Can a shell script set environment variables of the calling shell? [duplicate]

Answer 1

Under OS X bash you can do the following:
Create the bash script file to unset the variable

#!/bin/bash
unset http_proxy

Make the file executable

sudo chmod 744 unsetvar

Create alias

alias unsetvar='source /your/path/to/the/script/unsetvar'

It should be ready to use so long you have the folder containing your script file appended to the path.