CODEWITHSUNDEEP
regexclojure
R X
R X

Reputation: 281

Clojure multiline regular expression

I'm trying to test a string for a basic html pattern and although I use the m (multiline) modifier it only works when the string is a 1-liner

(re-find #"(?im)^<html>.*<body>.*</body>.*</html>" c))

Fails:

"<html>   <body>   sad   </body> 
     </html>"

Works:

"<html>   <body>   sad   </body>      </html>"

What am I doing wrong?

Upvotes: 17

Views: 5636

Answers (2)

zb226
zb226

Reputation: 10500

Disclaimer: I'm not a Clojure programmer, but I think this problem is independent of the language.

When multi-line mode is enabled, the interpretation of the caret ^ and the dollar $ changes like this: Instead of matching the beginning and end of the entire input string, they match the beginning and the end of each line in the input string. This is - as far as I can see - not what you want/need.

What you want is for your .*s to match newlines (what they don't do by default) and this can be done by enabling the single-line mode (aka dot-all mode). So this means:

(re-find #"(?is)^<html>.*<body>.*</body>.*</html>" c))

You can also verify this on RegExr.

Upvotes: 21

Matt Fenwick
Matt Fenwick

Reputation: 49085

You need to use the (?s) "dotall mode" switch.

Example:

user=> (re-find #"\d{3}.\d{3}" "123\n456")    
nil

user=> (re-find #"(?s)\d{3}.\d{3}" "123\n456")
"123\n456"

The (?m) switch is deceptively named -- it changes what the ^ and $ anchors do, allowing them to also match start-of-line and end-of-line, respectively -- which is not want you want.

Upvotes: 16

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