From LQWiki

rev is the same as cat, only rev shows characters in reverse. Imagine a file foo that contains:

hello
world

rev foo will print:

olleh
dlrow

to print lines in reverse you can use tac, to print both lines and characters in reverse, for example, use:

tac foo | rev

Provided by

Most (all?) Linux distributions incorporate this from the GNU Coreutils: and use its man page

Related Commands

These all relate to the output or processing of entire files

• cat -- concatenate files into a single result.
• tac -- line-reversed cat
• nl -- output with line numbers
• od -- dump in octal and other character representations.
• base64 -- Encode in printable characters.