How can I hook into Perl’s print?

by

There are a number of built-ins that you can override (see perlsub). However, print is one of the built-ins that doesn’t work this way. The difficulties of overriding print are detailed at this perlmonk’s thread.

However, you can

  1. Create a package
  2. Tie a handle
  3. Select this handle.

Now, a couple of people have given the basic framework, but it works out kind of like this:

package IO::Override;
use base qw<Tie::Handle>;
use Symbol qw<geniosym>;

sub TIEHANDLE { return bless geniosym, __PACKAGE__ }

sub PRINT { 
    shift;
    # You can do pretty much anything you want here. 
    # And it's printing to what was STDOUT at the start.
    # 
    print $OLD_STDOUT join( '', 'NOTICE: ', @_ );
}

tie *PRINTOUT, 'IO::Override';
our $OLD_STDOUT = select( *PRINTOUT );

You can override printf in the same manner:

sub PRINTF { 
    shift;
    # You can do pretty much anything you want here. 
    # And it's printing to what was STDOUT at the start.
    # 
    my $format = shift;
    print $OLD_STDOUT join( '', 'NOTICE: ', sprintf( $format, @_ ));
}

See Tie::Handle for what all you can override of STDOUT’s behavior.

More Related Contents:

  1. Failing to install MIME::Base64 using cpan [closed]
  2. Declaring a 2D coordinate in Perl / C / C++ [closed]
  3. Why can’t Perl find my file that is in ClearCase?
  4. Difference of Two Arrays Using Perl
  5. How can I output UTF-8 from Perl?
  6. When should I use the & to call a Perl subroutine?
  7. What’s the difference between a hash and hash reference in Perl?
  8. Multiline search replace with Perl
  9. How do I “use” a Perl module in a directory not in @INC?
  10. How can I process options using Perl in -n or -p mode?
  11. How can I combine hashes in Perl?
  12. Why do my Perl tests fail with use encoding ‘utf8’?
  13. What is the difference between my and local in Perl?
  14. Why does my Perl script exit with 137?
  15. ImageMagick Command-Line Option Order (and Categories of Command-Line Parameters)
  16. Perl Dereferencing Syntax
  17. How to extrace pg_backend_pid from postgresql in shell script and pass it to another process?
  18. Perl read line by line
  19. What is the difference between Perl’s ( or, and ) and ( ||, && ) short-circuit operators?
  20. How do I change, delete, or insert a line in a file, or append to the beginning of a file in Perl?
  21. How can I install a specific version of a set of Perl modules?
  22. What is the difference between `$this`, `@that`, and `%those` in Perl?
  23. Obtain a switch/case behaviour in Perl 5
  24. How do I extract the domain out of an URL?
  25. Why does $foo->{bar} autovivify but %$foo doesn’t?
  26. How can I extract text from a PDF file in Perl?
  27. Local and Global variables in perl
  28. How do I retrieve the terminal width in Perl?
  29. How to make DateTime::Duration output only in days?
  30. How do I tell CPAN to install all dependencies?

Leave a Comment