Linux Script Variables
When variables are used they are referred to with the $ symbol in front of them. There are several useful variables available in the shell program. Here are a few:
- $$ = The PID number of the process executing the shell.
- $? = Exit status variable.
- $0 = The name of the command you used to call a program.
- $1 = The first argument on the command line.
- $2 = The second argument on the command line.
- $n = The nth argument on the command line.
- $* = All the arguments on the command line.
- $# The number of command line arguments.
The "shift" command can be used to shift command line arguments to the left, ie $1 becomes the value of $2, $3 shifts into $2, etc. The command, "shift 2" will shift 2 places meaning the new value of $1 will be the old value of $3 and so forth.
Variables are assigned in a script program as follows:
They are used in this manner:
while [ $DONE = no ]