Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
Example 11−13. Using set with positional parameters
#!/bin/bash
# script "set−test"
# Invoke this script with three command line parameters,
# for example, "./set−test one two three".
echo
echo "Positional parameters before set \`uname −a\` :"
echo "Command−line argument #1 = $1"
echo "Command−line argument #2 = $2"
echo "Command−line argument #3 = $3"
set `uname −a` # Sets the positional parameters to the output
# of the command `uname −a`
echo $_ # unknown
# Flags set in script.
echo "Positional parameters after set \`uname −a\` :"
# $1, $2, $3, etc. reinitialized to result of `uname −a`
echo "Field #1 of 'uname −a' = $1"
echo "Field #2 of 'uname −a' = $2"
echo "Field #3 of 'uname −a' = $3"
echo −−−
echo $_ # −−−
echo
exit 0
Invoking set without any options or arguments simply lists all the environmental and other variables
that have been initialized.
bash$ set
AUTHORCOPY=/home/bozo/posts
BASH=/bin/bash
BASH_VERSION=$'2.05.8(1)−release'
...
XAUTHORITY=/home/bozo/.Xauthority
_=/etc/bashrc
variable22=abc
variable23=xzy
Using set with the −− option explicitly assigns the contents of a variable to the positional parameters.
When no variable follows the −−, it unsets the positional parameters.
Example 11−14. Reassigning the positional parameters
#!/bin/bash
variable="one two three four five"
set −− $variable
# Sets positional parameters to the contents of "$variable".
Chapter 11. Internal Commands and Builtins 135