Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
echo "Arg #$index = $arg"
let "index+=1"
done
# $@ sees arguments as separate words.
echo "Arg list seen as separate words."
echo
exit 0
Following a shift, the $@ holds the remaining command−line parameters, lacking the previous $1,
which was lost.
#!/bin/bash
# Invoke with ./scriptname 1 2 3 4 5
echo "$@" # 1 2 3 4 5
shift
echo "$@" # 2 3 4 5
shift
echo "$@" # 3 4 5
# Each "shift" loses parameter $1.
# "$@" then contains the remaining parameters.
The $@ special parameter finds use as a tool for filtering input into shell scripts. The cat "$@"
construction accepts input to a script either from stdin or from files given as parameters to the
script. See Example 12−17 and Example 12−18.
The $* and $@ parameters sometimes display inconsistent and puzzling behavior,
depending on the setting of $IFS.
Example 9−7. Inconsistent $* and $@ behavior
#!/bin/bash
# Erratic behavior of the "$*" and "$@" internal Bash variables,
#+ depending on whether they are quoted or not.
# Inconsistent handling of word splitting and linefeeds.
set −− "First one" "second" "third:one" "" "Fifth: :one"
# Setting the script arguments, $1, $2, etc.
echo
echo 'IFS unchanged, using "$*"'
c=0
for i in "$*"
# quoted
do echo "$((c+=1)): [$i]"
done
echo −−−
echo 'IFS unchanged, using $*'
c=0
for i in $*
# unquoted
do echo "$((c+=1)): [$i]"
# This line remains the same in every instance.
# Echo args.
Chapter 9. Variables Revisited 75