Posted by David Fendley in I am a diehard Linux and Mac enthusiast. One of the key reasons for this is the shell environment that both operating systems share. A powerful shell is key to any quality operating system and allows you to perform actions that can be considerably more power than a GUI.
Recently, a friend of mine asked how he could get started in learning the shell. As the shell can initially appear a bit intimidating, I decided to put together an introduction to the shell.
Getting Started
Entering the shell from a desktop environment is as easy as opening Terminal in OS X (/Applications/Utilities) or opening GnomeTerminal or Konsole in Linux (sorry Windows users. Windows has a completely worthless shell. You do have an option, though: install Cygwin. Details in the foot notes).
Upon opening your terminal application, you will be greeted with a command prompt.
Wraith:~ tricon$
Typically this prompt will consist of your computer name, current directory, user name, and end with a “$”. This “$” shows that you are logged in as a user (more on this later). Note that in this case my current directory is displayed as ~. ~ means “home directory” or “user directory”, and is where files pertaining to your user account are located.
ls
The first command to learn is one you will use frequently: ls. Type this now and hit return.
Wraith:~ tricon$ ls Complete Documents Library Pictures StoryMill Backups Zinio Library organize Desktop Downloads Movies Public Web Sync autopar.rb wo_conduit.sh Development Icon? Music Sites WebServer dwhelper Wraith:~ tricon$
ls is short for “list”. This command lists all files in the current directory.
Most commands have options. These options adjust the way a command operates or what it operates on.
A useful option for the ls command is -a. Note that - typically denotes that you are issuing options to the command in order to differentiate from a parameter. These parameters can be additional input, a file, or another form of input that the command requires (more on parameters later).
Before you re-run ls with the -a option, I’m going to teach you a very useful trick. Hit the up arrow on your keyboard. This will bring back the last command you typed. In fact, you can keep hitting the up arrow to cycle through your past commands.
Hit the up arrow and append -a to the ls command.
Wraith:~ tricon$ ls -a . .bash_history .fonts.cache-1 .lesshst .rnd .viminfo Library .. .bash_profile .gconf .macports .sabnzbd .vimperatorrc Movies .BridgeLabelsAndRatings .bashrc .gconfd .mc .sh_history .vimprojects Music .CFUserTextEncoding .bittorrent .gem .mozilla .smb .wapi Pictures .CurseClient .config .gemrc .mplayer .spumux .wine-243ASY Public .DS_Store .cpan .gitconfig .mysql_history .sqlite_history .wine-rEp0fS Sites .DownloadManager .crash_report_checksum .gitk .ncftp .ssh .zsh_history StoryMill Backups .FontForge .crash_report_frames .gnome2 .parallels_settings .sshterm .zshrc Web Sync .MacOSX .crash_report_preview .gnome2_private .profile .subversion Complete WebServer .Trash .cups .gnucash .psync.db .svk Desktop Zinio Library .Xauthority .dvdcss .gvimrc .qt .tweet Development autopar.rb .Xcode .emacs .irb_history .rails-plugin-sources .twitter Documents dwhelper .adobe .emacs.d .jedit .rdebug_hist .vim Downloads organize .banking .fontconfig .kismet .recently-used.xbel .vimfuzzyfinder Icon? wo_conduit.sh
ls -a lists all files in the current directory, including hidden ones. Files beginning with a period are considered hidden.
Now type: ls -l
Wraith:~ tricon$ ls -l total 32 rwxr-xr-x 4 tricon admin 136 Apr 11 03:52 Complete drwx------ 8 tricon staff 272 Apr 23 06:30 Desktop drwxr-xr-x 13 tricon staff 442 Apr 21 18:37 Development drwx------ 88 tricon staff 2992 Apr 18 14:18 Documents drwxr-xr-x@ 75 tricon staff 2550 Apr 23 05:29 Downloads -rw-r--r--@ 1 tricon staff 0 Nov 8 18:48 Icon? drwx------ 65 tricon staff 2210 Feb 10 20:13 Library drwx------ 9 tricon staff 306 Apr 23 06:18 Movies drwx---r-x 72 tricon staff 2448 Apr 19 22:13 Music drwx------+ 130 tricon staff 4420 Apr 23 05:20 Pictures drwxrwxrwx 8 tricon staff 272 Feb 14 17:43 Public drwxr-xr-x 5 tricon staff 170 Dec 2 22:52 Sites drwxr-xr-x 8 tricon staff 272 Apr 19 21:30 StoryMill Backups drwxr-xr-x 6 tricon staff 204 Mar 6 23:22 Web Sync lrwxr-xr-x 1 root wheel 19 Feb 10 19:42 WebServer -> /Library/WebServer/ drwxr-xr-x 7 tricon staff 238 Dec 9 17:13 Zinio Library -rwxr-xr-x@ 1 tricon staff 341 Jan 24 14:43 autopar.rb drwxr-xr-x@ 37 tricon staff 1258 Apr 23 06:42 dwhelper drwxr-xr-x 5 tricon staff 170 Jan 17 16:38 organize -rwxr-xr-x@ 1 tricon staff 120 Mar 14 06:09 wo_conduit.sh
This lists files vertically, showing their attributes (more on this later).
