Bash script with different CWD from parent shell?

I'm doing a puzzle for my computer science class where I need to execute the binary /challenge/executable via a shell script, from the CWD of /tmp/exampledir, with the shell's CWD being a different directory from the shell script's, or as the challenge phrases it:

• the challenge checks for a specific parent process : shellscript
• the challenge will check that it is running in a specific current working directory : /tmp/exampledir
• the challenge will check to make sure that the parent's parent CWD to be different than the challenge's CWD

My interpretation of what I'm supposed to do was run a shell script, stored in /tmp/exampledir, from a different directory, but the cwd of the bash script changed to where I ran it from. I tried putting cd /tmp/exampledir into the bash script and running it from another directory, but when I ran it, it said that both the shell script and the parent process were in the CWD of /tmp/exampledir. Is there something I'm missing here? Thanks!

Since the current working directory is inherited from the parent process, you need something that will change the directory and then replace itself with the desired command. For that, this should work:

sh -c 'cd /tmp/exampledir; exec /challenge/executable'

The key part being exec, which replaces the shell process with the specified command.

For example, this script should behave like the challenge executable:

#! /bin/bash

printf "My PWD is %q. The PWD of my parent process is %q.\n" "$PWD" "$(readlink /proc/$PPID/cwd)"

And then:

# ./foo.sh
My PWD is /home/muru. The PWD of my parent process is /home/muru.
# sh -c 'cd /tmp; exec /home/muru/foo.sh'
My PWD is /tmp. The PWD of my parent process is /home/muru.
# mkdir -p "foo bar"
# cd "foo bar"
# sh -c 'cd /tmp; exec /home/muru/foo.sh'
My PWD is /tmp. The PWD of my parent process is /home/muru/foo\ bar.