In /proc, there are subdirectories for each process running on the system, having name based on the PID number of the process. In each of these directories, there is a fd/ subdirectory that contains files that represent the file descriptors the process currently has open. These files are actually symlinks that point to the actual device, socket, or other file the process currently has open and mapped to that file descriptor. If you have a program that can read input from a file but not from standard input, or that can write to a file but not to standard output, you may be able to cheat by taking advantage of these special files:
/proc/self/fd/0 is standard input of the current process
/proc/self/fd/1 is standard output of the current process
/proc/self/fd/2 is standard error of the current process
Linux, Programming, Bash & my thoughts…
