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Filtering files with regular expression

Posted on 2003-10-21
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Last Modified: 2006-11-17
I'm trying to filter files in a directory.
To do so, I need a function using regular expression that can accept 3 parameters:
a filename, a prefix and an extension and returns true (match) or false (no match)

My code at this moment is:

<?php
function CheckPattern($filename, $prefix, $ext) {
  $testExp = "^".$prefix."([\.\+\-\@\w\d])*\.".$ext."$";
  return ($testExp, $filename) );
}
$sPref = "ABC";
$sExt = "xml";
$file = "ABC-123asq.xml";
 if (CheckPattern($file, $sPref, $sExt)) {
     echo "Its a match";
 } else {
     echo "No match";
 }
?>

It should return a match in this example, but it doesn't :-(
I'm stucked on this.

Any help?
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Question by:itamar
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4 Comments
 
LVL 14

Accepted Solution

by:
ThG earned 500 total points
ID: 9593952

function CheckPattern($filename, $prefix, $ext) {
 $testExp = "/^".$prefix."([\.\+\-\@\w\d])*\.".$ext."$/";
 return preg_match($testExp, $filename);
}

this is your fixed function *BUT* it's very bad coding, because regexp have many metacharacters, so inserting a raw parameter into the regular expression might cause unexpected behaviour.
Guess what would happen if you enforce suffix:
".jpg"
that would match "Ajpg", "5jpg", "?jpg"
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LVL 4

Author Comment

by:itamar
ID: 9597985
Hi ThG,

I got your point.
But it is part of a bigger context.
Extensions are choosen from a list and prefix probably will be letters from A to Z (index)

Many thanks.

Itamar
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LVL 4

Author Comment

by:itamar
ID: 9598016
Hi again,

looking at your code I could see the difference is in "/^" and "$/"

As I'm PHP beginner could you explain why it's necessary as a bonus ;-))

Thanks again
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LVL 14

Expert Comment

by:ThG
ID: 9598282

OK :-)
That's not php related, that's the basic syntax for regular expressions. A regular expression is anclosed between two delimiters, no matter which they are, but you SHOULD use "/"
you were probably getting an error related to missing delimiter "^", because it thought you were using "^" and "^" as delimiters, which is totally wrong.
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