php regular expression how do i get last part of a string

I hav开发者_JAVA百科e a file whatever_files_123456.ext. I need to read just the number after the last underscore in a filename. Filename can contain many underscores. I only care about the number after the last underscore and before the .ext. In this case it's 123456

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No need for regular expressions:

$parts = explode('_', $filename);
$num = (int)end($parts);

This will explode the filename into parts based on the underscore. Then convert the last item to an int value (quick way to remove the extension).

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Try this:

preg_replace("/.*\_(\d+)(\.[\w\d]+)?$/", "$1", $filename)

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If the number is always at the end, it could be faster to use explode to split the name up by underscores, grab the last item from the list, and strip off the ".ext". Like:

<?php
  $file = 'whatever_files_123456.ext';
  $split_up = explode('_', $file);
  $last_item = $split_up[count($split_up)-1];
  $number = substr($last_item, 0, -4);

But, if you do want to use preg_match, this would do the trick:

<?php
  $file = 'whatever_files_123456.ext';
  $regex = '/_(\d+).ext/';
  $items = array();
  $matched = preg_match($regex, $file, $items);
  $number = '';
  if($matched) $number = $items[1];

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If the number always appears after the last underscore you should use:

$underArr=explode('_', $filename);
$arrSize=count($underArr)-1;
$num=$underArr[$arrSize];
$num=str_replace(".ext","",$num);

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$pattern = '#.*\_([0-9]+)\.[a-z]+$#';
$subject = 'whatever_files_123456.ext';
$matches = array();

preg_match($pattern, $subject,$matches);

echo $matches[1]; // this is want u want