and |& have equal precedence, which is lower than that of && and ||.
The symbols && and || also have equal precedence. A semicolon (;) causes
sequential execution of the preceding pipeline; an ampersand (&) causes
asynchronous execution of the preceding pipeline (that is, the shell does
not wait for that pipeline to finish). The symbol |& causes asynchronous
execution of the preceding command or pipeline with a two-way pipe
established to the parent shell. The standard input and output of the
spawned command can be written to and read from by the parent shell using
the -p option of the special commands read and print described later.
The symbol && (||) causes the list following it to be executed only if
the preceding pipeline returns a zero (nonzero) value. An arbitrary
number of newlines may appear in a list, instead of a semicolon, to
delimit a command.
A command is either a simple-command or one of the following. Unless
otherwise stated, the value returned by a command is that of the last
simple-command executed in the command.
for identifier [ in word ... ] ; do list ; done
Each time a for command is executed, identifier is set to the next
word taken from the in word list. If in word ... is omitted, 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, the positional parameters are used instead (see Parameter
Substitution below). The PS3 prompt is printed and a line is read
from the standard input. If this line consists of the number of one
of the listed words, the value of the parameter identifier is set to
the word corresponding to this number. If this line is empty the
selection list is printed again. Otherwise the value of the
parameter identifier is set to null. The contents of the line read
from standard input is saved in the variable REPLY. The list is
executed for each selection until a break or end-of-file is
encountered.
case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
A case command executes the list associated with the first pattern
that matches word. The form of the patterns is the same as that
used for file-name generation (see Filename Generation below).
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if list ; then list [ elif list ; then list ] ... [ ; else list ] ; fi
The list following if is executed and, if it returns a zero exit
status, the list following the first then is executed. Otherwise,
the list following elif is executed and, if its value is zero, the
list following the next then is executed. Failing that, the else
list is executed. If no else list or then list is executed, the if
command returns a zero exit status.
while list ; do list ; done
until list ; do list ; done
A while command repeatedly executes the while list and, if the exit
status of the last command in the list is zero, executes the do
list; otherwise the loop terminates. If no commands in the do list
are executed, the while command returns a zero exit status; until
may be used in place of while to negate the loop termination test.
(list)
Execute list in a separate environment. Note, that if two adjacent
open parentheses are needed for nesting, a space must be inserted to
avoid arithmetic evaluation as described below.
{ list;}
list is simply executed. The { must be followed by a space. Note
that unlike the metacharacters ( and ), { and } are reserved words
and must be typed at the beginning of a line or after a ; in order
to be recognized.
[[expression]]
Evaluates expression and returns a zero exit status when expression
is true. See Conditional Expressions below, for a description of
expression.
function identifier { list;}
identifier () { list;}
Define a function which is referenced by identifier. The body of
the function is the list of commands between { and } (see Functions
below). The { must be followed by a space.
time pipeline
The pipeline is executed and the elapsed time as well as the user
and system time are printed on standard error. Note that the
reported times reflect the elapsed time for both the parent and the
child processes in order to give a more accurate view of the total
time the pipeline took to execute.
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 [[ ]]
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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 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,
is tested for aliases. If the last character of the alias value is a
blank the word following the alias is also checked for alias
substitution. Aliases can be used to redefine special builtin commands
but cannot be used to redefine the reserved words listed above. Aliases
can be created, listed, and exported with the alias command and can be
removed with the unalias command. Exported aliases remain in effect for
scripts invoked by name, but must be reinitialized for separate
invocations of the shell (see Invocation below).
Aliasing is performed when scripts are read, not while they are executed.
Therefore, for an alias to take effect the alias definition command has
to be executed before the command which references the alias is read.
Aliases are frequently used as a short hand for full pathnames. 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 redefines 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'
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Tilde Substitution
After alias substitution is performed, each word is checked to see if it
begins with an unquoted ~. If it does, the word up to a / is checked to
see if it matches a user name in the /etc/passwd file. If a match is
found, the ~ and the matched login name is replaced by the login
directory of the matched user. This is called a tilde substitution. If
no match is found, the original text is left unchanged. A ~ by itself,
or in front of a /, is replaced by $HOME. A ~ followed by a + or - is
replaced by $PWD and $OLDPWD respectively.
In addition, tilde substitution is attempted when the value of a variable
assignment begins with a ~.
Tilde substitution is not supported in all shell invocations. (See the
COMPATIBILITY ISSUES section at the end of this document.)
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 newlines are removed. In the second (archaic)
form, the string between the quotes is processed for special quoting
characters before the command is executed (see Quoting below). Not all
forms of command substitution are supported in all shell invocations.
(See the COMPATIBILITY ISSUES section at the end of this document.) The
command substitution $(cat file) can be replaced by the equivalent but
faster $(<file). Command substitution of most special commands that do
not perform input/output redirection are carried out without creating a
separate process.
In some shell invocations, an arithmetic expression enclosed in double
parentheses and preceded by a dollar sign [$(())] is replaced by the
value of the arithmetic expression within the double parentheses. (See
the COMPATIBILITY ISSUES section at the end of this document for more
detail.)
Parameter Substitution
A parameter is an identifier, one or more digits, or any of the
characters *, @, #, ?, -, $, and !. A variable (a parameter denoted by
an identifier) has a value and zero or more attributes. Variables can be
assigned values and attributes by using the typeset special command. The
attributes supported by the shell are described later with the typeset
special command. Exported parameters pass values and attributes to the
environment.
The shell supports a one-dimensional array facility. An element of an
array variable is referenced by a subscript. A subscript is denoted by a
[, followed by an arithmetic expression (see Arithmetic Evaluation below)
followed by a ]. To assign values to an array, use
set -A name value ...
The value of all subscripts must be in the range of 0 through 1023.
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Arrays need not be declared. Any reference to a variable with a valid
subscript is legal and an array is created if necessary. Referencing an
array without a subscript is equivalent to referencing the element zero.
The value of a variable may also be assigned by writing:
name=value [ name=value ] ...
If the integer attribute, -i, is set for name the value is subject to
arithmetic evaluation as described below.
Positional parameters, parameters denoted by a number, may be assigned
values with the set special command. Parameter $0 is set from argument
zero when the shell is invoked.
The character $ is used to introduce substitutable parameters.
${parameter}
The shell reads all the characters from ${ to the matching } as part
of the same word even if it contains braces or metacharacters. The
value, if any, of the parameter is substituted. The braces are
required when parameter is followed by a letter, digit, or
underscore that is not to be interpreted as part of its name or when
a variable is subscripted. If parameter is one or more digits it is
a positional parameter. A positional parameter of more than one
digit must be enclosed in braces. If parameter is * or @, all the
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, substitute its value; otherwise
substitute word.
