Use <code></code> tags around Perl code to avoid problems with <, >, and square brackets.

I recommend using the Tie::File CPAN module since otherwise you have to create a temporary file, copy the original file to it with your changes, and then rename the temporary file to replace the original file.

use Tie::File;

sub loadmeal {
my($meal) = $_[0];
tie @meals, 'Tie::File', "/home/shaolin/public_html/monkmeals.txt" or 
+die ...;
for (@meals) {
    s/leeming=.*/leeming=$meal/
}
untie @meals;
[download]

You may also want to consider using a database (such as DBD::SQLite) instead of a plain text file depending on how many monks you have and how often you will be updating their meal choices. Manipulating plain text files in this fashion doesn't scale well.