Regex to batch rename files in OS X Terminal

An efficient way to perform the rename operation is to construct the rename commands in a sed pipeline and feed them into the shell.

ls |
sed -n 's/\(.*\)\(123\)\(.*\)/mv "\1\2\3" "\1onetwothree\2"/p' |
sh

You can install perl based rename utility:

brew install rename

and than just use it like:

rename 's/123/onetwothree/g' *

if you'd like to test your regex without renaming any files just add -n switch