${parameter:=word}
If parameter is not set or is null, set it to word; the value of the
parameter is substituted. Positional parameters may not be assigned
to in this way.
${parameter:?word}
If parameter is set and is non-null, substitute its value;
otherwise, print word and exit from the shell. If word is omitted,
a standard message is printed.
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${parameter:+word}
If parameter is set and is non-null, substitute word; otherwise
substitute nothing.
${parameter#pattern}
${parameter##pattern}
If the shell pattern matches the beginning of the value of
parameter, the value of this substitution is the value of the
parameter with the matched portion deleted; otherwise the value of
this parameter is substituted. In the first form the smallest
matching pattern is deleted and in the second form the largest
matching pattern is deleted.
${parameter%pattern}
${parameter%%pattern}
If the shell pattern matches the end of the value of parameter, the
value of this substitution is the value of the parameter with the
matched part deleted; otherwise substitute the value of parameter.
In the first form the smallest matching pattern is deleted and in
the second form the largest matching pattern is deleted.
In the above, word is not evaluated unless it is to be used as the
substituted string, so that, in the following example, pwd is executed
only if d is not set or is null:
echo ${d:-$(pwd)}
If the colon (:) is omitted from the above expressions, the shell only
checks whether parameter is set or not.
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
- Flags supplied to the shell on invocation or by the set command.
? The decimal value returned by the last executed command.
$ The process number of this shell.
_ Initially, the value _ is an absolute pathname of the shell or
script being executed as passed in the environment.
Subsequently it is assigned the last argument of the previous
command. This parameter is not set for commands which are
asynchronous. This parameter is also used to hold the name of
the matching MAIL file when checking for mail.
! The process number of the last background command invoked.
ERRNO The value of errno as set by the most recently failed system
call. This value is system dependent and is intended for
debugging purposes.
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LINENO The line number of the current line within the script or
function being executed.
OLDPWD The previous working directory set by the cd command.
OPTARG The value of the last option argument processed by the getopts
special command.
OPTIND The index of the last option argument processed by the getopts
special command.
PPID The process number of the parent of the shell.
PWD The present working directory set by the cd command.
RANDOM Each time this variable is referenced, a random integer,
uniformly distributed between 0 and 32767, is generated. The
sequence of random numbers can be initialized by assigning a
numeric value to RANDOM.
REPLY This variable is set by the select statement and by the read
special command when no arguments are supplied.
SECONDS Each time this variable is referenced, the number of seconds
since shell invocation is returned. If this variable is
assigned a value, the value returned upon reference is 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, or vi and the
VISUAL variable is not set, the corresponding option (see
special command set below) is turned on.
ENV If this variable is set, parameter substitution is performed
on the value to generate the pathname of the script that will
be executed when the shell is invoked (see Invocation below).
This file is typically used for alias and function
definitions.
FCEDIT The default editor name for the fc command.
FPATH The search path for function definitions. This path is
searched when a function with the -u attribute is referenced
and when a command is not found. If an executable file is
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found, it is read and executed in the current environment.
IFS Internal field separators (normally space, tab, and newline)
used to separate command words that result from command or
parameter substitution and for separating words with the
special command read. The first character of the IFS
variable is used to separate arguments for the "$*"
substitution (see Quoting below).
HISTFILE If this variable is set when the shell is invoked, the value
is the pathname of the file that is used to store the command
history (see Command re-entry below).
HISTSIZE If this variable is set when the shell is invoked, the number
of previously entered commands that are accessible by this
shell is 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 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, the shell informs the user of
arrival of mail in the specified file.
MAILCHECK This variable specifies how often (in seconds) the shell
checks 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 checks before issuing the next prompt.
MAILPATH A colon ( : ) separated list of filenames. If this variable
is set 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 is printed. The message undergoes parameter
substitution with the variable, $_ defined as the name of the
file that has changed. The default message is you have mail
in $_.
PATH The search path for commands (see Execution below). The user
may not change PATH if executing under rsh (except in
.profile).
PS1 The value of this variable is expanded for parameter
substitution to define the primary prompt string which by
default is ``$ ''. The character ! in the primary prompt
string is replaced by the command number (see Command Re-
entry below).
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PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop, by default
``#? ''.
PS4 The value of this variable is expanded for parameter
substitution and precedes each line of an execution trace.
If omitted, the execution trace prompt is ``+ ''.
SHELL The pathname of the shell is kept in the environment. At
invocation, if the basename of this variable matches the
pattern *r*sh, the shell becomes restricted.
TMOUT If set to a value greater than zero, the shell terminates 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, or vi the
corresponding option (see special command set below) is
turned on.
_XPG The value of this variable controls certain features of the
shell. The default value is 0 (zero). (See the COMPATIBILITY
ISSUES section at the end of this document.)
The shell gives default values to PATH, PS1, PS2, MAILCHECK, _XPG, TMOUT
and IFS. HOME, MAIL and SHELL are set by login(1).
Blank Interpretation
After parameter and command substitution, the results of substitutions
are scanned for the field separator characters ( those found in IFS ) and
split into distinct arguments where such characters are found. Explicit
null arguments ("" or '') are retained. Implicit null arguments (those
resulting from parameters that have no values) are removed.
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, the 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, 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.
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? 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 "!" any character not enclosed is matched. A - can be included
in the character set by putting it as the first or last
character.
A pattern-list is a list of one or more patterns separated from each
other with a |. Composite patterns can be formed with one or more of the
following:
?(pattern-list) Optionally matches any one of the given patterns.
*(pattern-list) Matches zero or more occurrences of the given patterns.
+(pattern-list) Matches one or more occurrences of the given patterns.
@(pattern-list) Matches exactly one of the given patterns.
!(pattern-list) Matches anything, except one of the given patterns.
Quoting
Each of the metacharacters listed above (see Definitions above) has a
special meaning to the shell and causes termination of a word unless
quoted. A character may be quoted (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 quote marks (''), are quoted. A single
quote cannot appear within single quotes. Inside double quote marks
(""), parameter and command substitution occurs and \ quotes the
characters \, `, ", and $. The meaning of $* and $@ is identical when
not quoted or when used as a variable assignment value or as a filename.
However, when used as a command argument, "$*" is equivalent to
"$1d$2d...", where d is the first character of the IFS variable, whereas
"$@" is equivalent to "$1"d"$2"d... . Inside grave quote marks (``) \
quotes the characters \, `, and $. If the grave quotes occur within
double quotes, \ 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 base 10 is used.
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An arithmetic expression uses the same syntax, precedence, and
associativity of expression of the C language. All the integral
operators, other than ++, --, ?:, and , are supported. Variables can be
referenced by name within an arithmetic expression without using the
parameter substitution syntax. When a variable is referenced, its value
is evaluated as an arithmetic expression.
