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Asked: 2026-05-10T20:31:18+00:00

I need to write a regular expression that finds javascript files that match <anypath><slash>js<slash><anything>.js

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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 ?

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1 Answer

  1. 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!)

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