Modify regex to filter input containing certain strings

Question

I have this regex: /href=('|")(\w+|\/dashboard)/ that matches every HTML anchor that has an href that starts with /dashboard, or something/without/a/slash/at/the/beginning.

So this regex matches:

<a href="/dashboard/security-settings"></a>
<a href='dashboard/security-settings'></a>
<a href='something/security-settings'></a>

But not:

<a href="/home"></a>
<a href="/about"></a>

The issue here is that it also matches:

<a href="http://www.google.com"></a>
<a href="www.facebook.com"></a>

How can I filter href's starting with http or www from the regex? I tried playing with the ^ operator with no luck:

href=('|")(([^http][^www]|\w+)|\/dashboard)

which language?...why use regex?use an html parser

Anirudha
– Anirudha

2013-07-04 13:22:31 +00:00
Commented Jul 4, 2013 at 13:22 — Anirudha
– Anirudha, Commented Jul 4, 2013 at 13:22

Tim Pietzcker · Accepted Answer · 2013-07-04 13:22:38Z

1

^ within a character class works on individual letters, not strings. So [^http] actually means "Match one character that's neither an h nor a t nor a p".

You need a negative lookahead assertion instead:

href=(['"])(?!http|www)(\w+|/dashboard)

answered Jul 4, 2013 at 13:22

Tim Pietzcker

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Felix Glas · Accepted Answer · 2013-07-04 14:52:04Z

0

The simplest solution is:

/^href=['"](\w+|\/dashboard)/

The ^ operator (if used at the start of the regexp) makes sure that the regexp is only matched at the beginning of the line, so it only matches strings that begin with href.

As others have mentioned you can use negative lookahead to explicitly filter out strings that begin with http or www. However, if the string would start with ftp:// (or any prefix other than "http" or "www") it would still be matched using negative lookahead for "http" and "www". It seems better to use a white list in this case rather than a black list containing everything that you don't want to match.

edited Jul 4, 2013 at 14:52

answered Jul 4, 2013 at 14:06

Felix Glas

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