An internal integer representation of a variable can be specified with
the -i option of the typeset special command. Arithmetic evaluation is
performed on the value of each assignment to a variable with the -i
attribute. If you do not specify an arithmetic base, the first
assignment to the variable determines the arithmetic base. This base is
used when parameter substitution occurs.
Since many of the arithmetic operators require quoting, an alternative
form of the let command is provided. For any command which begins with a
((, all the characters until a matching )) are treated as a quoted
expression. More precisely, ((...)) is equivalent to let "...".
Prompting
When used interactively, the shell prompts with the parameter expanded
value of PS1 before reading a command. If at any time a newline is typed
and further input is needed to complete a command, the secondary prompt
(that is, 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.
-e file Same as -a file.
-f file True, if file exists and is an ordinary file.
-g file True, if file exists and is has its setgid bit set.
-k file True, if file exists and is has its sticky bit set.
-n string True, if length of string is 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 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.
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sh(1)sh(1)-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, 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.
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, the test is applied to the open file whose descriptor
number is n.
A compound expression can be constructed from these primitives by using
any of the following, listed in decreasing order of precedence.
(expression) True, if expression is true. Used to group
expressions.
! expression True if expression is false.
expression1 && expression2 True, if expression1 and expression2 are
both true.
expression1 || expression2 True, if either expression1 or expression2
is true.
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
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and are not passed on to the invoked command. Command and parameter
substitution occurs before word or digit is used except as noted below.
Filename generation occurs only if the pattern matches a single file and
blank interpretation is not performed.
<word Use file word as standard input (file descriptor 0).
>word Use file word as standard output (file descriptor 1). If the
file does not exist it is created. If the file exists, is a
regular file, and the noclobber option is on, this causes an
error; otherwise, it is truncated to zero length.
>|word Sames as >, except that it overrides the noclobber option.
>>word Use file word as standard output. If the file exists 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 filename generation is performed on
word. The resulting document, called a here-document,
becomes the standard input. If any character of word is
quoted, no interpretation is placed upon the characters of
the document; otherwise, parameter and command substitution
occurs, \newline is ignored, and \ must be used to quote the
characters \, $, `, and the first character of word. If - is
appended to <<, all leading tabs are stripped from word and
from the document.
<&digit The standard input is duplicated from file descriptor digit
[see dup(2)]. Similarly for the standard output using >&
digit.
<&- The standard input is closed. Similarly for the standard
output using >&-.
<&p The input from the co-process is moved to standard input.
>&p The output to the co-process is moved to standard output.
If one of the above is preceded by a digit, 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 significant. The shell
evaluates each redirection in terms of the (file descriptor, file)
association at the time of evaluation. For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then associates
file descriptor 2 with the file associated with file descriptor 1 (that
is, fname). If the order of redirections were reversed, file descriptor
2 is associated with the terminal (assuming file descriptor 1 had been)
and then file descriptor 1 is associated with file fname.
If a command is followed by & and job control is not active, the default
standard input for the command is the empty file /dev/null. Otherwise,
the environment for the execution of a command contains the file
descriptors of the invoking shell as modified by input/output
specifications.
Environment
The environment [see environ(5)] is a list of name-value pairs that is
passed to an executed program in the same way as a normal argument list.
The names must be identifiers and the values are character strings. The
shell interacts with the environment in several ways. On invocation, the
shell scans the environment and creates a variable for each name found,
giving it the corresponding value and marking it export . Executed
commands inherit the environment. If the user modifies the values of
these variables or creates new ones, using the export or typeset -x
commands they become part of the environment. The environment seen by
any executed command is thus composed of any name-value pairs originally
inherited by the shell, whose values may be modified by the current
shell, plus any additions which must be noted in export or typeset -x
commands.
The environment for any simple-command or function may be augmented by
prefixing it with one or more variable assignments. A variable
assignment argument is a word of the form identifier=value. Thus, the
commands:
TERM=450 cmd args
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is concerned except
for commands listed with one or two asterisks, * or **, in the Special
Commands section).
If the -k flag is set, all variable assignment arguments are placed in
the environment, even if they occur after the command name. The
following first prints a=b c and then c:
echo a=b c
set -k
echo a=b c
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This feature is intended for use with scripts written for early versions
of the shell and its use in new scripts is strongly discouraged. It is
likely to disappear someday.
Functions
The function reserved word, described in the Commands section above, is
used to define shell functions. Shell functions are read in and stored
internally. Alias names are resolved when the function is read.
Functions are executed like commands with the arguments passed as
positional parameters (see Execution below). Within a function, the
special positional parameter $0 may be the name of the invoking program
or the name of the function, depending on how the shell is invoked. (See
the COMPATIBILITY ISSUES section at the end of this document)
Functions execute in the same process as the caller and share all files
and present working directory with the caller. Traps caught by the
caller are reset to their default action inside the function. A trap
condition that is not caught or ignored by the function causes the
function to terminate and the condition to be passed on to the caller. A
trap on EXIT set inside a function is executed after the function
completes in the environment of the caller. Ordinarily, variables are
shared between the calling program and the function. However, the
typeset special command used within a function defines local variables
whose scope includes the current function and all functions it calls.
The special command return is used to return from function calls. Errors
within functions return control to the caller.
Function identifiers can be listed with the -f or +f option of the
typeset special command. The text of functions may also be listed with
-f. Function can be undefined with the -f option of the unset special
command.
Ordinarily, functions are unset when the shell executes a shell script.
The -xf option of the typeset command allows a function to be exported to
scripts that are executed without a separate invocation of the shell.
Functions that need to be defined across separate invocations of the
shell should be specified in the ENV file with the -xf option of typeset.
Jobs
If the monitor option of the set command is turned on, an interactive
shell associates a job with each pipeline. It keeps a table of current
jobs, printed by the jobs command, and assigns them small integer
numbers. The max number of jobs is defined by the systune value 'maxup'.
This is determined at shell invocation. When a job is started
asynchronously with &, the shell prints a line which looks like:
[1] 1234
indicating that the job which was started asynchronously was job number 1
and had one (top-level) process, whose process id was 1234.
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If you are running a job and wish to do something else you may hit the
key ^Z (CTRL-z) which sends a STOP signal to the current job. The shell
normally indicates that the job has been `Stopped', and prints another
prompt. You can manipulate the state of this job, putting it in the
background with the bg command or run some other commands and 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 stops 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, background jobs stop when they try to produce output
like they do when they try to read input.
There are several ways to refer to jobs in the shell. A job can be
referred to by the process id of any process of the job or by one of the
following:
%number The job with the given number.
