What is a Shell?

An interface provided to the user, so he/she can interact with the OS core services (kernel)

Can be a CLI

(Command-Line Interface)...

Shell == Terminal?

Terminal

Shell

reads commands

prints results

Back in Ol' 70s

Terminal

Shell

reads commands

prints results

Now

Shell Implementations

• sh (Bourne Shell)
• ksh (Korn Shell)
• csh (C Shell)
• tcsh
• Bash (Bourne Again Shell)
• zsh
• fish (Friendly Interactive Shell)
• etc., etc., etc.

Shell Types

Login

• Started after a system login. (1)
• Sources the following files (2):

  • /etc/profile

  • ~/.bash_profile OR ~/.bash_login OR ~/.profile (3)

• Allows finishing the shell with the logout command.
• On logout, sources ~/.bash_logout.

1. A login shell can be started interactively with bash --login.
2. Bash-specific.
3. Searches files in that order and sources the first one it finds, ignoring the rest.

vs.

Non-Login

• Started by the user or as a sub-shell.
• Only sources ~/.bashrc. (2)
• Uses the exit command to finish the shell.

Interactive

vs.

Non-Interactive

Basic Commands

echo

~ $ echo 'Hello world!'
Hello world!


~ $ echo 'Hello\nworld!'
Hello\nworld!


~ $ echo -e 'Hello\nworld!'
Hello
world!


~ $ echo '$HOME'
$HOME


~ $ echo "$HOME"
/home/santiaro90

cat

# Don't worry about what '>' means, for the moment...
~ $ echo -e 'Hello\nworld!' > hello.txt
~ $ echo 'Hola Mundo' > hola.txt


~ $ cat hello.txt
Hello
world!


~ $ cat hello.txt hola.txt
Hello
world!
Hola Mundo


~ $ cat -n hello.txt
    1. Hello
    2. world!

cd (Change Directory)

# Go to ~/Documents/Important...
~ $ cd ~/Documents/Important
~/Documents/Important $


# Go to $HOME (same as ~)
~/Documents/Important $ cd
~ $


# Take us back to the last directory we were in
~ $ cd -
~/Documents/Important $


# We can use relative paths :)
~/Documents/Important $ cd ./.././Important/../../Downloads
~/Downloads $

alias

~ $ alias web-projects='cd /home/santiaro90/Projects/Web; echo "Have a nice coding!"'
~ $ web-projects
Have a nice coding!
~/Projects/Web $


~ $ unalias web-projects
~ $ web-projects
-bash: web-projects: command not found

Other commands

# See documentation for a given command
~ $ man <command>


# Print current directory
~ $ pwd
/home/santiaro90


# See information for current user
~ $ who am i -H
NAME        LINE    TIME                COMMENT
santiaro90  pts/0   2016-08-25 11:35


# See information for all logged in users
~ $ who -H
NAME        LINE    TIME                COMMENT
santiaro90  pts/0   2016-08-25 11:35    (192.168.56.1)
root        tty2    2016-08-25 11:28
santiaro90  :0      2016-08-25 12:10


# Print current date
~ $ date
Sun 28 Aug 18:58:28 COT 2016