while (...) {
    if (/foo/) {
        FIRST {...; next}
    }
    ...
}

##</code><code>##

my @list = qw /foo bar foo/;
for my $x (1, 2) {
    for (@list) {
        if (/foo/) {  # Assume a 'once-only if'
            print "foo";
        }
     }
}