regex reverse lazy quantifier

Question

say I have this string

X,,,X,,,X,,c,,X,,,X

and I want to catch the smallest string that matches X.*c.*X, which is X,,,X,,,X,,c,,X,,,X

the regex X.*c.*X will catch X,,,X,,,X,,c,,X,,,X

by making the second quantifier lazy X.*c.*?X I get X,,,X,,,X,,c,,X,,,X

but making the first quantifier lazy makes no difference X.*?c.*?X --> X,,,X,,,X,,c,,X,,,X

How can I tell the first quantifier to also be lazy, but from the other direction?

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

explicitly disallow repetition of the starting substring.

In the example:

X[^X]*c.*?X --> XaaaXaaaXaacXaaaX

The multicharachter version:

(using negative look-around)

look for minimal XY.*c.*XY in string: XY,,,XY,,,XY,,c,,XY,,,XY

XY((?!XY).)*c.*?XY --> XY,,,XY,,,XY,,c,,XY,,,XY

edited Jun 20, 2020 at 9:12

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answered Apr 24, 2017 at 8:47

Dotan

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3 Comments

Amadan Over a year ago

This is correct. There is no "other direction" - regex always returns the earliest (leftmost) successful match. Thus, if both XaaaXaaaXaacXaaaX and XaaaXaaaXaacXaaaX match, you will always get the first one. The only way to return the second is to make sure the first one is unsuccessful.

Wiktor Stribiżew Over a year ago

A negated character class won't work for multicharacter values.

Wiktor Stribiżew Over a year ago

Yes, there is such a question on SO already. Yours is a dupe.

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regex reverse lazy quantifier

1 Answer 1

explicitly disallow repetition of the starting substring.

The multicharachter version:

3 Comments

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Collectives™ on Stack Overflow

1 Answer 1

explicitly disallow repetition of the starting substring.

The multicharachter version:

3 Comments

Your Answer

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