How Can I Store a File Handle in a Perl Object and how can I access the result? - perl

Question

I wanted to store a file handle in a Perl Object. Here is how I went about it.
sub openFiles {
my $self = shift;
open (my $itemsFile, "<", "items.txt") or die $!;
open (my $nameFile, "<", "FullNames.txt") or die $!;
$self->{itemsFile} = $itemsFile;
$self->{nameFile} = $nameFile;
return $self;
}
Then I'm looking to access some information from one of these files. Here is how I go about it.
sub getItemDescription {
my $self = #_;
chomp(my $record = $self->{itemsFile});
return $record;
}
I attempt to access it in another procedure as follows:
print "Test 3: $self->getItemDescription()\n";
My questions are as follows:
Is the way I'm saving the file handle in the object correct? If not, how is it wrong?
Is the way I'm reading the lines of the file correct? If not, how can I get it right?
Finally, is the way I'm printing the returned object correct?
This is really important to me. If there is any way that I can improve the structure of my code, i.e. making a global variable for file handling or changing the structure of the object, please let me know.

Answer 1

Is the way I'm saving the file handle in the object correct?
Yes.
Is the way I'm reading the lines of the file correct?
No. That just assigns the file handle. One reads a line from the file using the readline operator.
One would normally use the <...> syntax of the readline operator, but <...> is a shortcut for both readline(...) and glob(qq<...>), and Perl thinks <$self->{itemsFile}> is short for glob(qq<$self->{itemsFile}>). You have to use readline specifically
my $record = readline($self->{itemsFile});
chomp($record) if defined($record);
or do some extra work
my $fh = $self->{itemsFile};
my $record = <$fh>;
chomp($record) if defined($record);
(Note that I don't call chomp unconditionally since readline/<> can return undef.)
Finally, is the way I'm printing the returned object correct?
I presume you mean returned string, as in the string returned by getItemDescription. The catch is, you never actually call the method. ->getItemDescription() has no meaning in double quoted string literals, even after a variable. You need to move $self->getItemDescription() out of the double quotes.
You also fail to check if you've reached the end of the file.

Answer 2

You are close.
To read a record (line) from a filehandle, you use the builtin readline function or the <...> operator AFTER you assign the filehandle to a "simple scalar" (see edit below).
chomp(my $record = readline( $self->{itemsFile} );
my $fh = $self->{itemsFile};
chomp(my $record = <$fh>);
There is also a bug in your getItemDescription method. You'll want to say
my ($self) = #_;
instead of
my $self = #_;
The latter call is a scalar assignment of an array, which resolves to the length of the array, not the first element of the array.
EDIT: <$self->{itemsFile}> and <{$self->{itemsFile}}> do not work, as perlop explains:
If what's within the angle brackets is neither a filehandle nor a simple scalar variable containing a filehandle name, typeglob, or typeglob reference, it is interpreted as a filename pattern to be globbed, and either a list of filenames or the next filename in the list is returned, depending on context. This distinction is determined on syntactic grounds alone. That means <$x> is always a readline() from an indirect handle, but <$hash{key}> is always a glob(). That's because $x is a simple scalar variable, but $hash{key} is not--it's a hash element. Even <$x > (note the extra space) is treated as glob("$x "), not readline($x).

Answer 3

The openFiles piece is correct.
The errors occur primarily getItemDescription method.
First as previously mentioned my $self = #_; should be my ($self) = #_;.
However, the crux of the question is solved in the following fashion:
Change chomp(my $record = $self->{itemsFile}); to two lines:
$file1 = $self->{itemsFile};
chomp(my $record = $file1);
To clarify you must (in my experience and I tried all the solutions suggested) use a scalar value.
Finally, see the last two paragraphs in ikagami's answer.