Prevent regex from matching slash characters

Question

I have the following regex \/\/.*\/.*? and I am applying it to strings in this format: mongodb://localhost:27017/admin?replicaSet=rs

Based on the above the returned match is: //localhost:27017/ however, I do not want the //../ characters I only want the result to be: localhost:27017

What needs to be modified in order to achieve this, I am fairly new to regex building.

Edit: I am using Java 1.7 to execute this regex statement.

What language are you using? You might be better off using existing code that extracts the hostname and port number from URLs rather than messing with a regex to do it. — Andy Lester, Jul 13 '15 at 16:25
I don't know about Java, but there has to be a URL parsing function somewhere, I would think. I know that in PHP, use the [`parse_url`](http://php.net/manual/en/function.parse-url.php) function. Perl: [`URI` module](http://search.cpan.org/dist/URI/). Ruby: [`URI` module](http://www.ruby-doc.org/stdlib-1.9.3/libdoc/uri/rdoc/URI.html). .NET: ['Uri' class](http://msdn.microsoft.com/en-us/library/txt7706a.aspx) — Andy Lester, Jul 13 '15 at 17:08
Here you go: https://stackoverflow.com/questions/13408498/parsing-a-url-in-java — Andy Lester, Jul 13 '15 at 17:10

Wiktor Stribiżew · Accepted Answer · 2015-07-13T16:35:49.397

You can use this replaceAll approach in Java if you do not want to use Matcher:

System.out.println("mongodb://localhost:27017/admin?replicaSet=rs".replaceAll("mongodb://([^/]*).*", "$1"));

Here, I assume you have 1 occurrence of a mongodb URL. mongodb:// matches the sequence of characters literally, the ([^/]*) matches a sequence of 0 or more characters other than / and stores them in a capturing group 1 (we'll use the backreference $1 to this group to retrieve the text in the replacement pattern). .* matches all symbols up to the end of a one-line string.

See IDEONE demo

Or, with Matcher,

Pattern ptrn = Pattern.compile("(?<=//)[^/]*");
Matcher matcher = ptrn.matcher(str);
while (matcher.find()) {
   System.out.println(matcher.group());
}

The regex here - (?<=//)[^/]* - matches again a sequence of 0 or more characters other than / (with [^/]*), but makes sure there is // right before this sequence. (?<=//) is a positive lookbehind that does not consume characters, and thus does not return them in the match.

I added explanations and some links. Please let me know if there is anything unclear about this. Lots of people don't like `Matcher` since it requires adding another `import`, and more code, but it helps you retrieve matches or capturing groups individually. — Wiktor Stribiżew, Jul 13 '15 at 16:41

score 0 · Answer 2 · answered Jul 13 '15 at 16:41

You can use a combination of lookbehinds and lookaheads to replace all the "/" like: (?<=\/\/).+.*(?=\/).*?

Will match only localhost:27017 from your query

Here the (?<=\/\/). is matching to anything after the "//" string and the (?=\/) is matching anything before the "/" string

Prevent regex from matching slash characters

2 Answers2