≡ Menu

Bash C Style For Loop Example and Syntax

How do I use the bash C style for loop under UNIX or Linux operating systems?

The bash C-style for loop share a common heritage with the C programming language. It is characterized by a three-parameter loop control expression; consisting of an initializer (EXP1), a loop-test or condition (EXP2), and a counting expression (EXP3). The syntax is as follows:

for (( EXP1; EXP2; EXP3 ))

Bash C-Style Example

# Display message 5 times
for ((i = 0 ; i < 5 ; i++)); do
  echo "Welcome $i times."

Sample outputs:

Welcome 0 times.
Welcome 1 times.
Welcome 2 times.
Welcome 3 times.
Welcome 4 times.

Read An Array Using C Style For Loop

Bash provides one-dimensional array variables. An array is created automatically using the following compound assignments syntax:

array=( item1 item2 item3 ... itemN)

You can read an array using for loop as follows:

# define an array called fruits
fruits=("Apple" "Mango" "Pineapple" "Banana" "Orange" "Papaya" "Watermelon")
len=${#fruits[*]}         # get total elements in an array
# print it
for (( i=0; i<${len}; i++ ));
	echo "${fruits[$i]}"

Here is another practical example that generates lighttpd web server configuration file to log real IP address of the visitors:

_frontend_proxy_lan_ips=("" "" "" "" "")
at=${#_frontend_proxy_lan_ips[*]}         # get total elements in an array
echo '### Log real client ips on all backends ###' >"$t"
echo 'server.modules += ( "mod_extforward" )'   >>"$t"
echo 'extforward.headers = ("X-Forwarded-For")' >>"$t"
echo 'extforward.forwarder = (' >>"$t"
# For loop 
for (( i=0; i<${at}; i++ ));
	[ $i -lt $(( $at - 1 )) ] && s="," || s=""      # remove , for last item in an array
        echo "      \"${_frontend_proxy_lan_ips[$i]}\" => \"trust\"${s} " >>"$t"
echo ')' >>"$t"
# Copy it
cp -f "$t" /etc/lighttpd/
# remove temp file
[ -f "$t" ] && rm -f "$t"

Sample outputs (sample config file generated by above script):

### Log real client ips on all backends ###
server.modules += ( "mod_extforward" )
extforward.headers = ("X-Forwarded-For")
extforward.forwarder = (
      "" => "trust", 
      "" => "trust", 
      "" => "trust", 
      "" => "trust", 
      "" => "trust" 
Share this tutorial on:

Your support makes a big difference:
I have a small favor to ask. More people are reading the nixCraft. Many of you block advertising which is your right, and advertising revenues are not sufficient to cover my operating costs. So you can see why I need to ask for your help. The nixCraft, takes a lot of my time and hard work to produce. If you use nixCraft, who likes it, helps me with donations:
Become a Supporter →    Make a contribution via Paypal/Bitcoin →   

Don't Miss Any Linux and Unix Tips

Get nixCraft in your inbox. It's free:

{ 2 comments… add one }
  • kmkkmk June 10, 2011, 3:26 pm


    I have just stumbled upon this site and like it a lot. Yet when reading Bash I was immediately thinking about Zsh and that I should have switched from to Zsh rather earlier than later. I would hardly put any effort in Bash and spent the time on Zsh instead.

    Keep up the good work.

  • Jotne October 10, 2012, 5:54 am

    More simple example of array

    GNU nano 2.2.6 File: a Modified

    fruits=("Apple" "Mango" "Pineapple" "Banana" "Orange" "Papaya" "Watermelon")
    for I in ${fruits[*]}; do
            echo $I
Security: Are you a robot or human?

Leave a Comment

You can use these HTML tags and attributes: <strong> <em> <pre> <code> <a href="" title="">

   Tagged with: , , , , , , , , , , , , , ,