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A beginners guide to the the unix-style command line

Filed under: System— Tagged with: shell, mysql

This posts looks into using computer from the command line: how to navigate around your file system and how to do basic tasks such as; creating/deleting folders and files, installing packages with apt-get, general terminology, customizing the terminal, and some more.

2014.04.11 Edit: Added some MySQL commands

2014.04.16 Edit: how to change password

Take off the...

It’s one of the things that seem hard, but actually are not (I mean the basics aren’t difficult), learn few commands and tricks and you’ll find it to be much better way of using a computer.

Terminology

Command Line Interface CLI — an umbrella term:

... is a means of interacting with a computer program where the user (or client) issues commands to the program in the form of successive lines of text (command lines).

Shell — the program you’re using:

The most generic sense of the term shell means any program that users employ to type commands.

Bash — a type of shell:

Bash is a Unix shell [...] a free software replacement for the Bourne shell [...] it has been distributed widely as the shell for the GNU operating system and as a default shell on Linux and Mac OS X.

Terminal — OS X shell:

Terminal (Terminal.app) is the terminal emulator included in the OS X operating system by Apple Inc..

Why would I want to learn that?

  1. There is a whole cosmos of GUI-less handy applications, you have more stuff at your disposal. For me one of the triggers was to be able to use Grunt
  2. Linux and OS X use a lot of the same commands, learn one and you know the other
  3. Servers are mostly Linux, learn to configure it from command line and you can run your own server. Configuring a server is the most ideal way to get comfortable with shell *

OS X Terminal

Terminal is in the Utilities folder inside Applications. Here's the default look.

Screenshot of the default OS X terminal application
Very basic OS X terminal as it comes out the box

Make it prettier and better

I recommend iTerm, it has tabs and bunch of other cool stuff. Some people also prefer TotalTerminal.

The default look is a bit morose, it can be made more interesting easily. Grab the .bash_prompt file from here and just drop it into your home directory, boot iTerm. You can customise the iTerm colours in it's Setting → Profiles → Colors (⌘ + ,), change the background to your preference. I like to have my text editor white and terminal black, so I can distinguish them easily.

Screenshot of iTerm 2
iTerm with a custom .bash_profile

You go to a directory with the cd command.

$ cd foldername

Really important thing is to use tab completion.

A gif showing tab completion on iTerm terminal
Tab completion

The above gif explained:

$ cd w<tab>

# Complets into
$ cd web/

# Next dir
$ cd web/be<tab>

# Completes into
$ cd web/beveled-corners

Start by typing few letters of the folder name and then press tab, and it’ll fill the whole name in for you. This is priceless!

If there is more folders with almost the same name (i.e. config.php and config-sample.php), it wont work of course, then you can double tab to see all the files with the same beginning.

Set of commonly used command

This section is just a dump of commands basically.

With these you can get pretty far already. The commands work both in Mac and Linux (unless otherwise mentioned).

Nomenclatures:

  • $ character means that it’s a line to be written in command prompt (don’t actually type the dollar character).
  • # is a comment.
  • If the line starts with nothing, it means it’s an output of a command.

Go to a folder:

$ cd foldername

List files:

$ ls

List also hidden files:

$ ls -a

List as a "list" and show the file sizes in human readable form:

$ ls -lah

Navigate to a different hard drive, usually only needed on a local computer:

$ cd /Volumes/"Some Volume Name Here"

The possible spaces in the directory names can also be escaped with a backslashes:

$ cd /Volumes/Some\ Volume\ Name\ Here

Where are you (pwd: Print Working Directory):

$ pwd
/path/to/your/current/location

Making

Make a folder (mkdir: MaKe Directory):

$ mkdir foldername

Make a blank new file:

$ touch some-file.txt

Make a file with content:

$ "your content" > foo.txt

Or based onto another file:

$ cat other-file.txt > foo.txt

Downloading/Uploading

Download a file from internet (wget: World Wide Web Get):

$ wget http://www.example.com/path/to/file.txt

Upload file to a server securely (scp: Secure Copy):

$ scp ./my-file.zip bob@127.0.0.0:/var/www/my-site

Download file from a server securely (to your current working directory):

$ scp bob@127.0.0.0:/var/www/my-site/my-file.zip ./

Get headers of a website:

$ curl -I "https://clubmate.fi"

Quickly check if an URL redirects:

$ curl -I -s "http://clubmate.fi" | grep Location:
Location: https://clubmate.fi/

The -s stands for "silent".

