File-descriptors: redirection wanted

romagnolo · 03-17-2011, 03:54 PM

I need to redirect the process A's standard output to B's standard input.
Problem is A and B aren't directly related and can't be written down on the same pipeline of bash script (A | B).

Looking for solutions, I read about those file descriptors in /proc/<pid>/fd/ which promise to pipe directly into the process interface, but I did't get too much far.
If I push text trough any of them, that text apperas on the receiving process' console, but isn't interpreted, like if it was passed as output instead of as input.

In my concrete machine, B, the receiving process, is gimp-console, and A, the output-generator, is a generic script; other combinations of processes behaved the same way.

I noticed that file-descriptors 0 1 2 point to the same special-file; don't know if that's sane:

Code:

$ ls -l /proc/`pidof gimp-console`/fd/
total 0
lrwx------ 1 davide davide 64 Mar 17 20:48 0 -> /dev/pts/0
lrwx------ 1 davide davide 64 Mar 17 20:48 1 -> /dev/pts/0
l-wx------ 1 davide davide 64 Mar 17 20:48 10 -> pipe:[261933]
lrwx------ 1 davide davide 64 Mar 17 20:48 2 -> /dev/pts/0
lr-x------ 1 davide davide 64 Mar 17 20:48 3 -> pipe:[261925]
lr-x------ 1 davide davide 64 Mar 17 20:48 4 -> pipe:[261929]
l-wx------ 1 davide davide 64 Mar 17 20:48 5 -> pipe:[261929]
l-wx------ 1 davide davide 64 Mar 17 20:48 6 -> pipe:[261926]
lr-x------ 1 davide davide 64 Mar 17 20:48 7 -> pipe:[261932]

kbp · 03-17-2011, 10:51 PM

Unless the application is expecting input from stdin I don't think what you're doing is going to work... happy to be corrected though. Descriptors 0,1 and 2 should map to stdin, stdout and stderr if that helps

cheers

romagnolo · 03-18-2011, 08:23 AM

Obviously it does. Anyway, I could change my problem avoiding those links in /proc/<pid>/fd/ , relying on a regular bash pipe. Problem becomes: pipe must never break.
Gimp-console beheaves in two totally different ways whether it detects a pipe or not.
In the former case, gimp terminates as soon as stream ends; in the latter, it waits.
I have a raw workaround to keep the pipe opened, and so gimp: flood the stream with ininfluent data when nothin has to pass trough. For example by the means of:
$ yes some-ininfluent-data
with high nice value.

If you have better solutions in mind, please let me know. thanks.