open (MYFILE, "< $filename") or die "Failed to open $filename: $!";
@rows = <MYFILE>;
close (MYFILE);

foreach $row (@rows) {
    # do something to $row
}

##</code><code>##

open (MYFILE, "< $filename") or die "Failed to open $filename: $!";
while (<MYFILE>) {
    # do something with $_
}
close (MYFILE);