Extract file extension: Difference between revisions

;; Note that for a real implementation, Racket has a

;; `filename-extension` in its standard library, but don't use it here

;; since it requires a proper name (fails on ""), returns a byte-string,

;; and handles path values so might run into problems with unicode

;; string inputs.

(define (string-extension x)

(cadr (regexp-match #px"(\\.[[:alnum:]]+|)$" x)))

(define (string-extension/unicode x)

(cadr (regexp-match #px"(\\.(?:\\p{L}|\\p{N}|\\p{M})+|)$" x)))

(define examples '("picture.jpg"

"http://mywebsite.com/picture/image.png"

"myuniquefile.longextension"

"IAmAFileWithoutExtension"

"/path/to.my/file"

"file.odd_one"

""

;; Extra, with unicode

"café.png"

"file.resumé"

;; with unicode combining characters

"cafe\u0301.png"

"file.resume\u0301"))

(printf "Official task:\n")

(for ([x (in-list examples)])

(printf "~s ==> ~s\n" x (string-extension x)))

(printf "\nWith unicode support:\n")

(for ([x (in-list examples)])

(printf "~s ==> ~s\n" x (string-extension/unicode x)))

</lang>

<pre>Official task:

"picture.jpg" ==> ".jpg"

"http://mywebsite.com/picture/image.png" ==> ".png"

"myuniquefile.longextension" ==> ".longextension"

"IAmAFileWithoutExtension" ==> ""

"/path/to.my/file" ==> ""

"file.odd_one" ==> ""

"" ==> ""

"café.png" ==> ".png"

"file.resumé" ==> ""

"café.png" ==> ".png"

"file.resumé" ==> ""

With unicode support:

"picture.jpg" ==> ".jpg"

"http://mywebsite.com/picture/image.png" ==> ".png"

"myuniquefile.longextension" ==> ".longextension"

"IAmAFileWithoutExtension" ==> ""

"/path/to.my/file" ==> ""

"file.odd_one" ==> ""

"" ==> ""

"café.png" ==> ".png"

"file.resumé" ==> ".resumé"

"café.png" ==> ".png"

"file.resumé" ==> ".resumé"

</pre>