Typically one opens file lie this:

open SOME_FH, ">", "somefile" or die "Failed to open somefile. $!";

print SOME_FH "Test\n";
[download]

my $fh = undef;
open $fh, ">", "somefile" or die "Failed to open somefile. $!";

print $fh "Test\n";
[download]

You can read more about packages here

Thanks loads.. I did read the open docs but missed the meaning of not opened (i guess I scanned the doc rather than read)..

Also, I have never used
::
in an open statement so I don't know exactly what this means.

Somewhere in the file you are looking at there's might be either the statement use AB or package AB. See use and package.

--shmem

update - inserted "might", see follow-up. As imp correctly notes, a symbol table can but must not be created via a package or use statement.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

There might not be a use AB or package AB, the original programmer might just be using AB as a global variable namespace.

When faced with a problem like this, a good start would be to read the documentation for open. That says this about the return value from open:

Open returns nonzero upon success, the undefined value otherwise

So your code is called open, checking the return value and taking appropriate action if it fails.