CODEWITHSUNDEEP
javascriptregex
Dog
Dog

Reputation: 2906

Regular Expression Results Not as Expected

I have the following string:

string = 1231231223123131_FILE_NAME.EXTENSION.OTHEREXTENSION

and the following regular expression:

string.match(/^\d+_([^.]+\.[^.]+)/)[1]

the regular expression returns:

 => FILE_NAME.EXTENSION

While I understand that ^\d+_ is indicating find one of more digits followed by an underscore, my confusion is in the capture group. Particularly why [^.]+ seems to be returning one or more characters before a period and then including the period, but excluding the second period with the second instance of [^.]+

This regular expression combination is even more confusing when you remove the first [^.]+, because then it returns the .OTHEREXTENSION as well.

From my understanding using the caret inside a parentheses [^.] means to exclude whatever follows it. So why in this instance is it including all characters up to and after the first period?

Upvotes: 1

Views: 45

Answers (2)

Robo Mop
Robo Mop

Reputation: 3553

In your regex, you have [^.]+\.[^.]+

[^.]+ stands for one or more, non-period characters which matches FILE_NAME, and stops when it reaches the period .

\. matches a single period ., which it does (after FILE_NAME but before EXTENSION.OTHEREXTENSION).

The next [^.]+ matches one or more, non-period characters again, which is EXTENSION, and stops again when it reaches the period .

Upvotes: 2

You Old Fool
You Old Fool

Reputation: 22941

Your capturing group says any character that's not a . then a single . then another group of non . characters. The . in your result is not coming from the first [^.]+, it's coming from the \. that follows it and is still within the capturing group.

FILE_NAME.EXTENSION meets that criteria. FILE_NAME matches the first character class 1 or more times. This is followed by a dot which matches \. Then the word EXTENSION meets the second character class one or more times. When it reaches the 2nd dot the capturing group comes to an end since the regex contains nothing further to match a second .

Upvotes: 1

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