Opening files

Open a file in OS X:

$ open filename.psd
# Opens to Photoshop

Open into a certain app in OS X:

$ open -a "Adobe Photoshop 7.0" foo.jpg

Moving, renaming, and copying

Move a file:

$ mv logo.png images/logo.png

Rename a file, mv is actually a move command, we’re kinda moving the file to the same directory:

$ mv index.html index-old.html

Copy a file:

$ cp index.html index-copy.html

Move directory’s content one level up. Basically this:

Gif showing the dragging of files in OS X finder
$ mv myfolder/* .

Even better, you can chain the removal of the now empty directory with the double ampersand:

sudo mv myfolder/* . && rmdir myfolder/

Removing files

$ rm my-file.txt
rm: remove write-protected regular empty file ‘my-file.txt’?
# Answer with y or n

Remove a directory:

$ rmdir my-directory/

Remove directory recursively:

$ rm -r my-directory/

Use the force, the "rimraf". Careful with this one, it’s easy to remove too much, it won’t prompt you and the files can’t be recovered:

$ rm -rf my-directory/

Viewing and editing

Print out the contents of a file (concatenate):

$ cat foo.txt

Edit a file in your chosen text editor:

$ vim foo.txt
$ nano foo.txt
$ vsc foo.txt

Installing packages

Every system comes with its own package manager.

Using apt-get, the Debian package manager

Install packages:

$ sudo apt-get install htop

Search for packages:

$ apt-get search htop

Reinstall package:

$ sudo apt-get install --reinstall packagename

Update packages, first update the package list, then the actual packages

$ apt-get update && apt-get upgrade

See this great apt-get cheat sheet.

Using Homebrew: the Mac OS package manager

Update the Homebrew package list:

$ brew update

Install a package:

$ brew install htop

Search for packages:

$ brew search htop

Update a packages:

$ brew upgrade htop

Update all packages:

$ brew upgrade

Show all outdated packages:

$ brew outdated

Quitting processes

Kill a processe, (read more about killing). First note the PID, use htop for that, then run:

$ kill -9 <PID-HERE>

Clearing

Clear the terminal window:

$ clear

Or Ctrl+k will destroy the current buffer completely, meaning you can’t scroll up anymore.

Permissions and access

Check folder permissions:

$ ls -l ./my-dir

Change owner of a file:

$ chown my-file.txt

Change owner of a directory (recursively):

$ chown -R newowner my-dir/

Change owner and group of a directory and all its files:

$ chown -R newowner:newgroup my-dir/

Change group only:

$ chown -R :newgroup my-dir/

Add user to a group:

$ sudo usermod -a -G www-data username

Add your user to a group, to www-data in this case:

$ sudo usermod -a -G www-data username

Change permissions recursively, but to directories only. This change all directories in the current working directory to 755:

$ sudo find . -type d -print0 | xargs -0 chmod 0755

This one changes all files to 644 recursively, but doesn’t touch directories:

$ sudo find . -type f -print0 | xargs -0 chmod 0644

User switching

Switch user, comes handy in server environment (su: Switch User):

$ su username

Or switch to root with sudo:

$ sudo -i

Switch back to your original user:

$ exit

User management

Make a new user:

$ sudo useradd bob

Change currently logged in users password:

$ sudo passwd

Change other user password:

$ sudo passwd bob

Restarting, booting, and exiting

Reboot a machine, rarely needed but not never:

$ sudo reboot now
# Or only a reboot worked just as well
reboot

Turn the machine off:

$ shutdown

Or halt:

$ shutdown -H

Exit the machine or a user you’re in:

$ exit

Finding stuff

Look from the current working directory . a file named foo-bar.svg:

$ find . -name foo-bar.svg

Locate your php.ini file:

$ php --ini

Misc commands

Get the system time in Ubuntu (clock):

$ hwclock --show

Get status of a service in Ubuntu, mysql in this case:

$ service mysql status

Get all installed packages in Ubuntu:

$ dpkg --get-selections | grep -v deinstall

Reload NGINX:

$ sudo nginx -s reload

Restart any service after changing setting, NGINX in this case:

$ sudo service nginx restart

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