the extension of a file name
Matches the extension of a file name. It finds the match anywhere inside the text. There is 1 capture group.
Pattern
/\.([a-z0-9]+)$/i- Match scope
- anywhere inside the text
- Capture groups
- 1
- Flags
- i · ignore case
- What it catches in the first example
- .jpg
Try it yourself
Type any text and the parts this expression catches are highlighted. It runs in your browser and is never sent anywhere.
photo.jpg
a.tar.gz
1 match
Examples that match
- photo.jpg
- a.tar.gz
Examples that do not match
- photo
- archive.
Other expressions in this group
(?:^|\s)@([a-z0-9_]{2,})an @ mention[?&]([^=&]+)=([^&]*)a query parameter in a URLhttps?://[^\s<>"]+a URL sitting inside ordinary text^https?://([^/:?#]+)just the domain out of a URL(?<=[a-z0-9])(?=[A-Z])the seam between words in camelCase_([a-z])the letter that follows an underscore-([a-z])the letter that follows a hyphen(?:^|,)("(?:[^"]|"")*"|[^,]+)one comma-separated fieldHow to read this
- With ^ and $ around it, the whole string must match; without them the match can sit anywhere. Always anchor an expression you use for validation.
- Round brackets ( ) capture what they wrap. When you only need grouping, write (?: ) so the numbering of later groups does not shift.
- Every expression here is checked against its examples. Even so, "looks like an email" and "is a real inbox" remain different questions.
- Nested open-ended repeats such as (a+)+ can blow up on certain inputs. Look for that shape before pasting someone else’s expression into your code.
Frequently asked questions
Q. What is the regex for the extension of a file name?
\.([a-z0-9]+)$, with the i flag.
Q. Which strings match?
Text like photo.jpg matches; text like photo does not.
Q. Does the whole string have to match?
No. It finds the part anywhere inside the text. Add ^ and $ around it if you want a whole-string check.
Q. How do I use what it caught?
There is one capture group, so you can read them from match[1] onwards.