1. Assign a string to a variable is the same as other language by using "=".
2. Use $ sign to access a variable.
echo $FOOD
3. Use export to create a environmental variable.
4. type python to enter the python shell. Use exit() to exit.
5. use $PATH to enter variable PATH.
6. Flags like the arguments of fucntion. us - to use flags.
ls -al #shows flag a and flag l
7. Longer flags like ingore need to use two dashes.
ls --ignore=test.txt # we won‘t show the file named test.txt
原文：http://www.cnblogs.com/kingoscar/p/6021601.html