I highly recommend reading the entry in the perldocs on open (perldoc -f open) and in the section on perlipc.

You can "open" system commands to a pipe by something like

open($fh, "command |") or die "command wouldn't run...because $!\n";
@output = <$fh>;
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In your case, you could write something like this:

my $command = "/usr/local/mysql/bin/mysql -u anonymous " .
              "-h my.database.org ".
              "--execute='show databases'";
open($fh, "$command |") or die "Could not execute $command because $!\
+n";
@results = <$fh>;
@results = grep { /$temp_choice/} @results;
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or (reading the output a line at a time, vs slurping it up)

while(<$fh>)
    {
     do_something if /$temp_choice/;
    }
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Note that this was not tested (I don't have mysql on my system) but it is syntactically correct.