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I have a string like the following "blaa...blup..blaaa...bla."

Every part where there is more than one dot must be replaced by "_" but it must have the same amount as replaced chars.

The string should result in: "bla___blup__blaaa___bla."

Notice that the last dot is not replaced as it has not other dots "connected".

I tried using following regex approach in powershell but I always get a legnth of 2 for the match regardless if there where 3 or more dots:

$string -replace '(.)\1+',("_"*'$&'.length)

Any ideas?

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  • 1
    Possible duplicate of Use a function in Powershell replace Commented Feb 8, 2016 at 14:35
  • @PetSerAl: Why? It can be easily solved with a single regex. Commented Feb 8, 2016 at 14:36
  • @WiktorStribiżew Given the OP code, I think it what he trying to do, so I vote for it. Commented Feb 8, 2016 at 14:58
  • Yeah, true. I will add a note about that in my answer. Commented Feb 8, 2016 at 14:59
  • Thanks for all the answers, I could solve my problem with this. Commented Feb 8, 2016 at 16:38

3 Answers 3

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7

You can use the \G anchor to glue a match to the previous.

\.(?=\.)|\G(?!^)\.
  • \.(?=\.) match a period if another one is ahead.
  • |\G(?!^)\. or replace period if there was a previous match (but not start)

Replace with underscore. See demo at regexstorm

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:) Good choice of the alternatives :) Yours seems the best suggestion.
4

You can use the following pattern:

\.(?=\.)|(?<=\.)\.

And replace with _.

The pattern simply looks for either a period that is preceded by a period or a period which is followed by a period:

  • \.(?=\.) - Matches a period which is followed by a period
  • | - Or
  • (?<=\.)\. - Matches a period which is preceded by a period

See the online demo.

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3

None of the languages and regex flavors I know allow you to evaluate the backreference numeric value "on the fly", you can only use it in the callback function. See Use a function in Powershell replace.

However, in this particular case, you can use the following regex:

((?=\.{2})|(?!^)\G)\.

And replace with _.

See the regex demo here.

enter image description here

And the explanation:

  • ((?=\.{2})|(?!^)\G) - a boundary that either matches a location before 2 dots (with (?=\.{2})) or the end of the previous successful match (with (?!^)\G)
  • \. - a literal dot.
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@Shihan: bobble bubble's suggestion is the most efficient although all regexps here are working as you expect.

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