DavidSzczesniak
1/12/2018 - 9:59 AM

Filehandles in a Scalar

Instead of a bareword, you can create a filehandle using a scalar variable. This makes things like passing a filehandle as a subroutine argument, storing them in arrays and hashes and controlling its scope, much easier.

scalar_filehandle.pl
content_copyfile_download
# Typically done with a lexical variable because that way, you can ensure to get a variable without a value
my $rocks_fh; # It's common practise to put '_fh' on the end of these to remember they are filehandles
open $rocks_fh, '<', 'rocks.txt'
  or die "Could not open rocks.txt: $!";

# Combine the two statements so you declare the lexical variable along with the open:
open my $rocks_fh, '<', 'rocks.txt';
or die "Could not open rocks.txt: $!";

# Once that variable is set up, you can use it the same way as the bareword version:
while(<$rocks_fh>) {
  chomp;
  ...
}

# Output filehandle example:
open my $rocks_fh, '>>', 'rocks.txt'
  or die "Could not open rocks.txt: $!";
foreach my $rock (qw(slate lava granite)) {
  say $rocks_fh $rock
}

print $rocks_fh "limestone\n";
close $rocks_fh;