$re = '/^(?:0*)(\d+(\.(25|5|75))?)(?:0*)$/m';
$str = '1
01
1.25
01.25
0
0.25
0.50
0.5
0.750
000
0001.111
0001.5
.25
01234
';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php