Escape path separator in a regular expression

I need to write a regular expression that finds javascript files that match

<anypath><slash>js<slash><anything>.js

For example, it should work for both :

• c:\mysite\js\common.js (Windows)
• /var/www/mysite/js/common.js (UNIX)

The problem is that the file separator in Windows is not being properly escaped :

pattern = Pattern.compile(
     "^(.+?)" + 
     File.separator +
     "js" +
     File.separator +
     "(.+?).js$" );

Throwing

java.util.regex.PatternSyntaxException: Illegal/unsupported escape sequence

Is there any way to use a common regular expression that works in both Windows and UNIX systems ?

From stackoverflow Guido

• Does Pattern.quote(File.separator) do the trick?

  EDIT: This is available as of Java 1.5 or later. For 1.4, you need to simply escape the file separator char:

  "\\" + File.separator
  

  Escaping punctuation characters will not break anything, but escaping letters or numbers unconditionally will either change them to their special meaning or lead to a PatternSyntaxException. (Thanks Alan M for pointing this out in the comments!)

  Guido : Great, what a pity it is only available since Java 1.5+ (I still need it to work in 1.4)
  From Tomalak

• Can't you just use a backslash to escape the path separator like so:

  pattern = Pattern.compile(
       "^(.+?)\\" + 
       File.separator +
       "js\\" +
       File.separator +
       "(.+?).js$" );
  

  From Peter van der Heijden

• Why don't you escape File.separator:

  ... +
  "\\" + File.separator +
  ...
  

  to fit Pattern.compile requirements? I hope "\/" (unix case) is processed as a single "/".

  From gimel

• I've tested gimel's answer on a Unix system - putting "\\" + File.separator works fine - the resulting "\/" in the pattern correctly matches a single "/"

  From Alnitak

• Is there any way to use a common regular expression that works in both Windows and UNIX systems ?

  Yes, just use a regex that matches both kinds of separator.

  pattern = Pattern.compile(
      "^(.+?)" + 
      "[/\\\\]" +
      "js" +
      "[/\\\\]" +
      "(.+?)\\.js$" );
  

  It's safe because neither Windows nor Unix permits those characters in a file or directory name.

  From Alan Moore