Need a RegEx that matches only a single instance of the pipe character

Question

I'm trying to write a RegEx to only match instances of the 'pipe' character (|) that are NOT followed by one or more further pipes. So a pipe followed by anything other than a pipe.

I have this but it doesn't appear to be working:

/|(?!/|)

Update: This is matching pipes not followed by a pipe but I need it to also not match where there is a pipe BEFORE also. \|(?!\|) — codernaut
– codernaut, Commented Feb 7, 2013 at 16:24

Rohit Jain · Accepted Answer · 2013-02-07 16:20:08Z

You are escaping your pipe wrongly. You need to use backslash, and not slash. Apart from that, you also need to use negative look-behind, so that the last pipe is not matched, which is probably not preceded by a pipe, but not followed by it: -

(?<!\|)\|(?!\|)

Generally, I prefer to use character class rather than escaping if I want to match regex meta-character class: -

(?<![|])[|](?![|])

But, it's my taste.

Thanks! However this is now matching double pipes too. I only want to match a pipe not followed by a pipe.

Alan Moore · Accepted Answer · 2013-02-09 00:06:07Z

1

Okay, I found the answer, after much iteration. This will match ONLY a single pipe character not proceeded AND not followed by a pipe.

(?=(\|(?!\|)))((?<!\|)\|)

edited Feb 9, 2013 at 0:06

Alan Moore

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answered Feb 7, 2013 at 16:41

codernaut

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1 Comment

Alan Moore Over a year ago

This is the same as Rohit's answer, only less readable. You should accept that one.

P O'Conbhui · Accepted Answer · 2013-02-08 23:54:45Z

Match a (start of line or a non-pipe) a pipe (an end of line or a non-pipe).

(^|[^|])[|]([^|]|$)

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