Below are the special shell variables. These are important
to know for everyone, especially who is willing to learn shell scripting. Hope the list helps.
|
Name
|
Description
|
|
$1
- $9
|
These
variables are referring the parameters passed to command or script. $1 refers
to the first argument and $2 refers second and so on.
|
|
$0
|
The
name of the command or script currently being executed.
|
|
$#
|
The
number of arguments passed to the command/script or invocation of the shell.
|
|
$?
|
The
exit status of the last command executed is given as a decimal string. When a command completes successfully, it
returns the exit status of 0 (zero), otherwise it returns a non-zero exit
status.
|
|
$$
|
The
process number of the currently executing command or script. - Useful for
including in filenames, to make them unique.
|
|
$!
|
The
process ID of the last command runs in the background.
|
|
$-
|
The
current options supplied to the command or script.
|
|
$*
|
A
string containing all the arguments passed to the command/script or shell,
starting at $1. When quoted, "$*" is a single word, comprising all
the arguments to the shell, joined together with spaces. For example ‘a b' c becomes
"a b c".
|
|
$@
|
Same
as above, except when quoted. When quoted, "$@" is identical to the
arguments received by the shell, the resulting list of words completely match
what was given to the shell. For example '1 2' 3 becomes "1 2"
"3"
|
Apart from these, there are some standard variables which are set through .profile or .bashrc. Try "env" command to view all of them.