[Shell Script](EN) Convert between upper case letter and lower case letter

Post about converting between upper case letter and lower case letter in shell script(bash)

Environment and Prerequisite

• Shell Script
• Bash

Convert

Upper case -> Lower case

• POSIX standard

test="THIS is TeSt"
echo "$test" | tr '[:upper:]' '[:lower:]'

• Bash over 4.0

test="THIS is TeSt"
echo "${test,,}"

Lower case -> Upper case

• POSIX standard

test="THIS is TeSt"
echo "$test" | tr '[:lower:]' '[:upper:]'

• Bash over 4.0

test="THIS is TeSt"
echo "${test^^}"

Reference

• https://www.cyberciti.biz/faq/linux-unix-shell-programming-converting-lowercase-uppercase/
• https://stackoverflow.com/questions/2264428/how-to-convert-a-string-to-lower-case-in-bash