open (FILE, "> redo-output.txt") or die "Error: $!";

foreach (@lines)
{
  print FILE "$_\n";
}

close(FILE);
[download]

    # Since the submit button was pushed, we have to check to see if t
+he username

    # they typed exists.  $passwords is actually the hash we made earl
+ier, but since

    # we are using just ONE value we call our passwords hash as a scal
+ar: $passwords.

    # To lookup a hash key to see if it exists, you use: if (exists $h
+ash{"key"}) {}.
[download]

# Since the submit button was pushed, we have to check to see if the u
+sername
# they typed exists.  $passwords is actually the hash we made earlier,
+ but since
# we are using just ONE value we call our passwords hash as a scalar: 
+$passwords.
# To lookup a hash key to see if it exists, you use: if (exists $hash{
+"key"}) {}.
[download]

The lines in @lines still have their line endings attached, so when you print them with a newline you get doublespacing. Make that,

for (@lines) {
    print FILE $_;
}
[download]

or just, print FILE @lines; You also could chomp @lines to remove the previous line ends - useful if you need to translate them.

After Compline,
Zaxo

The elements of @lines has newlines. You either need to chomp them:

chomp(my @lines = <FILE>)

In which case you print them with:

print FILE for @lines;

# or, to be more verbose

foreach my $line (@lines) {
    print FILE $line
}
[download]




Or, you can leave off the chomp, and use the loop:

print FILE "$_\n" for @lines;

# or, to be more verbose

foreach my $line (@lines) {
    print FILE "$line\n";
}
[download]




Either you've removed the newlines or you haven't, your foreach loop has to match.

Of course, if this is all you're doing with @lines it'd be much simpler, and more kind to memory, to just read and write at the same time:

print OUTPUT_FILE while <INPUT_FILE>;

# or, to be more verbose

while ($line = <INPUT_FILE>) {
    # manipulation of $line goes here.
    print OUTPUT_FILE $line;
}
[download]

perldoc -q 'entire file' covers this topic, 5.6.1's perldoc -q 'line in a file' helps to explain dealing with files, and 5.8.4's perldoc -q 'line in a file' tells you to use Tie::File.