File extension is in extensions list

From Rosetta Code
File extension is in extensions list is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Given a file name and a list of extensions (including the dot), tell whether the file's extension is in the extensions list. The check should be case insensitive. The file might not have an extension.

Haskell

<lang Haskell> import Data.List import qualified Data.Char as Ch

toLower :: String -> String toLower = map Ch.toLower

isExt :: String -> [String] -> Bool isExt filename extensions = any (`elem` (tails . toLower $ filename)) $ map toLower extensions </lang>

The code defining isExt could be done point free: <lang Haskell> isExt filename = any (`elem` (tails . toLower $ filename)) . map toLower </lang>

Overcoming the one-liner urge on behalf of being more comprehensible would give: <lang Haskell> isExt filename extensions = any (`elem` allTails) lowerExtensions 

                           where allTails = tails . toLower $ filename

lowerExtensions = map toLower extensions </lang>


Perl 6

<lang perl6>my @ext = < .c .o >;

for < foo.C foo.zkl foo foo. > { 

   when / :i @ext $ / { say "$_\t$/ is in the list" }
   when / '.' \w* $ / { say "$_\t$/ is not in the list" }
   default            { say "$_\t (has no extension)" }

}</lang>

Output:
foo.C	.C is in the list
foo.zkl	.zkl is not in the list
foo	 (has no extension)
foo.	. is not in the list

Python

<lang Python> import os

def isExt(filename, extensions): 

   return os.path.splitext(filename.lower())[-1] in [e.lower() for e in extensions]

</lang>

REXX

Programming note:   extra code was added to:

  • display some error/warning messages
  • handle the case of the filename having a path
  • handle the case of different types of path separators
  • handle the case of the filename having no file extension
  • handle cases of the filename ending in a period
  • handle cases of the filename ending in multiple periods

<lang rexx>/*REXX program displays if a filename has a known extension (per a list)*/ extensions='.bat .cmd .com .dat .dll .exe .ini .jpg .jpeg .log .sys .txt' 

                                      /* [↑]  above would be some EXTs.*/

parse arg fn /*get the filename from the C.L. */ fn=strip(fn) /*remove any superfluous blanks. */ if fn== then exit /*No fn specified? Then exit.*/ afn=translate(fn,'/',"\") /*handle both versions of pathSep*/ afn=substr(fn,lastpos('/',afn)+1) /*pick off the filename from path*/ p=lastpos('.',afn) /*find the last position of a dot*/ if p==0 | p==length(afn) then do /*no dot or dot is at end of name*/ 

                              say 'Filename ' fn " has no extension."
                              exit
                              end

ft=substr(afn,p) /*pickoff the fileType (fileExt).*/ upper ft extensions /*uppercase a couple of REXX vars*/ if wordpos(ft,extensions)==0 then _='an unknown' 

                             else _= 'a known'

say 'Filename ' fn "has" _ 'extension.'</lang>

Ruby

<lang ruby>extensions = [".c",".o",""] ["foo.C","foo.zkl","foo","foo."].each{|f| p extensions.include?( File.extname(f).downcase )} </lang>

Output:
true
false
true
true

Scala

<lang Scala> def isExt(fileName: String, extensions: List[String]): Boolean = { 

   extensions.map { _.toLowerCase }.exists { fileName.toLowerCase endsWith _ }

} </lang>

zkl

<lang zkl>var exts=T(".c",".o",""); fcn hasExtension(fname){ exts.holds(File.splitFileName(fname)[3].toLower()) } T("foo.C","foo.zkl","foo","foo.").apply(hasExtension).println();</lang>

Output:
L(True,False,True,True)
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