Question

please look at the following code first.

#! /usr/bin/perl
package foo;

sub new {

    my $pkg = shift;
    my $self = {};
    my $self->{_fd} = undef;
    bless $self, $pkg;

    return $self;
}

sub Setfd {

    my $self = shift;
    my $fd = shift;
    $self_->{_fd} = $fd;
}

sub write {

    my $self = shift;
    print $self->{_fd} "hello word";
}

my $foo = new foo;

My intention is to store a file handle within a class using hash. the file handle is undefined at first, but can be initilized afterwards by calling Setfd function. then
write can be called to actually write string “hello word” to a file indicated by the file handle, supposed that the file handle is the result of a success “write” open.

but, perl compiler just complains that there are syntax error in the “print” line. can anyone of you tells me what’s wrong here? thanks in advance.

Answer 1

You will need to put the $self->{_fd} expression in a block or assign it to a simpler expression:

    print { $self->{_fd} } "hello word";

    my $fd = $self->{_fd};
    print $fd "hello word";

From perldoc -f print:

Note that if you’re storing FILEHANDLEs in an array, or if you’re using any other expression more complex than a scalar variable to retrieve it, you will have to use a block returning the filehandle value instead:

print { $files[$i] } "stuff\n";
print { $OK ? STDOUT : STDERR } "stuff\n";