PHP preg_match regex examples

PHP regex FAQ: Can you share some PHP regex examples using the PHP preg_match function?

For a recent PHP program I was writing, I experimented with the PHP preg_match function and some regular expressions, trying to get the behavior I was looking for. Now that they're working properly, I thought I'd share a few simple examples of my "PHP regex" preg_match examples/experiments.

PHP regex example 1: A string ending in a question mark

In this first PHP regex example I'm trying to match any sentence that ends in a question mark. In this example the "^" symbol means "beginning of line", the "$" means "end of line", and the ".*" part means "any number of any characters":

<?
$pattern = "/^.*\?$/";
$string = "this is good???";

$count = preg_match($pattern, $string);
print $count;
?>

PHP regex example 2: Non-alphanumeric keys pattern

In this second example I'm looking for every non-alphanumeric keyboard key that can be type:

<?
$pattern = "/[`'\"~!@# $*()<>,:;{}\|]/";
$string = "thi|sisatest";

$count = preg_match($pattern, $string);
print $count;
?>

Frankly, this probably wasn't a great approach, and I should have reversed the regex search pattern. I think what I was trying to do was only allow alphanumeric characters, and I probably would have been better looking for something like "0-9a-zA-Z", but this is still a decent example for other uses. I'll leave this other pattern approach as an exercise for the reader. :)

PHP regex pattern 3: preg_match for a PHP URI (GET request)

Okay, I just need to do some more preg_match work for a new PHP program I'm working on, and created the following test script for a preg_match pattern to test against a URI as part of testing the data I receive in a GET request. Here's the complete test script I just worked up:

<?php

# a php uri pattern match (for a php get request)
# look for anything other than these allowable characters
# A-Z, a-z, 0-9, _, ., -, +, ?, /, =
$pattern = "/[^A-Za-z0-9_\.\-\+\?\/=]/";
$string  = "?q=foo+a_b+a-z.java/foo/bar.cgi";

if (preg_match($pattern, $string))
{
  echo "string had bad characters in it";
}
else
{
  echo "no bad characters";
}

?>

As you can see from that code, there is a collection of characters I think should be valid in a PHP GET request, so I specify those, and then tell the pattern that anything other than these characters should trigger a match (with the ^ character as the first character in my pattern). In this way I can allow good URI and GET requests through, and reject other URIs, which may be attempts to hack the system.