%string Any job whose command line begins with string.
%?string Any job whose command line contains string.
%% Current job.
%+ Equivalent to %%.
%- Previous job.
This shell learns immediately whenever a process changes state. It
normally informs you whenever a job becomes blocked so that no further
progress is possible, but only just before it prints a prompt. This is
done so that it does not otherwise disturb your work.
When the monitor mode is on, each background job that completes triggers
any trap set for CHLD.
When you try to leave the shell while jobs are running or stopped, you
are be warned that `You have stopped(running) jobs.' You may use the
jobs command to see what they are. If you do this or immediately try to
exit again, the shell does not warn you a second time, and the stopped
jobs are terminated.
Signals
When a command is run in the background (that it, when it is followed by
&) and the job monitor option is active, the command does not receive
INTERRUPT or QUIT signals. When a command is run in the background (that
it, when it is followed by &) and the job monitor option is not active,
the command receives INTERRUPT or QUIT signals but ignores them.
Otherwise, signals have the values inherited by the shell from its parent
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(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 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 / 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/.sh_history
is used if the file denoted by the HISTFILE variable is not set or is not
writable. A shell can access the commands of all interactive shells
which use the same named HISTFILE. The special command fc is used to
list or edit a portion of this file. The portion of the file to be
edited or listed can be selected by number or by giving the first
character or characters of the command. A single command or range of
commands can be specified. If you do not specify an editor program as an
argument to fc the value of the variable FCEDIT is used. If FCEDIT is
not defined /usr/bin/ed is used. The edited command(s) is printed and
re-executed upon leaving the editor. The editor name - is used to skip
the editing phase and to re-execute the command. In this case a
substitution variable of the form old=new can be used to modify the
command before execution. For example, if r is aliased to 'fc -e -',
typing `r bad=good c' re-executes the most recent command that starts
with the letter c, replacing the first occurrence of the string bad with
the string good.
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Inline Editing Option
Normally, each command line entered from a terminal device is simply
typed followed by a newline (`RETURN' or `LINE FEED'). If either the
emacs, or vi option is active, the user can edit the command line. To be
in either of these edit modes set the corresponding option. An editing
option is automatically selected each time the VISUAL or EDITOR variable
is assigned a value ending in either of these option names.
The editing features require that the user's terminal accept `RETURN' as
carriage return without line feed and that a space (` ') must overwrite
the current character on the screen.
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
is 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 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 character. For
example, M-f (pronounced Meta f) is entered by depressing ESC (ascii
\033) followed by `f'. (M-F would be the notation for ESC followed by
`SHIFT' (capital) `F'.)
All edit commands operate from any place on the line (not just at the
beginning). Neither the "RETURN" nor the "LINE FEED" key is entered
after edit commands except when noted.
^F Move cursor forward (right) one character.
M-f Move cursor forward one word. (The emacs editor's idea of a
word is a string of characters consisting of only letters,
digits and underscores.)
^B Move cursor backward (left) one character.
M-b Move cursor backward one word.
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^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 previous character.
^D Delete current character.
M-d Delete current word.
M-^H (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-DEL) Delete previous word (if your interrupt character is
^? (DEL, the default) then this command will not work).
^T Transpose current character with next character in emacs mode.
Transpose two previous characters in gmacs mode.
^C Capitalize current character.
M-c Capitalize current word.
M-l Change the current word to lower case.
^K Delete from the cursor to the end of the line. If preceded by
a numerical parameter whose value is less than the current
cursor position, then delete from given position up to the
cursor. If preceded by a numerical parameter whose value is
greater than the current cursor position, then delete from
cursor up to given cursor position.
^W Kill from the cursor to the mark.
M-p Push the region from the cursor to the mark on the stack.
kill (User defined kill character as defined by the stty command,
usually ^G or @.) Kill the entire current line. If two kill
characters are entered in succession, all kill characters from
then on cause a line feed (useful when using paper terminals).
^Y Restore last item removed from line. (Yank item back to the
line.)
^L Line feed and print current line.
^@ (Null character) Set mark.
M-space (Meta space) Set mark.
^J (New line) Execute the current line.
^M (Return) Execute the current line.
eof End-of-file character, normally ^D, is processed as an End-of-
file only if the current line is null.
^P Fetch previous command. Each time ^P is entered the previous
command back in time is accessed. Moves back one line when not
on the first line of a multi-line command.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command line. Each time ^N is entered the next
command line forward in time is accessed.
^Rstring Reverse search history for a previous command line containing
string. If a parameter of zero is given, the search is
forward. String is terminated by a "RETURN" or "NEW LINE". If
string is preceded by a ^, the matched line must begin with
string. If string is omitted, then the next command line
containing the most recent string is accessed. In this case a
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parameter of zero reverses the direction of the search.
^O Operate - Execute the current line and fetch the next line
relative to current line from the history file.
M-digits (Escape) Define numeric parameter, the digits are taken as a
parameter to the next command. The commands that accept a
parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-.,
M-^], M-_, M-b, M-c, M-d, M-f, M-h M-l and M-^H.
M-letter Soft-key - Your alias list is searched for an alias by the name
_letter and if an alias of this name is defined, its value will
be inserted on the input queue. The letter must not be one of
the above meta-functions. M-]letter Soft-key - Your alias list
is searched for an alias by the name __letter and if an alias
of this name is defined, its value will be inserted on the
input queue. The can be used to program functions keys on many
terminals.
M-. The last word of the previous command is inserted on the line.
If preceded by a numeric parameter, the value of this parameter
determines which word to insert rather than the last word.
M-_ Same as M-..
M-* Attempt file name generation on the current word. An asterisk
is appended if the word doesn't match any file or contain any
special pattern characters.
M-ESC File name completion. Replaces the current word with the
longest common prefix of all filenames matching the current
word with an asterisk appended. If the match is unique, a / is
appended if the file is a directory and a space is appended if
the file is not a directory.
M-= List files matching current word pattern if an asterisk were
appended.
^U Multiply parameter of next command by 4.
\ Escape next character. Editing characters, the user's erase,
kill and interrupt (normally ^?) characters may be entered in
a command line or in a search string if preceded by a \. The \
removes the next character's editing features (if any).
^V Display version of the shell.
M-# Insert a # at the beginning of the line and execute it. This
causes a comment to be inserted in the history file.
vi Editing Mode
There are two typing modes. Initially, when you enter a command you are
in the input mode. To edit, the user enters control mode by typing ESC
(\033), moves the cursor to the point needing correction, and 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 is echoed again if the speed is 1200 baud or
greater and it contains any control characters or less than one second
has elapsed since the prompt was printed. The ESC character terminates
canonical processing for the remainder of the command and the user can
modify the command line. This scheme has the advantages of canonical
processing with the type-ahead echoing of raw mode.
