processes | environment variables

The shell is an interpreter that executes commands on the user's behalf
The terminal is not the same as the shell
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Check which shell is running:
ubuntu@ubuntu:~$ echo $0
bash
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pipe |  allows using the output from some commands as an input to other

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ubuntu@ubuntu:~$ vim &
[1] 4515
ubuntu@ubuntu:~$ ps
  PID TTY          TIME CMD
 3255 pts/0    00:00:00 bash
 4515 pts/0    00:00:00 vim
 4522 pts/0    00:00:00 ps

[1]+  Stopped                 vim
ubuntu@ubuntu:~$ jobs
[1]+  Stopped                 vim
ubuntu@ubuntu:~$ fg %1
vim           #runs VIM
ubuntu@ubuntu:~$

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ubuntu@ubuntu:~$ pwd_text=$(pwd;date)

ubuntu@ubuntu:~$ echo "pwd_text"

pwd_text

ubuntu@ubuntu:~$ echo "$pwd_text"

/home/ubuntu

Sun Mar 15 02:58:32 PDT 2015

ubuntu@ubuntu:~$ 

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to make variable - environment variable

ubuntu@ubuntu:~$ export pwd_text=$(pwd;date)

to remove a variable

ubuntu@ubuntu:~$ unset pwd_text

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environment variables are available for all processes on the system

printenv displays all environment variables 

ubuntu@ubuntu:~$ printenv | grep -i shell

SHELL=/bin/bash

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