[ale] FD 3 on gpg?

[Lightner, Jeff]

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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