PHP half-copied Perl a lot. Another example is implementing arrays and hashes, but not as separate types. So you have odd behavior like the array sort functions sorting values but not renumbering keys because there's no distinction between an array and a map. Or copying Perl's string interpolation and concatenation operator but not its regular expression literals, so writing regexes in PHP requires an extra layer of escape sequences.
PHP requires escaping quotes and literal backslashes (i.e., backslashes not used for metacharacters or escaping other characters). For many cases, it doesn't affect anything, but it can turn into a bit of a nightmare if you're matching anything involving backslashes since you need four backslashes to match one literal backslash. Perl's regular expression literals are also nicer for things like splitting a long expression over multiple lines.
