regex, extract string NOT between two brackets

21
votes

OK regex question , how to extract a character NOT between two characters, in this case brackets.

I have a string such as: word1 | {word2 | word3 } | word 4

I only want to get the first and last 'pipe', not the second which is between brackets. I have tried a myriad of attempts with negative carats and negative groupings and can't seem to get it to work.

Basically I am using this regex in a JavaScript split function to split this into an array containing: "word1", "{word2 | word3}", "word4".

Any assistance would be greatly appreciated!

2
regex
What 'bar'? That's not in your example. - Carl Norum
What language or tool are you using ? Can you show us some of what you have tried ? - Ibrahim Najjar
@CarlNorum He means word1 which is before the vertical bar | :) - Ibrahim Najjar
sorry about that. I changed the word 'bar' to 'pipe' in the question above. thx. - shaun stewart

2 Answers

32
votes

On refiddle.com set to JavaScript, try using this pattern

/\|(?![^{]*})/g

with this text

word1 | {word2 | word3 } | word 4 | word 4 | {word2 | word3 }

This should match all of the Pipe symbols that are not inside {}.

20
votes

Depends on the language/implementation you're using, but...

\|(?![^{]*})

This matches a pipe that is not followed by a } except in the case that a { comes first.

The (?! ... ) is known as a negative lookahead assertion. This is easier to understand if we start with a positive lookahead assertion:

\|(?=[^{]*})

The above only matches a pipe that is followed by a } without encountering a { first. When you negate that by replacing the = with a !, the match is now only successful if there's no way for the positive case to be true (also known as the complement).