"I read the IO::File documentation. While I understand that getlines is supposed to be used in list context, using it directly by chaining the methods is not mentioned in there and I'm wondering the safety of using such method."

File handles are scalars, so you can push them onto arrays like this:

push @all_handles, $fh;
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And pop them off like this:

my $fh = pop @all_handles;
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And you can loop through an array of filehandles like this:

for my $fh (@all_handles) {
   ...;  # do something with $fh
}
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And you can get a count of how many filehandles are in your array of filehandles like this:

my $count_filehandles = @all_handles;
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There is no need to mention any of the above in the IO::File documentation because this is simply how arrays work in Perl. The fact that they're arrays of filehandles is not significant - they could be arrays of integers, or XML documents, or whatever.

Similarly, there's no need to mention in the IO::File documentation that methods which return an object can be chained. That's just how method calls work in Perl (indeed, in most programming languages that support OO).