Command Line Basics

https://jtcoders.github.io/intro-to-command-line

What is a Shell?

A text-based command interpreter

The most common shell (and default on OS X) is BASH

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

For Windows, we could use PowerShell, but today, we'll use ConEmu

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 targets

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

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 "/".

Relative: Desktop/Photos/grumpycat.jpg

Absolute: /Users/paigecrum/Desktop/Photos/grumpycat.jpg

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.

Feel free to use this whenever things get too cluttered.

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)

Exercise 1

1. Change to your personal server folder
2. Create a jobtrain/practice directory path
3. Navigate into the jobtrain/practice directory
4. Create a CLI directory
5. View the contents of the CLI directory
6. Navigate up two directories
7. Use the pwd command to verify you are home
8. Remove the jobtrain/practice/CLI path

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)

Exercise 2

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

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

more

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

Exercise 3

1. In the cli directory, output the contents of file2.txt to the terminal
2. Add a sentenceto 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

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

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

Exercise 4

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

Free Resources

• Learn Command Line the Hard Way Tutorial


• Bash Cheat Sheet


• Customize your Command Prompt