Or you could use the -command option to pass arguments to a named subroutine. TMTOWTDI. Also note how $i is used as the loop variable.

...
my @buttons;
for my $i (0..5){
    push @buttons,
        $mw->Button(
            -text => $row[$i],
            -command => [ \&buttonpress, $row[$i] ],
            )->pack;
}

sub buttonpress{
    my $btn = shift;
    print "button $btn pressed\n";
}
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