$ Linux Command

Text

rev

Reverse characters in each line of a file.

textreversecolumnscharactersstring

Additional Notes

rev reverses the order of characters on each line of input. The last character becomes the first, the second-to-last becomes the second, and so on. It operates line-by-line and outputs each reversed line.

rev is a simple utility in the util-linux package. It is useful for specialized text processing tasks like reversing columns, creating palindromes, or solving certain data extraction problems where reversing lines simplifies the work.

Syntax

rev [options] [file...]

Parameters

  • file: One or more files to process. If no file is given, rev reads from standard input.

Common Options

  • -V, --version: Show version information.
  • -h, --help: Show help and exit.

Examples

echo "hello" | rev

Reverse the word hello to olleh.

rev file.txt

Reverse every line in file.txt.

cat data.txt | rev

Reverse lines from standard input.

echo "123 456 789" | rev

Reverses to 987 654 321.

cut -d: -f1 /etc/passwd | rev

Reverse each username in the password file.

echo "racecar" | rev

Palindrome test: If the output matches the input, the word is a palindrome.

rev file.txt | sort | rev

Sort lines by their reversed content (equivalent to sorting from right to left).

paste <(cut -f1 data.txt) <(cut -f2 data.txt | rev)

Reverse only the second column in a tab-separated file.

Practical Notes

  • rev is line-oriented. It does not reverse the order of lines, only the characters within each line.
  • Use tac (reverse of cat) to reverse the order of lines themselves.
  • For reversing fields (words), use awk '{ for(i=NF; i>0; i--) printf "%s ", $i; printf "\n" }'.
  • rev preserves trailing newlines; blank lines remain blank.
  • The command is simple but useful in one-liners and pipes where character-level reversal is needed.
  • On some systems, rev is provided by the bsdmainutils or util-linux package.