When opening a file you can either specify the filehandle, or you can provide an undefined scalar (or existing reference) - which will then hold an anonymous reference to a newly created filehandle.

Typically one opens file lie this:

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

print SOME_FH "Test\n";
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But it's also ok to do this

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

print $fh "Test\n";
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In the code you listed the programmer chose the second option, but instead of declaring a lexical variable to keep the filehandle in, he uses the variable named $XFORM_FILE in the AB package.

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