CODEWITHSUNDEEP
regexexpress
darkace
darkace

Reputation: 878

How is this Regex interpreted?

I'm a little confused about the example on this page: http://expressjs.com/en/guide/routing.html

This route path will match abcd, abxcd, abRANDOMcd, ab123cd, and so on.


app.get('/ab*cd', function(req, res) {
  res.send('ab*cd');
});

After typing this example into here: http://regexr.com/

I can't recreate the same behaviour and match abxyzcd.

Why is this and what is the difference in the regex and the way it is interpreted?

Upvotes: 0

Views: 57

Answers (3)

Enteleform
Enteleform

Reputation: 3843

It appears that the ExpressJS syntax is different than standard RegEx syntax.

This is the RegEx version of that pattern:

Lazy

If you don't use the lazy modifier ( "?" ), you will get this result:

Non-Lazy

I recommend looking into the ExpressJS syntax further to find out how they differentiate lazy & non-lazy searching.

Upvotes: 2

Stian
Stian

Reputation: 695

what you got there, isn't Regex, but a string containing a wildcard. My regex isn't very good, but I believe the * is interpreted the same way as .* in regex.

As it says in the link you supplied:

Here are some examples of route paths based on strings.

While further down you see:

Examples of route paths based on regular expressions:

So there is basically two ways to create patterns in your routes :)

Upvotes: 1

dustinroepsch
dustinroepsch

Reputation: 1170

In normal regular expresions * means that the preceding character can be matched 0 or more times, so with the regex you gave, you could match abbcd and abbbbcd etc.

If you want to match abrandomcd you could use the regex ab.*cd The . means match any character, and the star means match any number of them.

As far as I can tell the example on that expressjs page is using a different form of regular expression than regexr or another normal engine would.

This is highlighted in the text

The characters ?, +, *, and () are subsets of their regular expression counterparts. The hyphen (-) and the dot (.) are interpreted literally by string-based paths.

Found on the page.

Upvotes: 1

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