Intro to the Command Line

teaching-materials.org/cli

Agenda

This class will be a combo of lecture + exercises

• Why use the command line?
• Command line "lingo"
• Working with folder directories
• Working with files
• Standard input/output
• Working with commands

When will I use this?

You might use the command line to...

• Automate file actions with a script
• Serve a local directory for testing
• Use version control (like Git)
• Run open source projects
• Use automated build tools
• Control other computers

The "lingo"

• "Terminal"
• "Command-line"
• "Command prompt"
• "Shell"
• "Console"
• "CLI"

These are all pretty much the same thing.

What is a Terminal?

A text-based command interpreter.

The most common shell is "bash".

For Mac OS or Linux, use the "Terminal" application.

For Windows, use Git Bash.
(Download here if you haven't installed yet.)

Prompt

Prompt

Usually shows your username and computer name.

Indicates that the terminal is ready for a command.

Cursor

Cursor

Indicates your current spot in the terminal.

Shows you where the stuff you type will go.

Your First Command

1. Type echo hello into your terminal.
2. Press the enter key.

The Current Directory

pwd

(Print Working Directory)

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

pwd

(Print Working Directory)

clear

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

This is good for removing previous output that is unnecessary to the task at hand.

Feel free to use this whenever things get too cluttered.

Directories

Also referred to as "folders".

A container for files or other directories.

Nested files and directories can be referenced using paths.

Directory Trees

The set of all folders, taken together, makes up your entire file system.

This system is organized into a kind of upside down tree.

Directory Trees

At the very top of the tree is the root folder.

Paths

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

There are two kinds of paths:

• Relative: Desktop/the_project/overview.txt
• Absolute: /Users/jane/Desktop/logo.png

cd

The cd command changes the current working directory.

It expects a file path as an "argument".

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

cd

Shortcuts

• Current Directory: .
• Parent Directory: ..
• Home Directory: ~
• Previous Directory: -

Bonus: Drag a folder into the terminal to show its path.

(Doesn't quite work in Windows.)

ls

The ls command lists the contents of a directory.

It expects a file path as an "argument".

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

ls

Flags

The ls command accepts several option flags.

A flag is a special argument that is used to set an option for the command.

These are commonly a hyphen followed by a single character (e.g. -g)

Setting the -l flag on the ls command causes it to provide more verbose (long) output.

ls -l

Hidden Files

Filenames that begin with a period are hidden from normal output.

e.g. ".bashrc"

Use the ls command with the -a flag to see hidden files in addition to the usual output.

Type ls -la into your terminal.

Use the -h flag to get human readable file sizes.

ls -la

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

cd & ls

Play with the cd and ls commands.

Be sure to incorporate:

• relative file path
• absolute file path
• the . shortcut
• the .. shortcut
• the ~ shortcut
• cd without an argument

Use pwd to check your location periodically.

Open

Use the open command to open a file or directory in its default app.

Pass the path of the file or directory name as the argument.

It does the equivalent of double-clicking the item.

(Sadly, this does not work in Windows. 😞)

Making a Directory

Use the mkdir command to create a new empty directory.

Pass the path of the directory name as the first argument.

If the base of the path doesn't already exist, the command will fail.

Use the -p flag to create the full path if non-existent.

mkdir

Removing Directories

Use the rmdir command to remove an empty directory.

Use rm -r to remove a non-empty directory.

rmdir

Let's Develop It!

1. cd to your home directory.
2. Create the girl/develop directory path.
3. Navigate into the girl/develop directory.
4. Create the it directory.
5. Navigate up two directories.
6. Use the pwd command to verify you are home.
7. Remove the girl/develop/it path.

Let's Develop It

Files

Use cat to output the contents of a file to the console.

Use more to step through the contents of a file one screen at a time.

Use less to step backwards or forwards.

Let's Develop It!

Explore the /usr/share/misc files using cat, more, and less

Can you find your birth month's stone and flower in the birthtoken file?

Let's Develop It!

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 origin destination

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 origin destination

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 origin destination

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)

Let's Develop It!

1. Create a folder called cli
2. Make that folder your current working directory
3. Create two files: file1.txt, file2.txt
4. Copy file1.txt and call the copy file3.txt
5. Create a directory called folder1
6. Move file1.txt into folder1
7. List the contents of folder1 without going into it
8. Rename file1.txt to myfile.txt
9. Remove the directory folder1, without deleting myfile.txt first
10. Clear your terminal

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)

Standard Output

Most commands display their results to a mechanism called the standard output.

By default, this directs its content to the display.

The standard output can be redirected to a file using the > operator.

ls > file_list.txt

Standard Output

In order to append to the file instead of overwriting it, use the >> operator instead.

ls >> file_list.txt

Both the > and >> operator will create the file if it doesn't exist.

Standard Input

Whenever commands accept keyboard input, it's likely they are really just drawing input from a mechanism called standard input.

By default, this is set to keyboard input.

Standard Input

The input to a command can be redirected to a file by using the < operator.

sort < file_list.txt

Both input and output can be redirected at the same time.

sort < file_list.txt > sorted_file_list.txt

Let's develop it!

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

Filters

Filters are commands whose behavior follows the following pattern:

1. Accept input from standard input.
2. Perform some operation on it.
3. Send the results to standard output.

Filters

Check out the man pages for the following:

Pipes

The "|" character can be used to allow commands to communicate during execution.

Pipes are placed between commands.

A pipe will cause the output of the left command to be used as the input of the right command.

ls -l | grep "myfile.txt" du | sort -nr

Let's Develop It!

Use the ls and grep commands to print out only the files in your home directory that contain the word "bash".

Let's Develop It!

ls -a | grep bash

Command Line Movement

• ctrl-a: jump to beginning of line
• ctrl-e: jump to end of line
• alt-f: jump forward a word
• alt-b: jump back a word
• alt-d: delete word
• alt-t: transpose two words
• ctrl-xx: jump back to your last edit, again to get back to original position

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

Bonus for Macs: Hold the option key and click to move the cursor.

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

Let's Develop It!

1. Use your up and down arrows to locate a past command with one or more arguments.
2. Move your cursor to the beginning of the line.
3. Move your cursor to the end of the line.
4. Change one of the arguments and run it.
5. Run the date command.
6. Re-run the command from step 4 using !.
7. Time the execution of your original command by running time !!.

Real World Examples

Let's revisit the use cases from the beginning of class and go into more detail.

Serve up a Directory

python -m simpleHTTPServer

Run this from the directory you want to serve.
Press Ctrl + C to exit.

Version Control

Check out Try Git for an intro, or watch for our next GDI Git workshop.

Run Open Source Projects

Installation instructions from an actual open source project:

Control other computers

These "other" computers might be:

• A cloud environment like Cloud9
• A virtual machine or container on your own computer
• A very simple computer like a raspberry pi

ssh gdi@192.168.0.23

Watching a Log File

tail -f /var/log/wifi.log

Troubleshooting: Where's the prompt?!

Different processes have different ways of exiting back to the prompt. If you're stuck, try one of these:

• ctrl + c
• ctrl + x
• q
• :q
• esc key, then :q

Troubleshooting:
`command not found`

You may need to install the software that uses the command.

Try searching online for:

Just for Fun!

cal

say hello

More Resources

• Command Line Cheat Sheet
• ConEmu: a cool customizable terminal emulator for Windows
• Nathaniel Landau: My Mac OSX Bash Profile
• tuts+: How to Customize the Command Prompt
• Terminal tricks on Stack Exchange