pwd: print working directory
hostname: my computer's network name
mkdir: make directory
cd: change directory (~:home, /:root, ..:up, ../../directory: 2up and go another directory)
ls: list directory (l:details, p:shows files with/, a:hidden included)
rmdir: remove directory
pushd: push directory
popd: pop directory
cp: copy a file or directory [source][destination]
mv: move, rename a file or directory
less: page through a file
cat: print the whole file (short for "concatenate")(cat FILE > FILE to copy)
xargs: execute arguments
find: find files
grep: searches for lines which contain a search pattern
man: read a manual page
apropos: find what man page is appropriate
env: look at your environment
echo: print some arguments
export: export/set a new environment variable
exit: exit the shell
sudo: super user do!
chmod: change permission modifiers
chown: change ownership
diff: shows the differences between
groups: shows which groups a user is a member of.
ping: checks connectivity status to a server
wget: download files from the internet 
date: show date and time
cal: show calendar
!17 run 17th command on history