| ${Parameter}
| The shell reads all the characters from the ${ to the matching
} as part of the same word, even if that word contains braces or
metacharacters. The value, if any, of the specified parameter is
substituted. The braces are required when the Parameter
parameter is followed by a letter, digit, or underscore that is not to be
interpreted as part of its name, or when a named parameter is
subscripted.
If the specified parameter contains one
or more digits, it is a positional parameter. A positional
parameter of more than one digit must be enclosed in braces. If the
value of the variable is an * or an @), each positional
parameter, starting with $1, is substituted (separated by a field
separator character). If an array identifier with a subscript
* or an @ is used, then the value for each of the
elements (separated by a field separator character) is substituted.
|
| ${#Parameter}
| If the value of the Parameter parameter is an * or an @, the
number of positional parameters is substituted. Otherwise, the length
specified by the Parameter parameter is substituted.
|
| ${#Identifier[*]}
| The number of elements in the array specified by the
Identifier parameter is substituted.
|
| ${Parameter:-Word}
| If the Parameter parameter is set and is not null, then its
value is substituted; otherwise, the value of the Word
parameter is substituted.
|
| ${Parameter:=Word}
| If the Parameter parameter is not set or is null, then it is
set to the value of the Word parameter. Positional
parameters cannot be assigned in this way.
|
| ${Parameter:?Word}
| If the Parameter parameter is set and is not null, then
substitute its value. Otherwise, print the value of the Word
variable and exit from the shell. If the Word variable is
omitted, then a standard message is printed.
|
| ${Parameter:+Word}
| If the Parameter parameter is set and is not null, then
substitute the value of the Word variable. Otherwise,
substitute nothing.
|
| ${Parameter#Pattern}
| ${Parameter##Pattern}
| If the specified shell Pattern parameter matches the beginning
of the value of the Parameter parameter, then the value of this
substitution is the value of the Parameter parameter with the
matched portion deleted. Otherwise, the value of the
Parameter parameter is substituted. In the first form, the
smallest matching pattern is deleted. In the second form, the largest
matching pattern is deleted.
|
| ${Parameter%Pattern}
| ${Parameter%%Pattern}
| If the specified shell Pattern matches the end of the value of
the Parameter variable, then the value of this substitution is the
value of the Parameter variable with the matched part deleted;
otherwise, substitute the value of the Parameter variable.
In the first form, the smallest matching pattern is deleted; in the
second form, the largest matching pattern is deleted.
In the previous expressions, the Word variable is not evaluated
unless it is to be used as the substituted string. Thus, in the
following example the pwd command is executed only if the
-d flag is not set or is null:
echo ${d:-$(pwd)}
|
| @
| Expands the positional parameters, beginning with $1.
Each parameter is separated by a space.
If you place " around
$@, the shell considers each positional parameter a separate
string. If no positional parameters exist, the shell expands the
statement to an unquoted null string.
|
| *
| Expands the positional parameters, beginning with $1.
The shell separates each parameter with the first character of the IFS parameter value.
If you place " around
$*, the shell includes the positional parameter values in double
quotation marks. Each value is separated by the first character of the
IFS parameter.
|
| #
| Specifies the number (in decimals) of positional parameters passed to the
shell, not counting the name of the shell procedure itself. The
$# parameter thus yields the number of the highest-numbered
positional parameter that is set. One of the primary uses of this
parameter is to check for the presence of the required number of
arguments.
|
| -
| Supplies flags to the shell on invocation or with the set
command.
|
| ?
| Specifies the exit value of the last command executed. Its value
is a decimal string. Most commands return 0 to indicate successful
completion. The shell itself returns the current value of the
$? parameter as its exit value.
|
| $
| Identifies the process number of this shell. Because process
numbers are unique among all existing processes, this string of up to 5 digits
is often used to generate unique names for temporary files.
The following example illustrates the recommended practice of creating
temporary files in a directory used only for that purpose:
temp=$HOME/temp/$$
ls >$temp
.
.
