Based upon your described requirements, the following code using the new_tmpfile method of IO::File may suffice:

use IO::File;

my $fh = IO::File->new_tmpfile;

.
.
.

$fh->seek(0, 0);
print STDOUT $_ foreach <$fh>;
$fh->close;
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This code creates a temporary file using the new_tmpfile method of IO::File - This method creates a temporary file, based on the POSIX tmpfile() function or tmpfile() from glibc if using Perl I/O abstraction, and then, where possible, unlinks the file while still holding it open. The result is an anonymous file handle suitable for the temporary storage of data - The data is stored in a stdio stream. The only disadvantage with this method of file name generation is that the temporary file cannot be referenced other than through the returned file handle.

The perlfunc:seek function is then used to move the current read/write pointer within the file back to the start of the file, allowing the process output to be re-read in full for reporting to STDOUT.

        #code from a sub
        unless (open(MAIL, "| $sendmail ")) {
                return 0
        };

        my $attach=$q->param('upfile');
        my $path = $q->tmpFileName($attach);
        open (ATTACH,"cat $path | mimencode |") or return 0;

        [cut]

        close ATTACH;
        close MAIL;
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~Particle *accelerates*