use Filter::Handle;

my $logfile = "program.log";
open(LOG, ">", $logfile) or die "Cannot write to '$logfile': $!";
Filter(
 \*STDOUT, sub {
    print LOG @_;
    return @_;
  }
);
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UPDATE
To answer the second question, I suggest reading Suffering from Buffering by Dominus.

Have a look at IO::Tee.

{
   use Tie::Handle::StdOutAndFile;
   local *STDOUT;
   tie(*STDOUT,'Tie::Handle::StdOutAndFile','file.txt') or die "Aaah $
+!\n";
   print "whatever";
}
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______crazyinsomniac_____________________________ Of all the things I've lost, I miss my mind the most. perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"

i rolled my own sub a long time ago, when i was pretty new to perl, and wanted the excersize. i dug it up for you:

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

use strict;
use FileHandle;
use Getopt::Std;
use vars qw($opt_n);

die( "Error: No arguments passed.\n" ) unless( $#ARGV >= 0 );

my $text = pop @ARGV;

die("no opts\n") unless getopts('n');

unless ( $opt_n ) {
    print $text."\n";
}

while ($ARGV[0]) {
    $_ = shift;
    my $FH = new FileHandle ">>$_" or die( "oops! $!\n" );
    print $FH $text."\n";
    close( $FH );
}
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mprint($::AUDITLOG, $::BUILDLOG, " ** dbcfg.tmp file in $::BUILDPATH n
+ot found * Run Aborted!!!");
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~Particle

#!/usr/local/bin/perl

open (OUT, ">/tmp/out.file");

$fh = select (OUT);
$| = 1;
select($fh);

print STDOUT "Hello!\n"; # prints to stdout
print "Hello!\n";        # prints to $fh = /tmp/out.file as no filehandle has been stated

The return value from select() is the previously selected filehandle. Therefore $fh is actually STDOUT (i.e. the filehandle that was hot before the select), so when you select($fh) you are back with STDOUT as your Currently-Selected-Filehandle. Does that make sense?

-Blake

open my $foo, ">>bar" || die "Can't write to bar : $!\n";

sub print2 {
    my $fh = shift;
    print STDOUT "$_[0]";
    print $fh "$_[0]";
}

### needs a comma, unlike print()
print2 $foo, "Hello, world!\n";
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