Re: monitor STDOUT in scalar

[btrott]

You should be able to inherit from Tie::Handle (part of the standard distribution) and override any methods you wish to define yourself:

    package MySTDOUT;
    use Tie::Handle;
    @ISA = qw/Tie::Handle/;

    sub TIEHANDLE {
        my $class = shift;
        bless {}, $class;
    }

    package main;
    tie *STDOUT, 'MySTDOUT';

For example, maybe you want to trap every call to STDOUT and prefix each argument with a string of your own:

    package MySTDOUT;
    use Tie::Handle;
    @ISA = qw/Tie::Handle/;

    sub TIEHANDLE {
        my $class = shift;
        bless {}, $class;
    }

    sub PRINT {
        my $self = shift;
        my $caller = caller;
        print STDERR map "$caller: $_", @_;
    }

    package main;
    tie *STDOUT, 'MySTDOUT';

    print "Foo";

Prints

    main: Foo

Take a look at the Apache module and Apache::Filter for some examples of tying STDOUT.

[Adam]

That is very cool! It also answers a question I asked some time ago, about Line Numbers. You could use this to put line numbers in your debug log:

    package MyDEBUGLOG;
    use Tie::Handle;
    @ISA = qw/Tie::Handle/;

    sub TIEHANDLE {
        my $class = shift;
        bless {}, $class;
    }

    {
        my $line = 0;
        sub PRINT {
            my $self = shift;
            ++$line;
            print DEBUGLOG map "$line: $_", @_;
        }
    }

    package main;
    tie *DEBUGLOG, 'MyDEBUGLOG';

    print DEBUGLOG "Foo";

Or so I would suspect. Very cool.

[btrott]

Well, not quite, because DEBUGLOG isn't opened for writing, for one thing, and for another, it's tied in a different package than when you're actually writing to it (main vs. MyDEBUGLOG).

And even if you do work out those issues, I think you'll have a problem with "Deep Recursion". You're writing to a tied filehandle, which invokes the PRINT method on your tied object, which... writes to the same tied filehandle. Hence recursion.

Check out my new Snippet, Filehandle Filter. With that you could do this:

    use Filter::Handle;

    local *DEBUG
    open DEBUG, ">debuglog" or die $!;

    my $f = Filter::Handle->new(\*DEBUG);
    print DEBUG "Foo";
    print DEBUG "Bar";

[Adam]

Cool, Thanks...