Javascript regex for matching/extracting file extension
The following regex
var patt1=/[0-9a-z]+$/i;
extracts the file extension of strings such as
filename-jpg
filename#gif
filename.png
How to modify this regular expression to only return an extension when string really is a filename with one dot as separator ? (Obviously filename#gif is not a regular filename)
UPDATE Based on tvanofsson's comments I would like to clarify that when the JS function receives the string, the string will already contain a filename without spaces without the dots and other special characters (it will actually be handled a slug ). The problem was not in parsing filenames but in incorrectly parsing slugs - the function was returning an extension of "jpg" when it was given "filename-jpg" when it should really return null or empty string and it is this behaviour that needed to be corrected.
Just add a . to the regex
var patt1=/.[0-9a-z]+$/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] .
eg
foobar.a
foobar.txt
foobar.foobar1234
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}$/i;
would allow at least 1 and at most 5 characters after the dot.
Try
var patt1 = /.([0-9a-z]+)(?:[?#]|$)/i;
This RegExp is useful for extracting file extensions from URLs - even ones that have ?foo=1 query strings and #hash endings.
It will also provide you with the extension as $1 .
var m1 = ("filename-jpg").match(patt1);
alert(m1); // null
var m2 = ("filename#gif").match(patt1);
alert(m2); // null
var m3 = ("filename.png").match(patt1);
alert(m3); // [".png", "png"]
var m4 = ("filename.txt?foo=1").match(patt1);
alert(m4); // [".txt?", "txt"]
var m5 = ("filename.html#hash").match(patt1);
alert(m5); // [".html#", "html"]
PS +1 for @stema who offers pretty good advice on some of the RegExp syntax basics involved.
Example list:
var fileExtensionPattern = /.([0-9a-z]+)(?=[?#])|(.)(?:[w]+)$/gmi
//regex flags -- Global, Multiline, Insensitive
var ma1 = 'css/global.css?v=1.2'.match(fileExtensionPattern)[0];
console.log(ma1);
// returns .css
var ma2 = 'index.html?a=param'.match(fileExtensionPattern)[0];
console.log(ma2);
// returns .html
var ma3 = 'default.aspx?'.match(fileExtensionPattern)[0];
console.log(ma3);
// returns .aspx
var ma4 = 'pages.jsp#firstTab'.match(fileExtensionPattern)[0];
console.log(ma4);
// returns .jsp
var ma5 = 'jquery.min.js'.match(fileExtensionPattern)[0];
console.log(ma5);
// returns .js
var ma6 = 'file.123'.match(fileExtensionPattern)[0];
console.log(ma6);
// returns .123
Test page.
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