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I have a URL, and I'm trying to match it to a regular expression to pull out some groups. The problem I'm having is that the URL can either end or continue with a "/" and more URL text. I'd like to match URLs like this:

But not match something like this:

So, I thought my best bet was something like this: 

/(.+)/(\d{4}-\d{2}-\d{2})-(\d+)[/$]

where the character class at the end contained either the "/" or the end-of-line. The character class doesn't seem to be happy with the "$" in there though. How can I best discriminate between these URLs while still pulling back the correct groups?

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4 Answers 4

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140

To match either / or end of content, use (/|\z)

This only applies if you are not using multi-line matching (i.e. you're matching a single URL, not a newline-delimited list of URLs).


To put that with an updated version of what you had:

/(\S+?)/(\d{4}-\d{2}-\d{2})-(\d+)(/|\z)

Note that I've changed the start to be a non-greedy match for non-whitespace ( \S+? ) rather than matching anything and everything ( .* )

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2 Comments

How do I give you more point ;) Thanks for this. Just to document (/|\A) would match forward slash or beginning of string.
Note: JavaScript doesn't support \Z and \z
70

You've got a couple regexes now which will do what you want, so that's adequately covered.

What hasn't been mentioned is why your attempt won't work: Inside a character class, $ (as well as ^, ., and /) has no special meaning, so [/$] matches either a literal / or a literal $ rather than terminating the regex (/) or matching end-of-line ($).

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This is something frequently forgotten and not mentioned eneough in the regex docs.
Note that ^ can have special meaning in a character class. If it is the first character in the class, it makes it a negative class that will match anything except the other characters. e.g. to match anything except a or b, you could use [^ab]. To include a literal ^, just make sure it isn't first, so to match either a, b or ^ you would use [ab^].
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/(.+)/(\d{4}-\d{2}-\d{2})-(\d+)(/.*)?$

1st Capturing Group (.+)

.+ matches any character (except for line terminators)

  • + Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)

2nd Capturing Group (\d{4}-\d{2}-\d{2})

\d{4} matches a digit (equal to [0-9])

  • {4} Quantifier — Matches exactly 4 times

- matches the character - literally (case sensitive)

\d{2} matches a digit (equal to [0-9])

  • {2} Quantifier — Matches exactly 2 times

- matches the character - literally (case sensitive)

\d{2} matches a digit (equal to [0-9])

  • {2} Quantifier — Matches exactly 2 times

- matches the character - literally (case sensitive)

3rd Capturing Group (\d+)

\d+ matches a digit (equal to [0-9])

  • + Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)

4th Capturing Group (.*)?

? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)

.* matches any character (except for line terminators)

  • * Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)

$ asserts position at the end of the string

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Why doesn't the last / need to be escaped?
the 4th capturing group is (/.*)? not (.*)? the whole point of the question was revolving around the possible ending slash too. If that's a typo is ok
23

In Ruby and Bash, you can use $ inside parentheses.

/(\S+?)/(\d{4}-\d{2}-\d{2})-(\d+)(/|$)

(This solution is similar to Pete Boughton's, but preserves the usage of $, which means end of line, rather than using \z, which means end of string.)

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PHP too from what I can tell. I see no reason why $ can't be used in parenthesis () in any implementation actually. It's the brackets [] that make it literal.
$ works this way in javascript, whereas \z doesn't (Chrome 48, Firefox 43, IE9).
This is the most straight-forward option. Match slash or end-of-line. It even matches the title of this question!

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