use strict;
use warnings;
use 5.016;

my $fname = 'data.txt';

open my $INFILE, '<', $fname
    or die "Couldn't open $fname: $!";

while (my $line = <$INFILE>) {
    chomp $line;
    #do something to $line;
}

close $INFILE
    or die "Couldn't close $fname: $!";