Question

Basically, what I’m trying to do is search through a rather large PHP file, and replace any block of PHP code that includes the string “search_term” somewhere in it with some other code. I.e.

<?php
//some stuff
?>
<?php
// some more stuff
$str = "search_term";
// yes...
?>
<?php 
// last stuff
?>

should become

<?php
//some stuff
?>
HELLO
<?php 
// last stuff
?>

What I’ve got so far is

$string =~ s/<\?php(.*?)search_term(.*?)\?>/HELLO/ims;

This correctly matches the closest closing ?>, but begins the match at the very first <?php, instead of the one closest to the string search_term.

What am I doing wrong?

Answer 1

Generally, I don’t like to use non-greedy matching, because it usually leads to problems like this. Perl looks at your file, finds the first '<?php', then starts looking for the rest of the regexp. It passes over the first '?>' and the second '<?php' because they match .*, then finds search_term and the next '?>', and it’s done.

Non-greedy matching means that you have a regular expression that matches more things than you really want, and it leaves it up to perl to decide which match to return. It’s better to use a regular expression that matches exactly what you want to match. In this case, you can get what you want by using ((?!\?>).)* instead of .*? ((?!\?>) is a negative look-ahead assertion)

s/<\?php((?!\?>).)*search_term((?!\?>).)*\?>/HELLO/is;

If you expect multiple matches, you might want to use /isg rather than /is.

Alternatively, just split the file into blocks:

@blocks = split /(\?>)/, $string;
while (@blocks) {
    $block = shift @blocks;
    $sep = shift @blocks;
    if ($block=~/search_term/) {
        print "HELLO";
    } else {
        print $block, $sep;
    }
}