Regex to substitute character with numbers around it in filenames with rename utility (perl based)

Question

I would like to rename files that have the following format:
somethingblabla15T06:58_31+0000somethingblabla.bla
THe new name should be
somethingblabla15T06:58:31+0000somethingblabla.bla
So the _ within the numbers should be replaced with :.
I would like to do this with the perl based rename command line tool.
I thought this would be a part of the regex:
's/[0-9](_)[0-9]/:'
I can't get it to work. I think this should also be escaped or so.

John1024 · Accepted Answer

Try:
rename 's/([0-9])_([0-9])/$1:$2/'

Example
Consider a directory with this file:
$ ls som*
somethingblabla15T06:58_31+0000somethingblabla.bla

Let's run rename and then run ls again:
$ rename 's/([0-9])_([0-9])/$1:$2/' s*
$ ls som*
somethingblabla15T06:58:31+0000somethingblabla.bla

How it works
([0-9])_([0-9]) matches a digit followed by an underscore followed by a digit.  Because of the parens, each digit is saved in a group.  The replacement text is $1:$2 where $1 refers to the first saved group and $2 to the second saved group.

Toto · Answer

Another way to do the job without capture groups:
rename 's/(?<=d)_(?=d)/:/' something*

Explanation:
s/              # substitute
    (?<=d)       # positive lookbehind, make sure we have a digit before
    _             # underscore
    (?=d)        # positive lookahead, make sure we have a digit after
/               # with
    :             # colon
/               # end subst.

Regex to substitute character with numbers around it in filenames with rename utility (perl based)

2 Answers

Example

How it works

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