stdout back to the normal ??

[iza]

hi :)

my code is

 open STDOUT, ">$file" || die "Cannot open file $file : $!";   
 system "diff $old_file $file";
 select(STDOUT); # Restore default print to STDOUT
 close(STDOUT);

but the default print is never ever restored to stdout (i mean, as long as the program runs !)
i don't know how to restore defaut print ... can anyone help ??

[jeffa]

Hi, this is straight from Dr. Stein's excellent Network Programming in Perl book:

print "redirecting STDOUT\n";
open (SAVEOUT, ">&STDOUT");
open (STDOUT, ">$file") or die "Can't open $file: $!";

#STDOUT is now redirected
system "diff $old_file $file";

open (STDOUT, ">&SAVEOUT");
print "STDOUT is back to normal!\n";

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)

[davis]

Hi, I think the problem is the open STDOUT. You're redirecting the output of STDOUT to $file, and in fact the select(STDOUT) doesn't acheive anything, because the default output handle is already STDOUT.
Another way around would be to open a read pipe from a system command, like this:

#!/usr/bin/perl -w

use strict;

my $output = "out.txt";

open(OUT, ">$output")
        or die "Couldn't open $output: $!\n";
open(IN, "date|")
        or die "Couldn't open date|: $!\n";
print OUT <IN>;
close(OUT);
close(IN);
print "This gets printed to stdout.\n";

There are, of course, other ways to do it, but that's something for some more experienced monks to attempt :).

[chromatic]

Is this better?

{
    local *NEWOUT;
    open(NEWOUT, "> $file") or die "Cannot open ($file): $!";
    my $oldfh = select(NEWOUT);
    # print some stuff here
    select($oldfh);
}

Of course, if you're going to run a system call, you might just use shell redirection to the file. There's more than one way to tame this camel. (Caveat added because I'm not sure redirecting STDOUT in a Perl parent will affect the non-Perl child.)