How do I know if a bash script is running with nohup?

Question

I have a script to process records in some files, it usually takes 1-2 hours. When it's running, it prints a progress of number of records processed.

Now, what I want to do is: when it's running with nohup, I don't want it to print the progress; it should print progress only when it run manually.

My question is how do I know if a bash script is running with nohup?

Suppose the command is nohup myscript.sh &. In the script, how do I get the nohup from command line? I tried to use $0, but it gives myscript.sh.

Answer 1

Checking for file redirections is not robust, since nohup can be (and often is) used in scripts where stdin, stdout and/or stderr are already explicitly redirected.

Aside from these redirections, the only thing nohup does is ignore the SIGHUP signal (thanks to Blrfl for the link.)

So, really what we're asking for is a way to detect if SIGHUP is being ignored. In linux, the signal ignore mask is exposed in /proc/$PID/status, in the least-significant bit of the SigIgn hex string.

Provided we know the pid of the bash script we want to check, we can use egrep. Here I see if the current shell is ignoring SIGHUP (i.e. is "nohuppy"):

$ egrep -q "SigIgn:\s.{15}[13579bdf]" /proc/$$/status && echo nohuppy || echo normal
normal
$ nohup bash -c 'egrep -q "SigIgn:\s.{15}[13579bdf]" /proc/$$/status && echo nohuppy || echo normal'; cat nohup.out
nohup: ignoring input and appending output to `nohup.out'
nohuppy

Answer 2

You could check if STDOUT is associated with a terminal:

[ -t 1 ]