In regular expression, the meta-character Digit "\d" is used to match any numeric character.

    <?php
    $name = "23451-9875";
    if (preg_match("/\d{5}(-\d{4})?$/", $name))
     echo "Regex Pattern matches!";
    else 
     echo "Regex Pattern not matched!";
    ?>

    Pattern matches! 

In the above example the pattern "\d{5}(-\d{4})?$/", first part "d{5}" matches a string with exactly "5" digits and the second part is a sub pattern "(-\d{4})?$" matches a "-" along with exactly "4" digits, since the "?" is used for the subpattern it may or may not occur, "$" specifes to check the subpattern at the end of the string.

    #! C:\programfiles\perl\bin\perl
    print "content-type: text/html\n\n";
    $name= "-23";
    if ($name =~ m/^\d+$/)
      {print "It's a positive number!";} 
    else 
      {print "It's a negative number!";}

    It's a negative number!

In the above example a positive number is checked for to match, since a negative number is given the condition is false, so it print's the message.