Question

76

Javascript regex for matching/extracting file extension

rated 0 times [ 78] [ 2] / answers: 1 / hits: 127677 / 13 Years ago, tue, july 5, 2011, 12:00:00

The following regex

var patt1=/[0-9a-z]+$/i;

extracts the file extension of strings such as

filename-jpg

filename#gif

filename.png

How to modify this regular expression to only return an extension when string really is a filename with one dot as separator ? (Obviously filename#gif is not a regular filename)

UPDATE Based on tvanofsson's comments I would like to clarify that when the JS function receives the string, the string will already contain a filename without spaces without the dots and other special characters (it will actually be handled a slug). The problem was not in parsing filenames but in incorrectly parsing slugs - the function was returning an extension of jpg when it was given filename-jpg when it should really return null or empty string and it is this behaviour that needed to be corrected.

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donovantyriqn

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3 Years ago

answered 13 Years ago alli · Accepted Answer

Just add a . to the regex

var patt1=/.[0-9a-z]+$/i;

Because the dot is a special character in regex you need to escape it to match it literally: ..

Your pattern will now match any string that ends with a dot followed by at least one character from [0-9a-z].

Example:

[

  foobar.a,

  foobar.txt,

  foobar.foobar1234

].forEach( t => 

  console.log(

    t.match(/.[0-9a-z]+$/i)[0]

  ) 

)

if you want to limit the extension to a certain amount of characters also, than you need to replace the +

var patt1=/.[0-9a-z]{1,5}$/i;

would allow at least 1 and at most 5 characters after the dot.