Shell script tricks

1. The array of shell script 

names=( Jennifer Tonya Anna Sadie )
for name in ${names[@]}
do
   echo $name
done

names=( Jennifer Tonya Anna Sadie )
for (( i = 0 ; i < ${#names[@]} ; i++ ))
do
    echo ${names[$i]}
done

2. Variable substitution for shell script 

$DEVICE0=eth0
$echo "Configure interface " ${!DEVICE${i}}

$n=1
$ eval echo \${$n}

$ n="date"
$ echo $($n)

Output :Wed May 21 20:39:00 EEST 2008
3. Increment i in the while loop 

i=$(($i+1))
i=`expr i + $i`