# Read the total content of a file. With or without '<'
open(FIL,"<$filename") || die "Cannot open $filename for reading: $!";
my @data = <FIL>;
close(FIL);

# Read a file line by line. Again with or without '<'
open(FIL,"<$filename") or die "Cannot open $filename for reading: $!";
while (my $data = <FILE>) {
  ## statements
};
close(FIL);

# Create a file and write a line of data.
# NOTE: If the file already exists it will be OVERWRITTEN
my $data = "A line of text";
open(FIL,">$filename") || die "Cannot create $filename for writing: $!";
print FILE "$data\n";
close(FIL);

# Append a line of data to a file. Creates the file if it does not exist.
open(FIL,">>$filename") || die "Cannot open $filename for appending: $!";
print FILE "$data\n";
close(FIL);