How to preserve the value of STDIN

Ovid has asked for the wisdom of the Perl Monks concerning the following question:

Here's the problem. I'm the new guy at a company and walked into discover that, amongst other things, they don't use CGI.pm for CGI scripts. They have a rather limited in-house script that is insufficient for our needs. I need to allow users to upload files images to our server, but their script won't handle it, so I need to use CGI.pm. However, for various reasons, we need to call their script first because it does a lot of funky stuff with the data that fits their in-house work. Naturally, since their script clobbers STDIN, CGI.pm can't get to the data on a post (which is what I need when I use multipart/form-data).

So the question is, how do I preserve what's in STDIN so CGI.pm can read it? Here's Fastolfe's suggestion:

local($/); 
$data = <STDIN>; 
my $A = IO::String->new ($data);
my $B = IO::String->new ($data);
[download]

Later, CGI.pm would be called like the following:

use CGI ($B);
[download]

Any comments/suggestions? The IS manager agrees that we need to convert everything to CGI.pm, however, we probably have about 15,000 lines of code to go through and we can't do this before the site roll-out :( In short, I need to get a quick, ugly hack together and then fix this later.

Cheers,
Ovid

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Comment on How to preserve the value of STDIN Select or Download Code

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Re (tilly) 1: How to preserve the value of STDIN by tilly (Archbishop) on Sep 22, 2000 at 03:22 UTC
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 $data; print <STDIN>;` [download] after it, running it, and typing into it. My apologies for the initial mistake.	[reply] [d/l] [select]
(Ovid) RE: Re (tilly) 1: How to preserve the value of STDIN by Ovid (Cardinal) on Sep 22, 2000 at 03:58 UTC
I love you. ;) Join the Perlmonks Setiathome Group or just go the the link and check out our stats.	[reply]
Re^2: Re (tilly) 1: How to preserve the value of STDIN by Anonymous Monk on Feb 07, 2013 at 19:06 UTC
I don't understand why it works, this is pure magic	[reply]
Re: How to preserve the value of STDIN by chromatic (Archbishop) on Sep 22, 2000 at 03:08 UTC
If you can copy STDIN before anything reads from it, you might have luck. The following code works for me under Linux: `#!/usr/bin/perl -w use strict; open (NEWIN, "<&STDIN") or die "$!"; open (STDIN, "/dev/null"); print while (<NEWIN>);` [download] I saved it as 'dup.pl' and called it with `cat dup.pl \| ./dup.pl`. (Find out about <& at open.) Of course, you can pass a reference to a typeglob containing the NEWIN fh to the CGI.pm constructor...	[reply] [d/l] [select]
RE: Re: How to preserve the value of STDIN by Fastolfe (Vicar) on Sep 22, 2000 at 03:10 UTC
This is still only a one-shot deal. `<STDIN>` now immediately returns an EOF (since we're reading from /dev/null now) as will any subsequent read from `<NEWIN>` (since we've read everything from what was once STDIN). We're not gaining anything here, in other words. He needs his in-house stuff to parse STDIN as well as CGI.pm. Both of them are written to read from STDIN, and only the first will succeed. If this were a normal file handle, we could `seek(STDIN, 0, 0)` to return it to a sane, starting state, but you can't do this with STDIN, because it's actually more like a pipe than a file.	[reply] [d/l] [select]
Re: How to preserve the value of STDIN by Fastolfe (Vicar) on Sep 22, 2000 at 03:08 UTC
Note that this would still destroy STDIN, but at least you have the data available to the two parts of your application that need it. They just need to be re-written to use `<$A>` and/or `<$B>` instead of `<STDIN>`. You could actually even do without the 2nd variable: `my $A = new IO::String ($data); &exhaust_file_handle($A); # read everything from $A $A->setpos(0); # rewind &also_exhaust($A); # 2nd process reads everything from $A` [download] Since `$A` isn't a native file handle, you can't seek() on it, but this will do just as well and should be indistinguishable from your two separate processes. You will also need to do this in a `BEGIN { }` block, so that all of this mangling of `STDIN` is done before `use CGI ($A)` is called.	[reply] [d/l] [select]