[ale] FD 3 on gpg?

Neal Rhodes neal at mnopltd.com
Mon Nov 18 10:49:56 EST 2013


yes, indeed the wily script has this buried: 

    exec 3</home/<i-cant-tell-you>/k_file.asc

And this is apparently a one-shot trick;   Run that gpg command once,
and it has eaten the response.   run again, and there ain't no response
there no mo. 



On Mon, 2013-11-18 at 13:55 +0000, Lightner, Jeff wrote:
> File descriptors are just ways to keep track of open files.
> (Remember everything in Linux/UNIX is really a “file” just not
> necessarily a “regular file”.)
> 
>  
> 
> There’s a good discussion of ways to set and use FDs other than 0-2
> at:
> 
> http://www.tldp.org/LDP/abs/html/io-redirection.html
> 
>  
> 
> Additionally I notice the man page for gpg has other options to SET
> file descriptors.
> 
>  
> 
> You might look at the rest of the script (or whatever calls it) to see
> if it is setting a FD before it gets to the line below.
> 
>  
> 
> 
> 
> 
>  
> 
>  
> 
> 
> From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of
> Neal Rhodes
> Sent: Sunday, November 17, 2013 11:57 PM
> To: Atlanta Linux Enthusiasts
> Subject: [ale] FD 3 on gpg?
> 
> 
> 
>  
> 
> Here is a boiled down script buried in the bowels of a system which
> uploads data from pharmacies: 
> 
> CMD="gpg --homedir $HOME_DIR/.gnupg --batch --passphrase-fd 3
> --decrypt $HOLD 2> /tmp/gpg.err.$$ | /usr/local/bin/$PARSER  2>>
> $LOG_FILE"
> eval "$CMD"
> 
> 
> Which actually works.    I cannot fathom how.    The FM says it will
> read the passphrase from file descriptor 3.  Uh...Stdin, Stdout,
> Stderr,  There goes 0, 1, 2.    uh, that would be a file defined
> within gpg? 
> 
> Well, it sorta works.   If you wiggle it, or jiggle it, modify it
> various ways, it stops working and typically says "Bad passphrase". 
> 
> This:
> 
> CMD="cat something-something-icanttellyou/k_file.asc | gpg --homedir
> $HOME_DIR/.gnupg --batch --passphrase-fd 0 --decrypt $HOLD
> 2> /tmp/gpg.err.$$ | /usr/local/bin/$PARSER 2>> $LOG_FILE"
> eval "$CMD"
> 
> 
> Does work reliably under various combinations. 
> 
> Maybe there is some magic about FD 3 here, but I'm not finding it.
> Something about gpg-agent? 
> 
> Neal Rhodes
> MNOP Ltd 
> 
> 
> 
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