Ick.

Untested: 

use IO::Scalar;
my $data;
tie *HACK, 'IO::Scalar', \$data;
print HACK <STDIN>;
tied(*HACK)->setpos(0);
*STDIN = *HACK;

[download]
Now if you don't destroy anything, reading from STDIN gives you what is already in $data which is what was in STDIN.

UPDATE
The idea was good but apparently copying tied stuff like that does not maintain the tie. (I shoulda known that, sorry.) Try this code instead: 

use IO::Scalar;
$data = join '', <STDIN>;
my $s;
tie *STDIN, 'IO::Scalar', \$s;
print STDIN $data;
tied(*STDIN)->setpos(0);

[download]
I tested this by adding 
print $data;
print <STDIN>;

[download]
after it, running it, and typing into it.

My apologies for the initial mistake.

In reply to Re (tilly) 1: How to preserve the value of STDIN by tilly
in thread How to preserve the value of STDIN by Ovid

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