Bash tip: How to change file extensions in batch mode

Here is an example of how you can rename all .txt files in a directory to .xlf:

for file in *.txt; do mv "$file" "${file%.txt}.xlf"; done

What exactly happens here?

• for file in *.txt: This part of the command searches the current directory for all files ending with .txt. You can of course replace .txt with any extension.
• mv "$file" "${file%.txt}.xlf": The mv command takes over the renaming. ${file%.txt} removes the old ending and .xlf is added. Again, .txt and .xlf are just placeholders for the endings you want to change.

If you want to see which files are affected first, you can also test the whole thing without renaming the files straight away. Simply use this command:

for file in *.txt; do echo mv "$file" "${file%.txt}.xlf"; done

This lists all changes without actually making them. This way you can make sure that everything fits before you execute the command correctly.

This simple shell trick saves you a lot of time and makes editing lots of files at once really efficient.