.
rm $temp
|
| !
| Specifies the process number of the last background command
invoked.
|
| zero (0)
| Expands to the name of the shell or shell script.
|
| underscore (_)
| Indicates initially the absolute path name 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 that are asynchronous. This parameter is also used to hold the
name of the matching MAIL file when checking for mail.
|
| ERRNO
| Specifies a value that is set by the most recently failed
subroutine. This value is system-dependent and is intended for
debugging purposes.
|
| LINENO
| Specifies the line number of the current line within the script or
function being executed.
|
| OLDPWD
| Indicates the previous working directory set by the cd
command.
|
| OPTARG
| Specifies the value of the last option argument processed by the
getopts regular built-in command.
|
| OPTIND
| Specifies index of the last option argument processed by the
getopts regular built-in command.
|
| PPID
| Identifies the process number of the parent of the shell.
|
| PWD
| Indicates the present working directory set by the cd
command.
|
| RANDOM
| Generates a random integer, uniformly distributed between 0 and
32767. The sequence of random numbers can be initialized by assigning a
numeric value to the RANDOM variable.
|
| REPLY
| Set by the select statement and by the read regular
built-in command when no arguments are supplied.
|
| SECONDS
| Specifies the number of seconds since shell invocation is
returned. If this variable is assigned a value, then the value returned
upon reference will be the value that was assigned plus the number of seconds
since the assignment.
|
| CDPATH
| Indicates the search path for the cd (change directory)
command.
|
| COLUMNS
| Defines the width of the edit window for the shell edit modes and for
printing select lists.
|
| EDITOR
| If the value of this parameter ends in emacs, gmacs, or vi, and the
VISUAL variable is not set with the set special built-in
command, then the corresponding option is turned on.
|
| ENV
| If this variable is set, then parameter substitution is performed on the
value to generate the path name of the script that will be executed when the
shell is invoked. This file is typically used for alias and function
definitions.
|
| FCEDIT
| Specifies the default editor name for the fc regular built-in
command.
|
| FPATH
| Specifies the search path for function definitions. This path is
searched when a function with the -u flag is referenced and when a
command is not found. If an executable file is found, then it is read
and executed in the current environment.
|
| HISTFILE
| If this variable is set when the shell is invoked, then the value is the
path name of the file that will be used to store the command history.
|
| HISTSIZE
| If this variable is set when the shell is invoked, then the number of
previously entered commands that are accessible by this shell will be greater
than or equal to this number. The default is 128.
|
| HOME
| Indicates the name of your login directory, which becomes the current
directory upon completion of a login. The login program
initializes this variable. The cd command uses the value of
the $HOME parameter as its default value. Using this
variable rather than an explicit path name in a shell procedure allows the
procedure to be run from a different directory without alterations.
|
| IFS
| Specifies internal field separators (normally space, tab, and new line)
used to separate command words that result from command or parameter
substitution and for separating words with the regular built-in command
read. The first character of the IFS parameter is
used to separate arguments for the $* substitution.
|
| LANG
| Provides a default value for the LC_* variables.
|
| LC_ALL
| Overrides the value of the LANG and LC_*
variables.
|
| LC_COLLATE
| Determines the behavior of range expression within pattern
matching.
|
| LC_CTYPE
| Defines character classification, case conversion, and other character
attributes.
|
| LC_MESSAGES
| Determines the language in which messages are written.
|
| LINES
| Determines the column length for printing select lists. Select
lists print vertically until about two-thirds of lines specified by the
LINES variable are filled.
|
| MAIL
| Specifies the file path name used by the mail system to detect the
arrival of new mail. If this variable is set to the name of a mail file
and the MAILPATH variable is not set, then the shell informs the
user of new mail in the specified file.
|
| MAILCHECK
| 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
| Specifies a list of file names separated by colons. If this
variable is set, then the shell informs the user of any modifications to the
specified files that have occurred during the period, in seconds, specified by
the MAILCHECK variable. Each file name can be followed by a
? and a message that will be printed. The message will
undergo variable substitution with the $_ variable
defined as the name of the file that has changed. The default message
is you have mail in $_.
|
| NLSPATH
| Determines the location of message catalogs for the processing of
LC_MESSAGES.
|
| PATH
| Indicates the search path for commands, which is an ordered list of
directory path names separated by colons. The shell searches these
directories in the specified order when it looks for commands. A null
string anywhere in the list represents the current directory.
|
| PS1
| Specifies the string to be used as the primary system prompt. The
value of this parameter is expanded for parameter substitution to define the
primary prompt string, which is a $ by default. The
! character in the primary prompt string is replaced by the command
number.
|
| PS2
| Specifies the value of the secondary prompt string, which is a
> by default.
|
| PS3
| Specifies the value of the selection prompt string used within a
select loop, which is #? 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 a +.
|
| SHELL
| Specifies the path name of the shell, which is kept in the
environment.
|
| TMOUT
| Specifies the number of seconds a shell waits inactive before
exiting. If the TMOUT variable is set to a value greater
than zero (0), the shell exits 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 boundary that cannot be
exceeded for this value.)
Note: After the timeout period has expired, there is a
60-second pause before the shell exits.
|
| VISUAL
| If the value of this variable ends in emacs, gmacs, or vi, then the
corresponding option is turned on.
|