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If the option viraw is also set, the terminal always has canonical
processing disabled.
Input Edit Commands
By default the editor is in input mode.
erase (User defined erase character as defined by the stty command,
usually ^H or #.) Delete previous character.
^W Delete the previous blank separated word.
^D Terminate the shell.
^V Escape next character. Editing characters, the user's erase or
kill characters may be entered in a command line or in a search
string if preceded by a ^V. The ^V removes the next character's
editing features (if any).
\ Escape the next erase or kill character.
Motion Edit Commands
These 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.
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[count]; Repeats count times, the last single character find command,
f, F, t, or T.
[count], Reverses the last single character find command count times.
0 Cursor to start of line.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is entered the previous
command back in time is accessed.
[count]- Equivalent to k.
[count]j Fetch next command. Each time j is entered the next command
forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The default is the
least recent history command.
/string Search backward through history for a previous command
containing string. String is terminated by a "RETURN" or
"NEW LINE". If string is preceded by a ^, the matched line
must begin with string. If string is null the previous
string is used.
?string Same as / except that search is in the forward direction.
n Search for next match of the last pattern to / or ?
commands.
N Search for next match of the last pattern to / or ?, but in
reverse direction. Search history for the string entered by
the previous / command.
Text Modification Edit Commands
These commands 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 $a.
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[count]cmotion
c[count]motion Delete current character through the character that
motion would move the cursor to and enter input mode.
If motion is c, the entire line is deleted and input
mode entered.
C Delete the current character through the end of line and
enter input mode. Equivalent to c$.
S Equivalent to cc.
D Delete the current character through the end of line.
Equivalent to d$.
[count]dmotion
d[count]motion Delete current character through the character that
motion would move to. If motion is d, the entire line
is deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line.
Equivalent to 0i.
[count]P Place the previous text modification before the cursor.
[count]p Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen
with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the current
cursor position with c, and advance the cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]~ Invert the case of the count character(s) starting at
the current cursor position and advance the cursor.
[count]_ Causes the count word of the previous command to be
appended and input mode entered. The last word is used
if count is omitted.
* Causes an * to be appended to the current word and
filename generation attempted. If no match is found, it
rings the bell. Otherwise, the word is replaced by the
matching pattern and input mode is entered.
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\ Filename completion. Replaces the current word with the
longest common prefix of all filenames matching the
current word with an asterisk appended. If the match is
unique, a / is appended if the file is a directory and a
space is appended if the file is not a directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion
y[count]motion Yank current character through character that motion
would move the cursor to and puts them into the delete
buffer. The text and cursor are unchanged.
Y Yanks from current position to end of line. Equivalent
to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on the
line.
[count]v Returns the command fc -e ${VISUAL:-${EDITOR:-vi}} count
in the input buffer. If count is omitted, the current
line is used.
^L Line feed and print current line. Has effect only in
control mode.
^J (New line) Execute the current line, regardless of mode.
^M (Return) Execute the current line, regardless of mode.
# Sends the line after inserting a # in front of the line.
Useful for causing the current line to be inserted in
the history without being executed.
= List the filenames that match the current word if an
asterisk were appended it.
@letter Your alias list is searched for an alias by the name
_letter and if an alias of this name is defined, its
value is inserted on the input queue for processing.
Special Commands
The following simple-commands are executed in the shell process.
Input/output redirection is permitted. Unless otherwise indicated, the
output is written on file descriptor 1 and the exit status, when there is
no syntax error, is zero. Commands that are followed by one or two
asterisks, * or **, are treated specially in the following ways:
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1. Variable assignment lists preceding the command remain in effect
when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command followed 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 filename
generation are not performed.
: [ arg ... ] *
The command only expands parameters.
. file [ arg ... ] *
Read the complete file and execute the commands. The commands are
executed in the current shell environment. The search path
specified by PATH is used to find the directory containing file. If
any arguments arg are given, they become the positional parameters.
Otherwise the positional parameters are unchanged. The exit status
is the exit status of the last command executed.
alias [ -tx ] [ name[=value ] ] ... **
Alias with no arguments prints the list of aliases in the form
name=value on standard output. An alias is defined for each name
whose value is given. A trailing space in value causes the next
word to be checked for alias substitution. The -t flag is used to
set and list tracked aliases. The value of a tracked alias is the
full pathname corresponding to the given name. The value becomes
undefined when the value of PATH is reset but the aliases remain
tracked. Without the -t flag, for each name in the argument list
for which no value is given, the name and value of the alias is
printed. The -x flag is used to set or print exported aliases. An
exported alias is defined for scripts invoked by name. The exit
status is nonzero if a name is given, but no value, for which no
alias has been defined.
bg [ job... ]
This command is only on systems that support job control. Puts each
specified job into the background. The current job is put in the
background if job is not specified. See Jobs for a description of
the format of job.
break [ n ] *
Exit from the enclosing for, while, until or select loop, if any.
If n is specified, break n levels.
command [ -p ] command_name [ argument ... ]
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command [ -v | -V ] command_name
The command utility causes the shell to treat the arguments as a
simple command, suppressing the shell function lookup. If the
command_name is the same as the name of one of the special builtin
utilities, the special properties in the enumerated list at the
beginning of Special Commands section do not occur. In every other
respect, if command_name is not the name of a function, the effect
of command are the same as omitting command.
The -p option performs the search using a default value for PATH
that is guaranteed to find all of the standard utilities.
The -v option writes a string to standard output that indicates the
pathname or command that will be used by the shell, in the current
execution environment, to invoke command_name.
The -V option writes a string to standard output that indicates how
the name given in the command_name operand is interpreted by the
shell in the current shell execution environment. It indicates in
which of the following categories command_name falls and include the
information stated:
Utilities, regular builtin utilities, and any implementation-
provided functions that are found using the PATH variable are
identified as such and include the absolute pathname in the string.
Other shell functions are identified as functions.
Aliases are identified as aliases and their definitions are included
in the string.
Special builtin utilities are identified as special builtin
utilities.
Regular builtin utilities not associated with a PATH search are
identified as regular builtin utilities.
Shell reserved words are identified as reserved words.
continue [ n ] *
Resume the next iteration of the enclosing for, while, until or
select loop. If n is specified, resume at the n-th enclosing loop.
cd [ -LP ] arg
cd [ -LP ] 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
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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 arg
begins with a / 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.
If you specify -L, sh does not resolve symbolic links. This is the
default behavior.
If you specify -P, sh resolves all symbolic links.
If you specify both -L and -P, the last option specifies the
behavior.
