perl regular expression

Question

I am having some URLs in this format. Some URLs contain &abc=4 and some not.

xxxxxxxxxxxxxxxxxxxxxxxxxxx&abc=4
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx&abc=4
xxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx

here xxxxxxxxxxxxxxxxxxxxx is string

I want to match URLs which have xxxxxxxxxxxxxxxxx only and not &abc=4(meaning I want to get these type of URLs, only xxxxxxxxxxxxxx, xxxxxxxxxxxxxx, xxx)

I know how to write a regular expression which matches the entire url. For example: /x.*abc=4/

But how do I write a regular expression that matches only xxxxxxxxxx and not &abc=4?

first check for a match with xxxx, then check for the absence of abc=4 — knittl
– knittl, Commented Mar 3, 2011 at 11:46

stema · Accepted Answer · 2011-03-03 13:50:26Z

1

I would use negative look-ahead assertion (Look ahead what is not allowed to follow my pattern)

^(?!.*&abc=4$).*$

This pattern will match any string that does not end with &abc=4

you can verify it online here: http://www.rubular.com/

answered Mar 3, 2011 at 13:50

stema

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Comments

Benoit · Accepted Answer · 2011-03-03 11:57:54Z

0

Use negative lookbehind assertion. The form is:

(?<![&?]abc=4)

(this will also exclude ?abc=4).

edited Mar 3, 2011 at 11:57

answered Mar 3, 2011 at 11:46

Benoit

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Comments

Nathan Fellman · Accepted Answer · 2011-03-03 13:01:10Z

0

Assuming your URLs are on each line, you can use:

([^&]+?)

This basically will match anything up to the the first instance of &.

As @Benoit said, you can do this using a zero width expression to negate the capture of the query string, but you would be after a positive lookahead, and not a negative lookbehind, syntax example below:

(?=(&[^=]+?\d+)+)

As you can see though, this would complicate the expression a touch.

Hope this helps.

edited Mar 3, 2011 at 13:01

Nathan Fellman

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answered Mar 3, 2011 at 12:03

Pooli

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1 Comment

Pooli Over a year ago

That's a negative lookahead, so what your asking for is everything up to the point that it would not be followed by the &=444 point. A positive lookahead allows you to say everything up the point that it is followed by this.

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