When replacing with regexes, how do I append digits to the end of a match group?

Question

This is for Visual Studio code, but I'm not sure how relevant that is.

Here's my regex: cost:(\d\d)

I'm trying to multiply that number by 100. e.g., change cost:25 to cost:2500

But if I try this replacement, it thinks I'm asking for group #100, instead of group #1 and two zeros: cost:$100 changes cost:25 to cost:$100. If I put a space after the two zeros, it replaces it with this: cost:25 00. Is there a way to tell the regex engine where the group name stops?

I've tried replacing with cost:${1}00, but that doesn't work. It changes it to cost:${1}00:

@nhahtdh I am on the latest version. Are you sure you're not confusing it for Visual Studio? — Daniel Kaplan, Nov 24 '20 at 07:17
@nhahtdh that's odd. I checked for updates and it said I was on the latest. — Daniel Kaplan, Nov 24 '20 at 07:20
Interestingly, substitution `cost:$1$'00` works. Although `$'` means [Substituting the Text after the Match](https://learn.microsoft.com/en-us/dotnet/standard/base-types/substitutions-in-regular-expressions?redirectedfrom=MSDN) — Hao Wu, Nov 24 '20 at 07:30
@HaoWu: Interestingly, `$'` in replacement gives literal replacement for me. I don't understand what is happening anymore — nhahtdh, Nov 24 '20 at 07:34
@nhahtdh In my case `$100` works as expected without any issue. I'm using `1.52.0-insider` though — Hao Wu, Nov 24 '20 at 07:36

score 3 · Answer 1 · answered Nov 24 '20 at 07:10

3

Instead of using groups, why not match the zero-width character using lookbehind?

(?<=cost:\d\d)

replacement:

answered Nov 24 '20 at 07:10

Hao Wu

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That works! I hope you understand, but I don't want to accept this as the answer because it's only contextual that this solution works for me. I'd still like to know how to do what the title says. But have an upvote – Daniel Kaplan Nov 24 '20 at 07:12
nice +1, you could also use `\d+` – vrintle Nov 24 '20 at 07:13
@DanielKaplan I agree with you, this is only avoiding the problem, not actually solves it. – Hao Wu Nov 24 '20 at 07:15

nhahtdh · Accepted Answer · 2020-11-26T08:29:36.170

3

On VS Code 1.51.1, this solution works for Replace (current file) and Replace in Files:

Use $0 to refer to the whole match:

Search: cost:\d\d

Replace: $000

As mentioned in the comment, these two methods only works for Replace (current file) but not Replace in Files:

Use $& to refer to the whole match:

Search: cost:\d\d

Replace: $&00
Use $1 to refer to the first capturing group:

Search: cost:(\d\d)

Replace: cost:$100

For the regular Replace, the replacement string parsing rule is the same as JavaScript. Since we don't have 10 or 100 capturing groups in the regex, the replacement string is parsed as $1 (whatever matched in group 1) followed by literal 00

However, for Replace in Files, the replacement only works when there is only 1 digit following the $1 (cost:$10). Once there are more than 2 digits, it's treated as literal string replacement

I played around with named capturing groups - while they are recognized in the search field, I can't refer to it in replacement string. Common syntax such as ${group} and $<group> doesn't work.

After testing a bit more, I find some weird bugs with how Replace in Files is implemented.

This straight-forward method with named capturing group doesn't work:

Search: cost:(?<n>\d\d)

Replace: cost:$<n>00

But we can coax it to work by mixing named capturing group replacement with numbered group replacement:

Search: cost:(?<n>\d\d)()

Replace: cost:$2$<n>00

We can also apply this trick to get the numbered group replacement to work:

Search: cost:(\d\d)()

Replace: cost:$2$100

Seems that there is a bug when the replacement string only includes a single replacement token.

edited Nov 26 '20 at 08:29

answered Nov 24 '20 at 07:22

nhahtdh

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I wish I knew why that first one didn't work for me. I'm on the same version (1.51.1). – Daniel Kaplan Nov 24 '20 at 07:30
#2 does work for me though. I wish I knew why none of the others didn't. – Daniel Kaplan Nov 24 '20 at 07:32
What OS are you on? I'm on Windows – Daniel Kaplan Nov 24 '20 at 07:33
I just put up a screenshot of About screen @DanielKaplan – nhahtdh Nov 24 '20 at 07:36
#1 works in the Find widget but not Search across Files. #2 works in Find and Search. #3 works in the Find widget but not Search across Files. I presume @nhahtdh tested them in the Find widget but the OP is using the Search across Files panel instead. – Mark Nov 25 '20 at 00:08
@Mark That's exactly what I did – nhahtdh Nov 26 '20 at 07:51
@DanielKaplan Updated with some more testing - so damn buggy – nhahtdh Nov 26 '20 at 08:30

Mark · Answer 3 · 2020-11-24T18:25:53.703

You have run into this bug discussed here: VSCode Regex Find/Replace In Files: can't get a numbered capturing group followed by numbers to work out

and the filed issue: https://github.com/microsoft/vscode/issues/102221

which was unfortunately closed with "ask on SO response" despite having originated here. Although there are workarounds - also noted in the So link here, you can still comment on the issue and ask it to be reopened.

The weird thing is that if you add just one digit like cost:$10 it works just fine - that is why I consider this a bug.

When replacing with regexes, how do I append digits to the end of a match group?

3 Answers3