Loops in Bash


The command below loops through directories listed in $PATH.

$ path=$PATH:
$ while [ $path ]; do echo " ${path%%:*} "; path=${path#*:}; done

The command below will also loop through directories in your path.

$IFS=:
$ for dir in $PATH
> do
> ls -ld $dir
> done
drwxr-xr-x    2 root     root         4096 Jun 10 20:16 /usr/local/bin
drwxr-xr-x    2 root     root         4096 Jun 13 23:12 /bin
drwxr-xr-x    3 root     root        40960 Jun 12 08:00 /usr/bin
drwxr-xr-x    2 root     root         4096 Feb 14 03:12 /usr/X11R6/bin
drwxrwxr-x    2 chirico  chirico      4096 Jun  6 13:06 /home/chirico/bin

Other ways of doing loops:

for (( i=1; i <= 20; i++))
do
echo -n "$i "
done

Note, to do it all on one line, do the following:

$ for (( i=1; i <= 20; i++)); do echo -n "$i"; done

Below, is an example of declaring i an integer so that you do not
have to preface with let.

$ declare -i i
$ i=5;
$ while (( $i > 1 )); do
> i=i-1
> echo $i
> done
4
3
2

You can also use "while [ $i -gt 1 ]; do"  in place of "while (( $i > 1 )); do"

To get a listing of all declared values

$ declare -i


Try putting a few words in the file "test"

$ while read filename; do echo  "- $filename "; done < test |nl -w1

Or, using an array

declare -a Array
Array[0]="zero"
Array[1]="one"
Array[2]="two"
for i in `seq ${#Array[@]}`
do
echo $Array[$i-1]
done