Shell 101 - $(), ${}, env, export

https://stackoverflow.com/questions/27472540/difference-between-and-in-bash

 $() means: "first evaluate this, and then evaluate the rest of the line".

Ex :

echo $(pwd)/myFile.txt

will be interpreted as

echo /my/path/myFile.txt

On the other hand ${} expands a variable.
Ex:
MY_VAR=toto
echo ${MY_VAR}/myFile.txt
will be interpreted as
echo toto/myFile.txt


$ is same as ${}

// https://www.linuxtechi.com/variables-in-shell-scripting/

print list of all ENV
printenv command 

print ENV variable :
echo $HOME

// 
export is to export vairable for sub process(if used on terminal, put in bash_profile for current user session)

https://stackoverflow.com/questions/7411455/what-does-export-do-in-shell-programming


$ foo=bar
$ bash -c 'echo $foo'

$ export foo
$ bash -c 'echo $foo'
bar