The Linux rev command is useful little utility that reverses lines of text character-wise. It will take the specified file and print it to standard output, reversing the order of the characters on each line.

Here is an example:

$ cat /etc/redhat-release 
 Fedora release 29 (Twenty Nine)

$ rev /etc/redhat-release 
 )eniN ytnewT( 92 esaeler arodeF

If no file is specified, it will read standard input until you exit using CTRL+D or otherwise kill the process.

Animated gif showing how the Linux rev command works using standard input

At first it may seem silly, but like all things Linux it is only limited by your imagination. In the following quick tip, we will show you some practical uses for the rev command.

Remove Last Character from String

Using rev and the cut command you can strip the last character from a string. 

$ echo 'Remove this question mark?' | rev | cut -c 2- | rev
 Remove this question mark

Here we are using rev to reverse the line, then cutting the first character, then reversing it again. The end result is the last character ( ? ) is removed.

Strip Everything Except Last Word in a Line

Similar to the example above, we can strip everything from a line except the last word as defined by spaces.

$ echo 'Remove this question mark?' | rev | cut -d' ' -f1| rev
 mark?

By using the cut command delimited on spaces, we are able to remove everything except the first word (-f1). Using rev allows us to reverse this and remove the last word.

Sorting File Lines by Last Character

The rev command is often used to reverse lines, apply a sort and then reverse the line back to it's original state. Take the following text file as an example.

$ cat websites.txt 
 putorius.net
 ipaddr.pub
 www.putori.us
 wikipedia.org
 putorius.net
 www.wikipedia.org
 www.ipaddr.pub
 putori.us

If we wanted to sort by the last character in each line, we can use rev to revere the lines, sort by the last character, then reverse the strings back to their original state.

$ cat websites.txt  | rev | sort | rev
 ipaddr.pub
 www.ipaddr.pub
 wikipedia.org
 www.wikipedia.org
 putori.us
 www.putori.us
 putorius.net
 putorius.net

The list is now sorted alphabetically using the last letter in each line.

Conclusion

That's rev in a nutshell. The rev command has no options, it serves one purpose. Although it will probably never get used every day, you may find yourself needing it one day, I know I have.

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