Introduction to the Command Line

Welcome!

Girl Develop It is here to provide affordable and accessible programs to learn software through mentorship and hands-on instruction.

Some "rules":

We are here for you!
Every question is important
Help each other out
Have fun

Meet Your Instructor

Maureen McElaney

@mo_mack

Now it's all about you!

Tell us who you are.
What do you hope to get out of this class?

What we'll be covering in this class

Navigating and searching through files and directories
Input/Output Redirection
Installing Programs
Changing file permissions and file ownership

What is a Shell?

A text-based command interpreter

The most common shell is called BASH

For OS X, use a shell via the “Terminal” app

The Shell

The Prompt

Usually shows your username and computer name (hostname).

It indicates that the shell is ready for you to enter a command.

Prompt

Command Structure

$ command -options argument

Don’t forget to hit enter at the end of each command.

Your First Command

`echo`

Type echo hello to print hello to the screen

Man Pages

`man`

The man command brings up the manual for the specified command. Use <space> or the arrow keys to page through and press q to exit.

$ man ls

Love the Tab

Tab completion autocompletes commands and filenames.

Pressing <tab> once autocompletes a unique instance.
Pressing <tab> twice gives you all the options available.

$ cd P

The Current Directory

`pwd`

(Print Working Directory)

Type it whenever you want to see what directory (folder) you’re in.

pwd

(print working directory)

Directories

Containers for files or other directories.

Also referred to as "folders".

Nested files and directories can be referenced using paths.

File Paths

A sequence of nested directories, with a file or directory at the end.

Each directory or file is separated by a forward slash "/".

Two Types of Paths

Relative:
Desktop/dougthepug.jpg

Absolute:
/Users/anastasialanz/Desktop/dougthepug.jpg

Unix File Structure

In OS X, /home/you becomes /Users/you

File System Structure

Varies between systems, but some common folders:

/bin: Basic commands
/etc: System config files
/tmp: Temporary files
/usr: Regular user tools
/usr/local: Installed user software
/var: Data used by system

Shortcuts

Current Directory: (.)
Parent Directory: (..)
Home Directory: (~)
Root Directory: (/)

Change Directory

`cd`

Use the cd command to change directories.

Expects a file path as an argument.

If no file path is given, it assumes your home directory (~) by default.

cd

(change directory)

There are 2 other ways that we could have gotten to our home directory...what are they?

Clear your Terminal

`clear`

The clear command clears the contents of the terminal and issues a prompt.

$ clear

Option + L will also clear the terminal.

List Directory

`ls`

Use the ls command to list the contents of a directory.

Expects a file path as an argument.

If no file path is given, it assumes the current directory by default.

ls

(list directory)

Flags

Some commands have additional options that you can specify by using flags.

Flags are preceded by a hyphen, and are often a single character.

$ ls -a

$ ls -l

ls -a

-a = show hidden files

Notice that hidden file names begin with a "."

ls -l

-l = use a “long list” format (shows more verbose output)

ls -al

Show hidden files and use a long list format

You can combine flags or list them separately separated by spaces. (e.g. “ls -a -l”)

File Names

case sensitive
any character (besides “/”)
file extensions are for user convenience

Examples:

README   .bashrc   index.html    index.html.old    Bugs List.txt

Making and Removing Directories

Use the mkdir command to create a new empty directory.

Use the rmdir command to remove an empty directory.

Use rm -r to remove a non-empty directory
...be careful!

All 3 commands expect the name of a directory as an argument.

mkdir, rmdir

(make directory, remove directory)

Develop it!

Exercise 1

Change to your home directory desktop
Create a gdi/burlington directory path
Navigate into the gdi/burlington directory
Create a CLI directory
View the contents of the CLI directory
Navigate up two directories
Use the pwd command to verify you are home

Create a File

`touch`

Use the touch command to create a new file.

The touch command expects the name of your new file as an argument.

touch

(create a file)

Copy a File

`cp`

Use the cp command to copy a file.

The cp command takes two arguments:

1st argument = the "origin" file

2nd argument = the "destination" file

$ cp resume.txt resume-copy.txt

cp

(copy a file)

`$ cp orig dest`

Copy a Directory

`cp -R`

Use the cp -R command to copy a directory.

The cp -R command takes two arguments:

1st argument = the "origin" directory

2nd argument = the "destination" directory

$ cp -R homework old-homework

cp -R

(copy a directory)

`$ cp -R orig dest`

Moving (or renaming) a File/Directory

Use the mv command to move a file or directory.

