The C standard says that the file streams stdin
, stdout
, and stderr
shall be connected somewhere, but they don't specify where, of course.
(C11 §7.21.3 Files ¶7:
At program startup, three text streams are predefined and need not be opened explicitly -- standard input (for reading conventional input), standard output (for writing conventional output), and standard error (for writing diagnostic output). As initially opened, the standard error stream is not fully buffered; the standard input and standard output streams are fully buffered if and only if the stream can be determined not to refer to an interactive device.
It is perfectly feasible to run a program with the standard streams redirected:
some_program_of_yours >/dev/null 2>&1 </dev/null
Your writes will succeed - but the information won't go anywhere. A more brutal way of running your program is:
some_program_of_yours >&- 2>&- </dev/null
This time, it has been run without open file streams for stdout
and stderr
— in contravention of the the standard. It is still reading from /dev/null
in the example, which means it doesn't get any useful data input from stdin
.
Many a program doesn't bother to check that the standard I/O channels are open. Many a program doesn't bother to check that the error message was successfully written. Devising a suitable fallback as outline by Tim Post and whitey04 isn't always worth the effort. If you run the ls
command with its outputs suppressed, it will simply do what it can and exits with a non-zero status:
$ ls; echo $?
gls
0
$ ls >&- 2>&-; echo $?
2
$
(Tested RHEL Linux.) There really isn't a need for it to do more. On the other hand, if your program is supposed to run in the background and write to a log file, it probably won't write much to stderr
, unless it fails to open the log file (or spots an error on the log file).
Note that if you fall back on syslog(3)
(or POSIX), you have no way of knowing whether your calls were 'successful' or not; the syslog
functions all return no status information. You just have to assume that they were successful. It is your last resort, therefore.