Using rename to rename upper case to lower case and add a character

Question

On linux, using rename to rename multiple directories. I want to rename directories starting with higher case characters to lower case and add a special character, let's say _ before the first letter.

For example I want to rename Myfile to _myfile

The best I came up with so far is :

rename -n 'y/[A-Z]/[a-z]' *

But when I add my character to this regular expression I get the following error :

rename -n 'y/[A-Z]/_[a-z]' *
Replacement list is longer than search list at (eval 90) line 1.

How can I add the special character to the regular expression?

Answer 1

Do:

rename -n 's/^([A-Z])/_\L$1/' */

• ^([A-Z]) matches any uppercase letter at start, and put in captured group 1

• In the replacement, we are lowercasing (\L) the captured group 1 with perpending a _

• */ matches only directories

Remove -n for actual renaming action:

rename 's/^([A-Z])/_\L$1/' */