#!perl -w
use strict;

sub my_print(@) {
    my @stuff = @_;
    print STDOUT time,": @stuff\n";
}

*print = *my_print;

print "Hello World!";
[download]

the warning message isn't useful in this case but if I change it to &print = &my_print; it prints...

Can't modify non-lvalue subroutine call at C:\Perl\scripts\newprint.pl
+ line 8.
991047768:
[download]

can this be made to work?

larryk

"Argument is futile - you will be ignorralated!"

Certain perl built-ins can be overriden and others can't. For a discussion on this, see this node. The following code shows one way to override a built-in:
Read more... (3 kB)

print filterText("Here's some text!");
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A search and replace and you are away. Any other solution seems likely to be more complex. You could for instance redirect STDOUT to a file and fork a second process to filter then print data as it arrives in this file. Seems overly complex though.

tachyon

Of course, you're still probably best off dividing it into 2 parts, a file containing the module IO::SubHandle: (properly located) and the main program.

#!/usr/local/bin/perl -w

package IO::SubHandle;

use strict;

sub TIEHANDLE {
  my $class = shift;
  local *FH = shift;
  my $sub = shift;

  bless { handle => *FH{IO}, routine => $sub }, $class;
}

sub PRINT {
  my $self = shift;
  my $fh = $self->{handle};
  print $fh ($self->{routine}->(@_));
}

# Not clear how to handle this!
sub PRINTF {
  my $self = shift;
  my $fmt = shift;
  $self->PRINT(sprintf($fmt => @_));
}


package main;

use IO::SubHandle;

sub filterText {
  ("Filter [@{[scalar @_]}]: ", @_);
}

print "This is your normal STDOUT\n";

tie *STDOUT, 'IO::SubHandle' => *STDOUT, \&filterText;

print "This is your filtered STDOUT\n";
print STDOUT "This also gets filtered...\n";
print STDERR "STDERR is safe...\n";
printf STDOUT "PRINTF(pi = \%g) tied too (but #args different)\n", 3.1
+4159;
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Depending on what operations you perform, you may need to tie some more methods! Note also how the printf tie probably isn't implemented "correctly"; you'll need to define precisely what it should do, then you can do it.