Shell Scripting: Convert Uppercase to Lowercase

Q. How do I convert uppercase words to lowercase or vise versa under BASH shell? I’ve a small shell script and I’d like to convert all incoming user input to lowercase using a shell script. A. Use tr command to convert all incoming text / words / variable data from upper to lower case or vise versa (translate all uppercase characters to lowercase).

Convert all text file data from upper to lowercase:

Type the following command at shell: $ tr '[:upper:]' '[:lower:]' <> output.txt

Convert variable data from upper to lowercase:

$ echo $VAR_NAME | tr '[:upper:]' '[:lower:]' $ echo $VAR_NAME | tr '[:lower:]' '[:upper:]'