java.util.regex.Pattern与在线regex调试器不同

Question

I'm working with some regex for a program, I want the program to detect a certain exe, called gruell[something].exe

So I ended up with the following regex:

gruell.*\.exe[^\.]

After testing on both these sites my test cases are detected properly

• https://regex101.com/
• https://regexr.com/

My test set: (and what should fail and pass)

• gruell-Core.exe [PASS]
• Gruell.exe [PASS]
• gruell_x64.exe [PASS]
• Gruell_x64-core.exe [PASS]
• grull.exe [FAIL]
• gruell_____.exe [PASS]
• gruell_installer.msi [FAIL]
• gruell.html [FAIL]
• .gruell.exe.398sn [FAIL]
• gru-ell.exe [FAIL]

When I run this on my machine using the java.util.regex.Pattern it will not find anything, eventhough the folder I told it to scan contains both:

• gruell.exe
• .gruell.exe.398sn

Now the intersting part is is when I remove [^.] it will detect, however, it detects the .gruell.exe.398sn aswell, which is what I don't want.

Code in question:

File f = new File("G:\\dev\\gruell");
recursive_scan(f);

The function:

for (file : location.listFiles())
{
    if (file.isDirectory)
    {
         recursive_scan(file)
    }
    else
    {
         Pattern pattern = Pattern.compile("gruell.*\\.exe[^\\.]", Pattern.CASE_INSENSITIVE);
         if (pattern.matcher(file.name).find())
         {
              System.out.println("FOUND: " + file.name);   
         }
     }
 }

Answer 1

After testing on both [regex101 and RegExr] my test cases are detected properly

That seems unlikely, since your pattern is indeed faulty, not only in Java's Regex dialect but also in the ones tested by those sites. The only plausible explanation I see is that you were not actually testing the cases you think you were. For example, your test inputs may have had trailing spaces or newlines.

Which brings me to the problem with your pattern. As you already observe,

Now the intersting part is is when I remove [^.] it will detect,

That's because that sub-expression matches a character (different from . ). Your overall pattern therefore indeed does not match "gruell-Core.exe" because there is no character after the .exe . Try matching "gruell-Core.exee" instead.

If you want your matches to end with .exe , then anchor your pattern instead: gruell.*\\.exe$

Answer 2

Alright thanks to the site provided by John Bollinger https://www.regexplanet.com/advanced/java/index.html I was able to find out 2 things that were wrong here.

First off I had to use:

 pattern.matcher(file.name).matches()

Instead of what I had:

 pattern.matcher(file.name).find()

And second off I had to remove [^.] from the end of the String.

From:

"gruell.*\\.exe[^.]"

To:

"gruell.*\\.exe"