When I am in a terminal, and I type /bin/bash, that starts up another bash shell, right?
Is it possible to find out, via some command, whether the current bash shell has been started from another bash shell?
Also, what are the implications of starting a shell inside another? (or does it not matter)
A version that also works with shells other than bash is:
ps -p `ps h -p $$ -o ppid` -o comm=
Whit this command you can see the parent process of the current shell:
ps -o comm= -p $(echo $PPID)
This works in bash where PPID variable is defined, don't know in other shells.
EDIT
As @bmk noticed, the echo stuff is overkill and not necessary:
ps -o comm= -p $PPID
ps -o comm= -p $(echo $PPID) gives gnome-terminal. Running /bin/bash, and then ps -o comm= -p $(echo $PPID) gives bash.
echo for? I think it should also work without it: ps -o comm= -p $PPID
bash). Therefore: It works and it does what it should. It's just a bit overhead and doesn't work with different shells.
bash actually does count that via a special, exported variable SHLVL.
$ echo "$SHLVL"
1
$ bash -c 'echo "$SHLVL"'
2
If SHLVL is 2 though, it doesn't necessarily mean that the parent process is bash, it just means that one of the shell's ancestors is also bash, or another process that has exported SHLVL (ksh sets it too I think).
Why do you need to know if your shell's parent is bash?
And no, there's not really any implications of running a shell inside another shell. It's just like running any other command in a shell.
