variable=42
bash -c 'echo $variable'
export variable
bash -c 'echo $variable'

echo 'export variable1=23' >> /etc/profile
echo 'export variable2=23' >> ~/.bashrc

echo 'export variable3=23' >> ~/.bash_profile

export variable=23
env | grep ^variable

• http://tldp.org/LDP/abs/html/variables.html
• http://tldp.org/LDP/abs/html/variables2.html