Changing all file's extensions in a folder using CLI in Linux

Question

How to change all file's extensions in a folder using one command on CLI in Linux?

Answer 1

You could use a for-loop on the command line:

for foo in *.old; do mv $foo `basename $foo .old`.new; done

this will take all files with extension .old and rename them to .new

Answer 2

Use rename:

rename 's/.old$/.new/' *.old