$ perl -Mstrict -Mwarnings -E '
    my $buf = q{aXa};
    while ($buf =~ /a/gp) {
        say q{pos($buf):};
        say pos($buf);
        say q{${^MATCH}:};
        say ${^MATCH};
    }
'
pos($buf):
1
${^MATCH}:
a
pos($buf):
3
${^MATCH}:
a