Why do you close STDOUT. You can use select instead.
I don't see why you use seek in your code when you open one filehandle for input and one for output. If you whould have used +> instead, you would need the seek. (see perldoc perlopentut).

use POSIX;
use strict;

my $TRAP=POSIX::tmpnam();
print "TMPFILE is $TRAP\n";

open(TMPFILE, "+> $TRAP") or die $!;
select TMPFILE;
eval { print 'Waka Waka' };
seek(TMPFILE,0,0);
my $input=<INFILE>;
close(INFILE>;
select STDOUT;

print $input;
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This works fine for me.
---------------------------
Dr. Mark Ceulemans
Senior Consultant
IT Masters, Belgium

• mce As tilly says select only handles prints without a specified handle but not explicit STDOUT.

-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=2437">st<
+/A>)/'\$1/mg"
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#!/usr/bin/perl -lw
use POSIX;
my $TRAP = POSIX::tmpnam();
print STDERR "STDOUT= ".fileno(STDOUT);
close(STDOUT);
print STDERR "STDOUT= ".fileno(STDOUT);
open(STDOUT, ">$TRAP")  || die("$!: $TRAP"); #+> didn't work
eval "print 'Waka waka!'";
seek(STDOUT, 0, 0);
print STDERR "STDOUT= ".fileno(STDOUT);
close(STDOUT);
open(STDOUT, ">-");
print STDERR "STDOUT= ".fileno(STDOUT);
open(INPUT, "<$TRAP") || die("$!: $TRAP");
$chldoutput = <INPUT>;
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open(MYSTDOUT, ">&STDOUT");
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open(STDOUT, ">&MYSTDOUT");
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With that what you want to do can be done as:

use File::Temp qw(tempfile);

my $temp_fh = tempfile();
my $saved_fh = select($temp_fh);
eval "print 'Waka waka!'";
seek ($temp_fh, 0, 0);
select($saved_fh);
$text = join '', <$temp_fh>;
print "The text was '$text'\n";
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use File::Temp;
use Carp;

# Takes code to be evaled, supresses printing and returns
# the text that would have been printed.
sub eval_print_trap {
  my $code = shift;

  my $temp_fh = tempfile();
  my $saved_fh = select($temp_fh);
  eval($code);
  select($saved_fh);

  if ($@) {
    confess("Evaling \n'$code'\ngave error $@");
  }
  seek($temp_fh, 0, 0);
  wantarray ? <$temp_fh>: join '', $temp_fh;
}
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my $output = eval_print_trap("print 'Waka waka!'");
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Caveat programmer: Perl's select will only redirect prints to the default output from Perl code. You will not trap error output, and you will not trap any printing that comes within C code or other programs. Good luck if you plan to call system.

An alternative is to avoid the tmpfile altogether and tie an IO::Scalar for capturing the output. We can also localize STDOUT and STDERR (rather than select) and provide a simple __WARN__ sig handler to make up for some of the mentioned caveats:

    #!/usr/bin/perl -w
    use strict;
    use IO::Scalar;
    use Carp;

    my $out = eval_print_trap(<<'EOC');
        print "Hello World\n";
        print STDOUT "Hello again\n";
        print STDERR "stderr is here too\n";
        print "this uninit warning is captured:$a\n";
        warn "and explicit warnings as well";
        system(q|echo "Can't have everything!"|);
    EOC

    print "***\n$out***\n";
    print "done\n";

    sub eval_print_trap {
        my $code = shift;

        my $string;
        my $SH  = IO::Scalar->new_tie(\$string);

        {
            local *STDOUT = $SH;
            local *STDERR = $SH;
            local $SIG{__WARN__} = sub{print @_};
            eval($code);
        }

        if($@){
            confess "Evaling\n'$code'\ngave error $@";
        }
        return $string;
    }
    __END__
    ### could also have this at the end:
    seek($SH,0,0);
    wantarray ? <$SH> : $string;
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Yeah I should have mentioned I didn't want to use IO::Scalar; at least File::Temp is standard in 5.6.1 and there is a fall back which is always available.

-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=2437">st<
+/A>)/'\$1/mg"
[download]

tilly I am using File::Temp, that's where tmpnam comes from (with a fallback to POSIX).

I should point out that the code in the eval will be unknown, not wirtten by me no idea what's in it. Also, I have already dupped STDERR to STDOUT.

I would prefer to use tmpfile; even if I can't fallback then; but since I'm trying to *replace* STDOUT (for those who explicitly print to it, which as you pointed out select will do nothing about). But I as unable to dup the filehandle to STDOUT. I tried doing a

my $TRAP = tmpfile();
$no = fileno($TRAP);
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on it and opening as open(STDOUT, ">&$fileno"); as well as open(STDOUT, ">&=$fileno"); Neither of which worked so I figured I had to roll my own.

-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=2437">st<
+/A>)/'\$1/mg"
[download]

UPDATE: Clearly dupping STDERR it is not right, fixed that I am now trying to open STDERR to the same file as STDOUT in the same way (though one is > and the other is >>)

UPDATE 2: I should also note that I'd rather not use IO::Scalar as it's not standard even in 5.6.1. Maybe I'm just asking for too much? But it seems that the only thing preventing a reasonable solution is the warning about using the filehandles once. And I'd like to understand it before I do local $^W=0;

-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=3333">st<
+/A>)/'\$1/mg"
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a) yes I was able to get it to work with a double dup to save STDOUT (see b below) however I don't understand why I cannot recover STDOUT by one of:

open(STDOUT, '>-');
open(STDOUT, '>&=1');
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b)The folloing is similar to what you posted with some updates *but* if you run it with -w -Mstrict you get: Name "main::SAVE" used only once: possible typo

use POSIX;
local $/ = undef;
my $chldoutput;
my $TRAP = POSIX::tmpnam();

print "Gonna use $TRAP\n";
open(SAVE1, ">&STDOUT");
open(SAVE2, ">&STDERR");
close(STDOUT);
open(STDERR, ">$TRAP");
open(STDOUT, ">>$TRAP")  || die("$!: $TRAP"); #+> didn't work
eval "print STDERR 'Scary... ';print 'Waka waka!'";
close(STDOUT);
close(STDERR);
open(STDOUT, ">&SAVE1");
open(STDERR, ">&SAVE2");
open(INPUT, $TRAP) || die("$!: $TRAP");
$chldoutput = <INPUT>;
print "ABC: $chldoutput\n";
unlink($TRAP);
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-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=3333">st<
+/A>)/'\$1/mg"
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I s/OUPUT/INPUT/ while editing as I thought "OUTPUT opened only for output" sounded odd and I missed one.

-- 
perl -p -e "s/(?:\w);(<A HREF="/index.pl?node=st&lastnode_id=3333">st<
+/A>)/'\$1/mg"
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