Regex that matches files with two or more unique extensions

October 2, 2023

I am trying to create regex that matches files with two or more extensions, but I want to ignore duplicate extensions.

Examples of results I want:

videogame.exe.exe     - Don't match
unknown.pdf.exe       - Match
Resume.doc.docx       - Match
SalesNumbers.pdf.pdf  - Don't Match
summary.pdf.docx      - Match

Currently I have the following regex:

(\.\w+)(?!\1)\.\w+

This almost works. However, if the second extension contains the first I don’t get a match. The following examples do not provide matches, but I want them to.

Resume.doc.docx
text.exe.exe1

>Solution :

This regex, using word boundary:

(\.\w+)(?!\1\b)\.\w+
            ^^

(\.\w+)(?!\1$)\.\w+
            ^

Online Demo

The regular expression matches as follows:

Node	Explanation
`(`	group and capture to \1:
`\.`	.
`\w+`	word characters (a-z, A-Z, 0-9, _) (1 or more times (matching the most amount possible))
`)`	end of \1
`(?!`	[look ahead](https://perldoc.perl.org/perlre#Lookaround-A ssertions) to see if there is not:
`\1`	what was matched by capture \1
`\b`	the boundary anchor between a word char (\w) and something that is not a word char anchor
`)`	end of look-ahead
`\.`	.
`\w+`	word characters (a-z, A-Z, 0-9, _) (1 or more times (matching the most amount possible))