How to check if script invoked from main shell

[Phil Sutter]

Hi,

On Fri, Jul 27, 2012 at 10:20:35AM +0200, Harald Becker wrote:
> As here are many shell script experts a not so Busybox related
> question, except I'm using Busybox ash and want to use only builtin
> applets:
> 
> I need to change behavior of shell script(s) if they get invoked from a
> main shell, that is a shell (interactive or not) which is a direct
> child of process #1 (init). How to determine if script has been invoked
> in this environment? What is the best/easiest solution for this?
> 
> An example to clarify my needs:
> 
> I have a shell invoked from init:
> 
> $ echo "pids=$$,$PPID"
> pids=156,1
> 
> And a multi function script command invoked by root in several
> situations:
> 
> File /root/bin/doit:
> 
> #!/bin/busybox sh
> echo "script pids=$$,$PPID"
> exit 0
> 
> $ doit
> script pids=1007,156
> 
> How does this doit script know if it is invoked from a top level shell
> in the shown sense or from any other shell (not direct child of init
> process)?

You could perhaps try to:
| grep -q '^PPid:[[:space:]]*1$' /proc/$PPID/status' \
| 	&& echo "parent is child of init" \
| 	|| echo "parent is no child of init"

HTH, Phil

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