如何使BASH脚本仅在特定目录中工作？

$PWD

~

if [[ "$PWD" == "/home/tareas/session_3" ]]; then
  # do stuff if true
else
  # do stuff if false
fi

#!/bin/sh

TARGET_DIR = "~/tareas/sesion_3" 

function do_something(){
    #do something
}

function do_something_v2(){
    #create some dirs
}

if [ `pwd` == "$TARGET_DIR" ] ; then
    do_something
else 
    do_something_v2

grep

echo `pwd` | grep ^/starting/directory >/dev/null || {
       echo "You aren't in the proper place .."
       exit 1
}

tpost@tpost-desktop:~$ echo `pwd` | grep ^/home/tpost >/dev/null || echo nope
tpost@tpost-desktop:~$ echo `pwd` | grep ^/home/foo >/dev/null || echo nope
nope

^