Книга: Fedora™ Unleashed, 2008 edition

Built-In Variables

Built-In Variables

Built-in variables are special variables provided to the shell by Linux that can be used to make decisions within a shell program. You cannot modify the values of these variables within the shell program.

Some of these variables are the following:

? $# — Number of positional parameters passed to the shell program

? $? — Completion code of the last command or shell program executed within the shell program (returned value)

? $0 — The name of the shell program

? $* — A single string of all arguments passed at the time of invocation of the shell program

To show these built-in variables in use, here is a sample program called mypgm2:

#!/bin/sh
#my test program
echo "Number of parameters is $#"
echo "Program name is $0"
echo "Parameters as a single string is $*"

If you execute mypgm2 from the command line in bash as follows

$ bash mypgm2 Andrew Hudson

you get the following result:

Number of parameters is 2
Program name is mypgm2
Parameters as a single string is Sanjiv Guha

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