CODEWITHSUNDEEP
regexeclipseregex-lookarounds
jmrah
jmrah

Reputation: 6241

Match a pattern preceded by a specific pattern without using a lookbehind

Is there a way to match a B only if preceded by an A? The A can be at any position behind the B, with any amount of characters between. Examples:

A_B (Matches `B`)

C_B (No match)

I've tried:

(?=A)[^B]*B

But it matches all the characters preceeding B as well. My regex engine does not support variable length look-behinds. Is there any way I can do this?

Edit: I am currently using the built in regex search in Eclipse, however, I am using regex101.com to test things out.

Upvotes: 1

Views: 49

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726899

A work-around for the lack of variable-length lookbehind is available in situations when your strings have a relatively small fixed upper limit on their length. For example, if you know that strings are at most 100 characters long, you could use {0,100} in place of * or {1,100} in place of + inside the lookbehind expression:

(?<=A[^B]{0,100})B

When the length of your string has no obvious upper limit, you could drop lookbehind altogether, use a non-capturing group in its place, place a capturing group over B, and use the content of that group as the result of your regular expression.

Upvotes: 2

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