a hashtag
Matches a hashtag. It finds the match anywhere inside the text. There is 1 capture group.
Pattern
/(?:^|\s)#([a-z0-9_]+)/i- Match scope
- anywhere inside the text
- Capture groups
- 1
- Flags
- i · ignore case
- What it catches in the first example
- #cats
Try it yourself
Type any text and the parts this expression catches are highlighted. It runs in your browser and is never sent anywhere.
#cats
love #cats
2 matches
Examples that match
- #cats
- love #cats
Examples that do not match
- a#cats
- #
Other expressions in this group
"[^"\\]*(?:\\.[^"\\]*)*"text inside double quotes'[^'\\]*(?:\\.[^'\\]*)*'text inside single quotes\[([^\]]+)\]\(([^)]+)\)a Markdown link^#{1,6}\s+.+$a Markdown heading line(?:^|\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 URLHow 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 a hashtag?
(?:^|\s)#([a-z0-9_]+), with the i flag.
Q. Which strings match?
Text like #cats matches; text like a#cats 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.