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Accessing The Command Line
The shell provides a set of variables called positional parameters that contain the individ- ual words on the command line. The variables are named 0 through 9. They can be demonstrated this way:
#!/bin/bash
# posit-param: script to view command line parameters echo "
\$0 = $0
\$1 = $1
\$2 = $2
\$3 = $3
\$4 = $4
\$5 = $5
\$6 = $6
\$7 = $7
\$8 = $8
\$9 = $9 "
A very simple script that displays the values of the variables $0-$9. When executed with no command line arguments, the result is this:
[me@linuxbox ~]$ posit-param
$0 = /home/me/bin/posit-param
[me@linuxbox ~]$ posit-param
$0 = /home/me/bin/posit-param
$1 =
$2 =
$3 =
$4 =
$5 =
$6 =
$7 =
$8 =
$9 =
$1 =
$2 =
$3 =
$4 =
$5 =
$6 =
$7 =
$8 =
$9 =
Even when no arguments are provided, $0 will always contain the first item appearing on the command line, which is the pathname of the program being executed. When argu- ments are provided, we see these results:
[me@linuxbox ~]$ posit-param a b c d
$0 | = | /home/me/bin/posit-param |
$1 | = | a |
$2 | = | b |
$3 | = | c |
$4 | = | d |
$5 | = | |
$6 | = | |
$7 | = | |
$8 | = | |
$9 | = |
Note: You can actually access more than nine parameters using parameter expan- sion. To specify a number greater than nine, surround the number in braces. For ex- ample ${10}, ${55}, ${211}, and so on.