[bash] How do I rename the extension for a bunch of files?

Rename file extensions for all files under current directory and sub directories without any other packages (only use shell script):

  1. Create a shell script rename.sh under current directory with the following code:

    #!/bin/bash
    
    for file in $(find . -name "*$1"); do
      mv "$file" "${file%$1}$2"
    done
    
  2. Run it by ./rename.sh .old .new.

    Eg. ./rename.sh .html .txt