# open my $fh, '<', $file_path or die "unable to read $file_path"

# list context: every line goes in the array
my @all_lines = <$fh>;


# scalar context: just next line goes into a scalar (<> acts as an iterator here)
my $line = <$fh>;

# so to read a file one line at time:
while (defined( my $line= <$fh>)) {