The cd command may not be executed by restricted sh.
echo [ arg ... ]
See echo(1) for usage and description.
eval [ arg ... ] *
The arguments are read as input to the shell and the resulting
command(s) executed.
exec [ arg ... ] *
If arg is given, the command specified by the arguments is executed
in place of this shell without creating a new process. Input/output
arguments may appear and affect the current process. If no
arguments are given the effect of this command is to modify file
descriptors as prescribed by the input/output redirection list. In
this case, any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking another program.
exit [ n ] *
Causes the shell to exit with the exit status specified by n. If n
is omitted the exit status is that of the last command executed. An
end-of-file also causes 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.
export -p **
When -p is specified, export writes to the standard the output names
and values of all exported variables, in the following format:
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sh(1)sh(1)
"export %s=%s\n",< name >, < value >
The -p option allows portable access to the values that can be saved
and later restored using, for instance, a dot script.
The shell formats the output, including the proper use of quoting,
so that it is suitable for reinput to the shell as commands that
achieve the same exporting results.
fc [ -e ename ] [ -nlr ] [ first [ last ] ]
fc -e - [ old=new ] [ command ]
fc -s [ old=new ] [ first ]
In the first form, a range of commands from first to last is
selected from the last HISTSIZE commands that were typed at the
terminal. The arguments first and last may be specified as a
[+]number or as a string. A string is used to locate the most
recent command starting with the given string. A negative number is
used as an offset to the current command number. If the flag -l, is
selected, the commands are listed on standard output. Otherwise,
the editor program ename is invoked on a file containing these
keyboard commands. If ename is not supplied, the value of the
variable FCEDIT (default /usr/bin/ed) is used as the editor. When
editing is complete, the edited command(s) is executed. If last is
not specified it is 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.
In the third form the command is re-executed after the substitution
old=new is performed without invoking an editor.
fg [ job... ]
This command is only on systems that support job control. Each job
specified is brought to the foreground. Otherwise, the current job
is brought into the foreground. See Jobs for a description of the
format of job.
getopts optstring name [ arg ... ]
Checks arg for legal options. If arg is omitted, the positional
parameters are used. An option argument begins with a + or a -. An
option not beginning with + or - or the argument -- ends the
options. optstring contains the letters that getopts recognizes.
If a letter is followed by a :, that option is expected to have an
argument. The options can be separated from the argument by blanks.
getopts places the next option letter it finds inside variable name
each time it is invoked with a + prepended when arg begins with a +.
The index of the next arg is stored in OPTIND. The option argument,
if any, gets stored in OPTARG. Whenever the shell is invoked,
OPTIND is initialized to 1.
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sh(1)sh(1)
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 [ -sig ] -1
kill -s signal_name job ...
kill -l [ exit_status ]
Sends either the TERM (terminate) signal or the specified signal to
the specified jobs or processes. In the second form, the TERM
(terminate) or specified signal is sent to all processes owned by
the user. 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), the job or
process is sent a CONT (continue) signal if it is stopped. The
argument job can the process id of a process that is not a member of
one of the active jobs. See Jobs for a description of the format of
job. In the fourth form, kill -l, the signal numbers and names are
listed. If an exit_status operand is given and it is the unsigned
decimal integer value of a signal number, the signal_name (the
specification-defined symbolic constant name without the ``SIG''
prefix) corresponding to that signal is written.
let arg ...
Each arg is a separate arithmetic expression to be evaluated. See
Arithmetic Evaluation above, for a description of arithmetic
expression evaluation.
The exit status is 0 if the value of the last expression is nonzero,
and 1 otherwise.
limit [ -h ] resource maximum-use
This is the Bourne shell version included for backward
compatibility. Limits the consumption by the current process and
each process it creates to not individually exceed maximum-use on
the specified resource. If no maximum-use is given, then the
current limit is printed; if no resource is given, then all
limitations are given. If the -h flag is given, the hard limits are
used instead of the current limits. The hard limits impose a
ceiling on the values of the current limits. Only the superuser can
raise the hard limits, but a user can lower or raise the current
limits within the legal range.
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sh(1)sh(1)
Resources controllable currently include cputime, the maximum number
of cpu-seconds to be used by each process, filesize, the largest
single file that can be created, datasize, the maximum growth of the
data region via sbrk(2) beyond the end of the program text,
stacksize, the maximum size of the automatically-extended stack
region, coredumpsize, the size of the largest core dump created,
memoryuse, the maximum amount of physical memory a process can have
allocated to it at a given time, descriptors, the maximum number of
open files, vmemory, the maximum total virtual size of the process,
including text, data, heap, shared memory, mapped files, stack, and
so on, and threads, the maximum number of pthreads(5) the process
may create.
The maximum-use can be given as a (floating point or integer) number
followed by a scale factor. For all limits other than cputime,
descriptors and threads the default scale is k or kilobytes (1024
bytes); a scale factor of m or megabytes can also be used. For
cputime the default scaling is seconds, while m for minutes or h for
hours, or a time of the form mm:ss giving minutes and seconds can be
used.
For both resource names and scale factors, unambiguous prefixes of
the names suffice.
newgrp [ -l ] [ arg ] *
newgrp [ - ] [ arg ] *
Equivalent to exec /usr/bin/newgrp arg. The -l (ell) or the -
option change the environment to what would be expected if the user
actually logged in again.
print [ -Rnprsu[n ] ] [ arg ... ]
The shell output mechanism. With no flags or with flag - or -- the
arguments are printed on standard output as described by echo(1).
In raw mode, -R or -r, the escape conventions of echo are ignored.
The -R option prints 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 is
placed. The default is 1. If the flag -n is used, no newline is
added to the output.
pwd [ -LP ]
This is equivalent to print -r - $PWD if you have not changed PWD.
If you specify -L, sh does not resolve symbolic links. This is the
default behavior.
If you specify -P, sh resolves all symbolic links.
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sh(1)sh(1)
If you specify both -L and -P, the last option specifies the
behavior.
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 is 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 REPLY is used as the default name. The exit status
is 0 unless an end-of-file is encountered. An end-of-file with the
-p option causes cleanup for this process so that another can be
spawned. If the first argument contains a ?, the remainder of this
word is used as a prompt on standard error when the shell is
interactive. The exit status is 0 unless an end-of-file is
encountered.
readonly [ name[=value] ] ... **
The given names are marked readonly and these names cannot be
changed by subsequent assignment.
readonly -p **
When -p is specified, readonly writes to the standard the output
names and values of all read-only variables, in the following
format:
"readonly %s=%s\n",< name >, < value >
The -p option allows portable access to the values that can be saved
and later restored using, for instance, a dot script.
