rename the last number-string

Question

How to rename the last number-string it finds with a zero-padded version and leave the rest of the filename alone?

AAA 2000-01-03 bbb 2001-03-04 page_1.pdf

To:

AAA 2000-01-03 bbb 2001-03-04 page_0001.pdf

See:

• Renaming hundreds of files at once for proper sorting
• How to zero pad numbers in file names in Bash? (on Stack Overflow)

Answer 1

The simplest thing would probably be to match the preceding page_ string

Ex:

$ rename -n 's/page_(\d+)/sprintf "page_%04d", $1/e' *.pdf
rename(AAA 2000-01-03 bbb 2001-03-04 page_1.pdf, AAA 2000-01-03 bbb 2001-03-04 page_0001.pdf)

(remove the -n when you are happy that it is doing the right thing).

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If you really need to match the "last number", you could use positive lookahead to anchor the match to the end of the string $ with a possibly empty sequence of non-digits between:

$ rename -n 's/(\d+)(?=\D*$)/sprintf "%04d", $1/e' *.pdf
rename(AAA 2000-01-03 bbb 2001-03-04 page_1.pdf, AAA 2000-01-03 bbb 2001-03-04 page_0001.pdf)