Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
rxvt
bash$ echo $LOGNAME
bozo
bash$ echo $SHELL
/bin/tcsh
bash$ echo $TERM
rxvt
Positional Parameters
$0, $1, $2, etc.
positional parameters, passed from command line to script, passed to a function, or set to a variable
(see Example 4−5 and Example 11−13)
$#
number of command line arguments [20] or positional parameters (see Example 34−2)
$*
All of the positional parameters, seen as a single word
$@
Same as $*, but each parameter is a quoted string, that is, the parameters are passed on intact, without
interpretation or expansion. This means, among other things, that each parameter in the argument list
is seen as a separate word.
Example 9−6. arglist: Listing arguments with $* and $@
#!/bin/bash
# Invoke this script with several arguments, such as "one two three".
E_BADARGS=65
if [ ! −n "$1" ]
then
echo "Usage: `basename $0` argument1 argument2 etc."
exit $E_BADARGS
fi
echo
index=1
echo "Listing args with \"\$*\":"
for arg in "$*" # Doesn't work properly if "$*" isn't quoted.
do
echo "Arg #$index = $arg"
let "index+=1"
done
# $* sees all arguments as single word.
echo "Entire arg list seen as single word."
echo
index=1
echo "Listing args with \"\$@\":"
for arg in "$@"
do
Chapter 9. Variables Revisited 74