The shell formats the output, including the proper use of quoting,
so that it is suitable for reinput to the shell as commands that
achieve the same attribute-setting results.
return [ n ] *
Causes a shell function to return to the invoking script with the
return status specified by n. If n is omitted the return status is
that of the last command executed. If return is invoked while not
in a function or a . script, it is the same as an exit.
set [ -abCefhkmnpstuvx ] [ -o option ] [ -A name ] [ arg ... ] *
The flags for this command have meaning as follows:
Page 32
sh(1)sh(1)-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.
-b Cause the shell to notify the user asynchronously of background
job completions. When the shell notifies the user a job has
been completed, it may remove the job's process ID from the
list of those known in the current shell execution environment.
Asynchronous notification is not enabled by default.
-C (Upper-case C) Prevent existing files from being overwritten by
the shell's > redirection operator. The >| redirection
operator overrides this noclobber option for an individual
file.
-e If a command has a nonzero exit status, execute the ERR trap,
if set, and exit. This mode is disabled while reading
profiles.
-f Disables filename 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 run in a separate process group and a line
prints upon completion. The exit status of background jobs is
reported in a completion message. On systems with job control,
this flag is turned on automatically for interactive shells.
-n Read commands and check them for syntax errors, but do not
execute them. Ignored for interactive shells.
-o The following argument can be one of the following option
names:
allexport Same as -a.
errexit Same as -e.
bgnice All background jobs are run at a lower priority.
This is the default mode.
emacs Puts you in an emacs style in-line editor for
command entry.
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ignoreeof The shell does not exit on end-of-file. The
command exit must be used.
keyword Same as -k.
markdirs All directory names resulting from filename
generation have a trailing / appended.
monitor Same as -m.
noclobber Same as -C.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in history file.
notify Same as -b.
nounset Same as -u.
privileged Same as -p.
verbose Same as -v.
trackall Same as -h.
vi Puts you in insert mode of a vi style inline
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 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 Sort the positional parameters lexicographically.
-t Exit after reading and executing one command.
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sh(1)sh(1)-u Treat unset parameters as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
- Turns off -x and -v flags and stops examining arguments for
flags.
-- Do not change any of the flags; useful in setting $1 to a value
beginning with -. If no arguments follow this flag 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 the names and values
of all variables are printed on the standard output.
shift [ n ] *
The positional parameters from $n+1 ... are renamed $1 ..., default
n is 1. The parameter n can be any arithmetic expression that
evaluates to a non-negative number less than or equal to $#.
times *
Print the accumulated user and system times for the shell and for
processes run from the shell.
trap [ arg ] [ sig ] ... *
arg is a command to be read and executed when the shell receives
signal(s) sig. (Note that arg is scanned once when the trap is set
and once when the trap is taken.) Each sig can be given as a number
or as the name of the signal. Trap commands are executed in order
of signal number. Any attempt to set a trap on a signal that was
ignored on entry to the current shell is ineffective. If arg is
omitted or is -, all trap(s) 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, arg is executed whenever a
command has a nonzero exit status. sig is DEBUG arg is executed
after each command. If sig is 0 or EXIT and the trap statement is
executed inside the body of a function, the command arg is executed
after the function completes. If sig is 0 or EXIT for a trap set
outside any function the command arg is executed on exit from the
shell. The trap command with no arguments prints a list of commands
associated with each signal number.
typeset [ _HLRZfilrtux[n] ] [ name[=value ] ] ... **
Sets attributes and values for shell variables. When invoked inside
a function, a new instance of the variable name is created. The
parameter value and type are restored when the function completes.
The following list of attributes may be specified:
Page 35
sh(1)sh(1)-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
nonzero 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 nonzero 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 nonzero it defines the width of the field, otherwise it
is determined by the width of the value of first assignment.
-f The names refer to function names rather than variable names.
No assignments can be made and the only other valid flags are
-t, -u and -x. The flag -t turns on execution tracing for this
function. The flag -u causes this function to be marked
undefined. The FPATH variable is 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
nonzero 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.
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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 | cdfnstvmp] ]
ulimit [ -[HS][c | d | f | n | s | t | v | m | p] ] limit
ulimit prints or sets hard or soft resource limits. These limits
are described in getrlimit(2).
If limit is not present, ulimit prints the specified limits. Any
number of limits may be printed at one time. The -a option prints
all limits.
If limit is present, ulimit sets the specified limit to limit. The
string unlimited requests the largest valid limit. Limits may be
set for only one resource at a time. Any user may set a soft limit
to any value below the hard limit. Any user may lower a hard limit.
Only a privileged user may raise a hard limit; see su(1M).
The -H option specifies a hard limit. The -S option specifies a
soft limit. If neither option is specified, ulimit sets both limits
and prints the soft limit.
The following options specify the resource whose limits are to be
printed or set. If no option is specified, the file size limit is
printed or set.
-c maximum core file size (in 512-byte blocks)
-d maximum size of data segment or heap (in kbytes)
-f maximum file size (in 512-byte blocks)
-n maximum file descriptor plus 1
-s maximum size of stack segment (in kbytes). Note that if this
is set too high, sproc(2) may fail.
-t maximum CPU time (in seconds)
-v maximum size of virtual memory (in kbytes)
-m maximum size of resident memory (in kbytes)
-p maximum number of pthreads(5) that process may create.
If no option is given, -f is assumed.
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umask [ -S ][ 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. If -S is specified, the symbolic output is in the
following format:
"u=%s,g=%s,o=%s\n", owner, group, other
where the three values are permissions combinations of the letters
from the set {r,w,x}.
unalias name ...
unalias -a
The variables given by the list of names are removed from the alias
list. In the second form, all alias definitions are removed from
the current shell execution environment.
unlimit [ -h ] resource
This is the Bourne shell version included for backward
compatibility. Removes the limitation on resource. If no resource
is specified, then all resource limitations are removed. If -h is
given, the corresponding hard limits are removed. Only the
superuser can do this. (See limit above)
unset [ -fv ] name ... *
The variables given by the list of names are unassigned, i. e.,
their values and attributes are erased. Read-only variables cannot
be unset. If the flag, -v, is set, the names refer to variable
names. This is the default when no options are specified. If the
flag, -f, is set, the names refer to function names. Unsetting
ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT,
and _ causes removes their special meaning even if they are
subsequently assigned to. In some shell invocations, unsetting
variables not previously set or null returns a value of 0. (See the
COMPATIBILITY ISSUES section at the end of this document.)
wait [ job ] *
Wait for the specified job and report its termination status. If
job is not given 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 is interpreted if used as a command
name.
-v produces a more verbose report.
Page 38
sh(1)sh(1)-p does a path search for name even if name is an alias, a
function, or a reserved word.
