Command Line -- Lesson 3

In this lesson, I learned to use the bash profile to configure the environment.

The environment refers
to the preferences and settings of the current user.
The nano editor
is a command line text editor used to configure the environment.
~/.bash_profile is
where environment settings are stored. You can edit this file with nano.
environment variables are
variables that can be used across commands and programs and hold information about the environment.

export VARIABLE="Value"

sets
and exports an environment variable.

USER

is
the name of the current user.

PS1

is
the command prompt.

HOME

is
the home directory. It is usually not customized.

PATH

returns
a colon separated list of file paths. It is customized in advanced cases.

env

returns
a list of environment variables.

$ nano hello.txt[/code]

nano is
a command line text editor. It works just like a desktop text editor like TextEdit or Notepad, except that it is accessible from the command line and only accepts keyboard input.

The command

nano
hello.txt

opens a new text file named hello.txt in
the nano text editor.

"Hello, I am nano"

is
a text string entered in nano through the cursor.
The menu of keyboard commands at the bottom of the window allow us to save changes to hello.txt and
exit nano. The

^

stands
for the

Ctrl

key.

Ctrl

+

O

saves
a file. 'O' stands for output.

Ctrl

+

X

exits
the nano program. 'X' stands for exit.

Ctrl

+

G

opens
a help menu.

clear

clears
the terminal window, moving the command prompt to the top of the screen.

Please refer to
GNU nano for detailed information.

$ nano ~/.bash_profile[/code]

~/.bash_profile is
the name of file used to store environment settings. It is commonly called the "bash profile". When a session starts, it will load the contents of the bash profile before
executing commands.

The

~

represents
the user's home directory.
The

.

indicates
a hidden file.
The name ~/.bash_profile is
important, since this is how the command line recognizes the bash profile.

The command

nano
~/.bash_profile

opens up ~/.bash_profile in
nano.
The text

echo
"Welcome, Jane Doe"

creates a greeting in the bash profile, which is saved. It tells the command line to

echo

the
string "Welcome, Jane Doe" when a terminal session begins.
The command

source
~/.bash_profile

activates the changes[/u]
in ~/.bash_profile for
the current session. Instead of closing the terminal and needing to start a new session,

source

makes
the changes available right away in the session we are in.

alias pd="pwd"[/code]

The

alias

command
allows you to create keyboard shortcuts, or aliases, for commonly used commands.

Here

alias
pd="pwd"

creates the alias

pd

for
the

pwd

command,
which is then saved in the bash profile. Each time you enter

pd

,
the output will be the same as the

pwd

command.
The command

source
~/.bash_profile

makes the alias

pd

available
in the current session.

alias hy="history"[/code]

hy

is
set as alias for the

history

command
in the bash profile. The alias is then made available in the current session through

source

.
By typing

hy

, the command
line outputs a history of commands that were entered in the current session.

alias ll="ls -la"[/code]

ll

is
set as an alias for

ls -la

and
made available in the current session through

source

.
By typing

ll

, the command
line now outputs all contents and directories in long format, including all hidden files.

export USER="Jane Doe"[/code]

environment variables are
variables that can be used across commands and programs and hold information about the environment.

The line

USER="Jane
Doe"

sets the environment variable USER to a name "Jane Doe". Usually the USER variable is set to the name of the computer's owner.
The line

export

makes
the variable to be available to all child sessions initiated from the session you are in. This is a way to make the variable persist across programs.
At the command line, the command

echo
$USER

returns the value of the variable. Note that

$

is
always used when returning a variable's value. Here, the command

echo
$USER

returns the name set for the variable.

export PS1=">> "[/code]

PS1

is
a variable that defines the makeup and style of the command prompt.

export PS1=">> "

sets
the command prompt variable and exports the variable. Here we change the default command prompt from

$

to

>>

.
After using the

source

command,
the command line displays the new command prompt.

$ echo $HOME[/code]

The

HOME

variable
is an environment variable that displays the path of the home directory. Here by typing

echo
$HOME

, the terminal displays the path/home/ccuser as
output.

$ echo $PATH

/home/ccuser/.gem/ruby/2.0.0/bin:/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/sbin:/sbin:/bin[/code]

PATH

is
an environment variable that stores a list of directories separated by a colon. Looking carefully,

echo
$PATH

lists the following directories:

/home/ccuser/.gem/ruby/2.0.0/bin
/usr/local/sbin
/usr/local/bin
/usr/bin
/usr/sbin
/sbin
/bin

Each directory contains scripts for the command line to execute. The

PATH

variable
simply lists which directories contain scripts.

For example, many commands we've learned are scripts stored in the /bindirectory.

/bin/pwd[/code]

This is the script that is executed when you type the

pwd

command.

/bin/ls[/code]

This is the script that is executed when you type the

ls

command.

env[/code]

The

env

command
stands for "environment", and returns a list of the environment variables for the current user. Here, the

env

command
returns a number of variables, including

PATH

,

PWD

,

PS1

,
and

HOME

.

env | grep PATH[/code]

env
| grep PATH

is a command that displays the value of a single environment variable. Here the standard output of

env

is
"piped" to the

grep

command.

grep

searches
for the value of the variable

PATH

and
outputs it to the terminal.