HowTo: Reverse a String In Unix / Linux Shell?

Posted on in Categories , , last updated July 6, 2012

How do I reverse lines of a file or files under Linux or Unix like operating systems?

You can use any one of the following method.

Say hello to rev command

The rev command copies the specified files, reversing the order of characters in every line. If no files are specified, the standard input (from keyboard) is read. If rev command is installed use it as follows:

echo "nixcraft" | rev

Sample outputs:

tfarcxin

You can use the following syntax too:

rev<<<"This is a test"

Sample outputs:

tset a si sihT

Perl script example to reverse a string

You can use the perl and syntax is:

perl -ne 'chomp;print scalar reverse . "\n";'<<<"nixcraft"

OR

echo 'nixcraft' | perl -ne 'chomp;print scalar reverse . "\n";'

Bash shell script example to reverse a string

You can use bash and sample bash script is:

#!/bin/bash
input="$1"
reverse=""
 
len=${#input}
for (( i=$len-1; i>=0; i-- ))
do 
	reverse="$reverse${input:$i:1}"
done
 
echo "$reverse"

Run it as follows:
./script nixcraft
Sample outputs:

tfarcxin

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

6 comment

  1. Python equivalent:

    echo foo | python -c 'import sys;print(sys.stdin.read().strip()[::-1])'
    python -c 'import sys;print(sys.stdin.read().strip()[::-1])' &lt;&lt;&lt; foo

    PHP equivalent:

    echo foo | php -r &#039;print strrev(trim(fgets(STDIN)));&#039;
    php -r &#039;print strrev(trim(fgets(STDIN)));&#039; &lt;&lt;&lt; foo
  2. I am looking to reverse 4 digits in a string, could you please let me know what would be syntax, and data will be 178126*********4321 , it is not a column, so it possible if we can identify the position of charcter like 12 th to 16 charecter needs to be reveresed , is it possible, if yes could you please let me know the syntax.

    Thanks
    Radha

    1. Can be done using awk split function. Example reversing the three middle characters of a string:

      echo 1234567 | awk '{split($1,a,"");printf("%s%s%s%s%s%s%s",a[1],a[2],a[5],a[4],a[3],a[6],a[7])}'

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