Invocation
If the shell is invoked by exec(2), and the first character of argument
zero ($0) is -, 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 filenamed 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, 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 are ignored. Commands
are read as described below; the following flags are interpreted by the
shell when it is invoked:
-c string If the -c flag is present commands are read from string.
-s If the -s flag is present or if no arguments remain, 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)) this shell
is interactive. In this case TERM is ignored (so that kill 0
does not kill an interactive shell) and INTR is caught and
ignored (so that wait is interruptible). In all cases, QUIT
is ignored by the shell.
-r If the -r flag is present the shell is a restricted shell.
The remaining flags and arguments are described under the set command
above.
Restricted sh Only
The restricted sh is used to set up login names and execution
environments whose capabilities are more controlled than those of the
standard shell. The actions of the restricted sh are identical to those
of sh, except that the following are disallowed:
Changing directory [see cd(1)]
Setting the value of SHELL, ENV, or PATH
Specifying path or command names containing /
Redirecting output (>, >|, <>, and >>)
The restrictions above are enforced after .profile and the ENV files are
interpreted.
When a command to be executed is found to be a shell procedure, the
restricted sh invokes sh to execute it. Thus, it is possible to provide
to the end-user shell procedures that have access to the full power of
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sh(1)sh(1)
the standard shell, while imposing a limited menu of commands; this
scheme assumes that the end-user does not have write and execute
permissions in the same directory.
The net effect of these rules is that the writer of the .profile has
complete control over user actions, by performing guaranteed setup
actions and leaving the user in an appropriate directory (probably not
the login directory).
The system administrator often sets up a directory of commands (that is,
/usr/rbin) that can be safely invoked by the restricted sh.
WARNING: Since the restricted sh depends on .profile to set up
restrictions, and .profile is only interpreted by login shells, allowing
a restricted sh user to access the system in a manor that does not invoke
a login shell will allow the user to bypass these restrictions. An
example of this type of access is remote shell (See rsh_bsd(1C)).
EXIT STATUS
Errors detected by the shell, such as syntax errors, cause the shell to
return a nonzero 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, 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, the line
number is also printed in square brackets ([]) after the command or
function name.
If a command is not found, the exit status is 127. If the command name
is found, but it is not an executable utility, the exit status is 126.
Applications that invoke utilities without using the shell should use
these exit status values to report similar errors.
If a command fails during word expansion or redirection, its exit status
is greater than zero.
Internally, for purposes of deciding if a command exits with a nonzero
exit status, the shell recognizes the entire status value retrieved for
the command by the equivalent of the wait() function WEXITSTATUS macro.
When reporting the exit status with the special parameter ?, the shell
reports the full eight bits of exit status available. The exit status of
a command that terminated because it received a signal is reported as
greater than 128.
FILES
/etc/passwd
/etc/profile
/etc/suid_profile
$HOME/.profile
/tmp/sh*
/dev/null
Page 40
sh(1)sh(1)SEE ALSOemacs(1), cat(1), cd(1), chmod(1), cut(1), echo(1), env(1), newgrp(1M),
paste(1), stty(1), test(1), umask(1), vi(1), dup(2), exec(2), fork(2),
ioctl(2), lseek(2), pipe(2), signal(2), ulimit(2), umask(2), wait(2),
rand(3C), a.out(4), profile(4), environ(5).
Morris I. Bolsky and David G. Korn, The KornShell Command and Programming
Language, Prentice Hall, 1989
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 continues 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 builtin command within a compound command causes the whole
command to disappear from the history file.
The builtin command . file reads the whole file before any commands are
executed. Therefore, alias and unalias commands in the file do 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.
Prior to IRIX Release 5.0, the rsh command invoked the restricted shell.
This restricted shell command is /usr/lib/rsh and it can be executed by
using the full pathname. Beginning with IRIX Release 5.0, the rsh
command is the remote shell. See rsh_bsd(1C).
Sometimes, particularly when using wildcards, the shell will fail to
execute a command, and complain with the message
arg list too long
This can often be avoided by using multiple commands, the xargs(1)
command, or by increasing the ncargs kernel parameter with the
systune(1m) command.
COMPATIBILITY ISSUES
To retain some backward compatibility to the Bourne shell, certain Korn
shell features are controlled by how the shell is invoked and/or the
current value of the environment variable _XPG.
When the shell is invoked as "sh", the following features are performed
only when the current value of the _XPG variable is equal to 1 (one):
- command substitution of the form "$( command )"
- arithmetic expression of the form "$(( expression ))"
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sh(1)sh(1)
- tilde expansion of pathnames
- unsetting variables, not previously set or null, returns 0
When the shell is invoked as "sh" and the current value of the _XPG
environment variable is not equal to 1 (one), the special positional
parameter $0, within a function call, is the name of the function.
Otherwise, it is the name of the invoking shell script.
When the shell is not invoked as "sh" and the real and effective uid and
gid differ, the effective uid and gid are set to the real uid and gid.
With all invocations of the shell, when the current value of the _XPG
environment variable is equal to 1 (one), the -n option of the builtin
echo command does not suppress the terminating newline and is treated as
part of the output string.
Additional incompatibilities are listed below and can be found in the
Appendix of the "The Kornshell Command and Programming Language" (Bolsky
& Korn; Prentice Hall)
The Korn shell is more restrictive with field comparisons in the builtin
test command:
[ "10240 filename" -ge 10240 ]
is accepted by the Bourne shell whereas the Korn shell gives a syntax
error.
The Korn shell kill builtin command now handles the special process
number (-1) for all process owned by the user. (See the Special Commands
section.)
The false command is a builtin for the Korn shell and cannot be defined
as a function.
The chdir is a builtin alias to the cd command. When shell is invoked as
"ksh", this alias is removed allowing chdir to be defined as a function.
When shell is invoked as "sh", this can also be accomplished by
unaliasing chdir and then defining it as a function.
Some Korn shell internal variables are typeset as integers and setting
them to non-numeric values will cause "bad number" error messages. They
include ERRNO, LINENO, MAILCHECK, OPTIND, PPID, RANDOM, SECONDS and
TMOUT.
The Korn shell evaluates variable assignment lists before I/O redirection
unlike the Bourne shell in which order does not matter.
The Bourne shell (bsh) has been modified to allow fullpath calls of
Bourne shell builtins using the builtin name POSIX links to
/sbin/builtin_exec.
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sh(1)sh(1)INTERNATIONALIZATION
The shell accepts multibyte input for command line args, file names,
environment variable names and values, variable arrays, function names,
history files and shell scripts. Multibyte sequences accepted for the
isphonogram() and isideogram() subroutines are also allowed.
Note: The emacs line editing feature is currently supported only with the
default C/POSIX locale.
Note: Changing the LANG value during a shell session can produce
undefined results when accessing e.g. variables created under a different
locale.
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