CODEWITHSUNDEEP
regexpcre
Nicolas
Nicolas

Reputation: 21

Conditional matching PCRE regex: how do a lookbehind with various size?

I try to match a simple pattern P1 (whitespaces or tabs, then ## then text):

[ \t]*##\S*

But sometimes, I want to match with another pattern P2 (neither whitespaces nor tabs, then ## then text):

[^ \t]*##\S*

P2 must be used when ##\S* follow \S*

P1 must be used otherwise

Examples of expected match results:

##foo
must give
##foo

      ##foo (6 whitespaces before pattern)
must give
      ##foo (because there is some whitespaces before the pattern ##foo and not any non-whitespace characters)

foo   ##bar
must give
##bar (because there is some non-whitespace charecters before the pattern ##foobar)

foo bar   ##foobar
must give
##foobar

I tried lookbehind method but it's not possible because there is no fixed size.

It would be very nice if someone could help me...

Upvotes: 2

Views: 75

Answers (1)

Stuart Golodetz
Stuart Golodetz

Reputation: 20656

You can achieve the effect of what you're after using capture groups:

^(\s*##\S*)|^\S+\s*(##\S*)

Then something like

     ## foo

will be matched by the first alternative, and the result can be obtained from the first capture group, whereas

foo  ## bar

will be matched by the second alternative, and the "## bar" can be obtained from the second capture group.

Upvotes: 1

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