The mv command takes two arguments:

1st argument = the "origin"

2nd argument = the "destination"

Move a File/Directory

`mv orig dest`

Rename a File/Directory

`mv orig dest`

Remove a File

`rm`

Use the rm command to remove a file.

Expects the name of the file you are removing as an argument.

rm

(remove a file)

Develop it!

Exercise 2

Create a folder called gdi
Make that folder your current working directory
Create two files: file1.txt, file2.txt
Copy file1.txt and call the copy file3.txt
Create a directory called folder1
Move file1.txt into folder1
List the contents of folder1 without going into it
Rename file1.txt to myfile.txt
Clear your terminal

View a File

`cat, more, less`

Use the cat command to output (catenate) the contents of a file to the console.

Use the more or less commands to read a file:

more allows you to step through the contents of a file a screen at a time
less allows you to step backwards or forwards

Press q to exit out of this mode

cat

(catenate)

will output the entire file

less

Edit a File

You can use various editors built into bash:

$ vi myfile.txt

$ emacs myfile.txt

$ pico myfile.txt

Or on a Mac, you can open with any desktop app:

$ open -a TextEdit myfile.txt

Or with the default editor:

$ open -t myfile.txt

Search within a File

`grep`

Use the grep command to search in files.

The grep command outputs only the lines in a file that match a given pattern.

The 1st argument is the pattern to match, and the 2nd, 3rd, and so on are the files to search within.

$ grep pattern file

grep

(search within a file for text that matches a pattern)

Wildcard Matching

Use the * (asterisk) symbol to match anything.

You can use this to search through all of a particular file type.

$ grep hello *.txt

The shell will build a list of all the files that match the non-asterisk part.

Finding Files

`find`

Use the find command to find files according to name/metadata.

Find all txt files under the current directory:

find . -name '*.txt' -print

find

(finding files)

Redirecting Output

By default, input comes from the screen and output goes to the screen.

You can use < and > to redirect input/output.

A practical example: Save results of search in a file:

grep hello *.txt > results.txt

Redirecting Output

Redirecting Output

Use the echo command to add a new line of text.

Use the > to replace the contents of a file.

Use the >> to add to the end of a file.

Redirecting Output

Develop it!

Exercise 3

In the gdi directory, output the contents of file2.txt to the terminal
Add a sentence to file2.txt
Add a few more sentences to file2.txt
Search the file for the word of your choice and add the results to file3.txt

Command Line Movement

ctrl-a: jump to beginning of line
ctrl-e: jump to end of line
ctrl-u: clear the line
ctrl-l: shortcode for clear
ctrl-r: search previous commands
ctrl-c: get out of trouble
ctrl-d: exit terminal

More Command Line Movement

The left/right arrow keys let you edit within a command
The up/down arrow keys let you select previous commands
tab auto-completes filenames

Lots more, and you can create your own.

Command Line History

Use the history command to see a list of all your previous commands.

Each command will be listed next to a line number.

A few history-related commands:

!!: Latest command
!568: Command by line #
!open: Command matching string

history

Develop it!

Exercise 4

Use your up and down arrows to locate a past command with one or more arguments
Jump to the beginning of the line
Jump to the end of the line
Look at your command line history
Begin to type a previous command and experiment with using tab to complete it

curl

A command line tool for getting or sending files using URL syntax.

$ which curl

Download a file with curl

The command below will download a .txt file

$ curl -OL example.com/pugs.txt

head

Shows the first 10 lines of a file.

tail

Shows the last 10 lines of a file.

wc

(Word count)

This command shows newline count, word count and byte count.

Pipe

The output of one command is the input of another command.

$ head cat.txt | wc

Use this command to chain multiple commands together.

Develop it!

Exercise 5

Download the cat.txt file by running this command:

$ curl -OL gdibtv.github.io/intro-to-command-line/cat.txt

Use the head command to see the first 10 lines of text.
Use the tail command to see the last 10 lines of text.
Pipe the results of grep cat cat.txt command through wc to count the number of times "cat" appears.
Using the grep man page, find the option for case insensitive matching. Try to find how many times "cat" and "Cat" appear.

Installing Programs

Use Homebrew for MacOs.

Use apt-get for Ubuntu.

cowsay

A program that generates ASCII pictures of cows with a message.

$ brew install cowsay

Extras

Open a URL in the browser with command line

$ open http://girldevelopit.com

Extras

Make your computer talk from the command line

$ say i love the command line

Develop it!

Install cowsay on your environment.
Use the cowsay man page to list the different cowfiles.
Generate 5 different cowsay cowfiles pictures using the - f option.
Open a url of your choice from the command line.
Use the man pages and find a different voice output for the say command.