How do I zero-pad issue numbers without changing the # prefix?

Explanation

For log files, changelogs, or issue references, you sometimes need fixed-width numeric IDs without touching surrounding syntax. This substitution uses a pattern boundary plus an expression replacement, so only the number is rewritten while the # marker stays intact.

How it works

:%s/#\zs\d\+/\=printf('%04d', submatch(0))/g

• :%s/.../.../g runs substitution on the whole buffer
• #\zs\d\+ matches digits that come after #; \zs moves the effective start of the match to just the digits
• \=printf('%04d', submatch(0)) evaluates Vimscript for each match and left-pads the number to width 4
• g updates every ticket-like match on each line

Because \zs narrows the replacement target, the prefix character is never captured or rewritten. That makes this safer than broader capture-group substitutions when formats vary.

Example

Before:

Fixes #7 and #42; supersedes #1002.

After:

Fixes #0007 and #0042; supersedes #1002.

Tips

• Change %04d to %06d (or any width) for your convention
• Use a more specific prefix (for example TICKET-) if your file contains other # uses
• Drop % and use a visual or line range when you only want part of the file