Now type: ls -al
Wraith:~ tricon$ ls -al total 43616 drwxr-xr-x 98 tricon staff 3332 Apr 22 22:26 . drwxr-xr-x 5 root admin 170 Jan 23 10:16 .. -rw-rw----@ 1 tricon staff 173 Aug 26 2008 .BridgeLabelsAndRatings -rw------- 1 tricon staff 3 Apr 12 2008 .CFUserTextEncoding drwxr-xr-x 6 tricon staff 204 Nov 25 00:47 .CurseClient -rw-r--r--@ 1 tricon staff 21508 Apr 23 04:47 .DS_Store drwxr-xr-x 4 tricon staff 136 Jul 3 2008 .DownloadManager drwx------ 2 tricon staff 68 Feb 1 18:32 .FontForge drwx------ 3 tricon staff 102 Apr 22 02:44 .MacOSX drwx------ 2 tricon staff 68 Apr 23 06:18 .Trash -rw------- 1 tricon staff 0 Mar 8 19:10 .Xauthority drwxr-xr-x 2 tricon staff 68 Jul 1 2008 .Xcode drwxr-x--x 3 tricon staff 102 Apr 17 2008 .adobe drwx------ 2 tricon staff 68 Jun 23 2008 .banking -rw------- 1 tricon staff 64347 Apr 22 23:31 .bash_history -rw-r--r--@ 1 tricon staff 17 Mar 4 16:54 .bash_profile -rw-r--r-- 1 tricon staff 314 Apr 16 17:27 .bashrc drwx------ 3 tricon staff 102 Sep 23 2008 .bittorrent drwxr-xr-x 4 tricon staff 136 Jun 17 2008 .config drwxr-xr-x 5 root staff 170 Jun 2 2008 .cpan -rw-r--r-- 1 tricon staff 5745 Nov 20 04:14 .crash_report_checksum -rw-r--r-- 1 tricon staff 11021 Nov 20 04:14 .crash_report_frames -rw-r--r-- 1 tricon staff 17927 Nov 20 04:14 .crash_report_preview drwx------ 3 tricon staff 102 Apr 13 2008 .cups ...
Here we provided two options to ls: -a and -l. With most commands you can append them behind a single -.
Notice that when using -a with the ls command there are two odd looking entries: . and ..
. refers to the current directory that you are in while .. refers to the parent directory — the one above the current directory. These are very useful and lead us into the next command.
cd
cd stands for “change directory”. This allows you to move between directories in the shell.
Type: cd ..
Wraith:~ tricon$ cd .. Wraith:Users tricon$
cd .. means “change to directory ..” Since .. refers to the parent directory, you just went up a directory in the shell.
Wraith:Users tricon$ ls Shared tricon
We are now in the directory for user accounts (/Users/ in OS X; /home/ in Linux). You should see your username in this listing. Here’s a neat trick. Type: cd followed by a letter or two of your username and hit the tab key. Your username was just auto-completed.
Auto-completion is a huge time saver. At any point while you are typing part of a path, you can hit tab to auto-complete the part of the path you are typing. But what happens when there are multiple possibilities? Hitting tab the first time will do nothing on the command line (thought it will typically make a beeping noise). Hitting tab again will list the possibilities. In order for tab to auto-complete, you need to type enough characters so that the possibilities are narrowed down to one, at which point hitting tab will auto-complete.
You’ve just learned two very common and important commands. This next command is one of the most important as it will allow you to learn how to use virtually any command.
man
man is short for “manual”. This command will display the manual, or “man page”, for virtually any command. Type: man ls.
You will be shown a window with all of the details you could ever want to know about the ls command. Within this screen you can use the arrow keys to navigate. Hit q to “quit” and return back to the command prompt.
Homework
For your homework, practice changing directories and listing their contents. For bonus points, practice using some of the available options listed in the man page for each command.
Final Notes
You have begun your journey to learn one of the most powerful ways to interact with a computer: the command line. While these two commands may not seem like much, they are building blocks for a shell that features hundreds of commands. These copious commands allow you to do virtually anything, from mass renaming files to looking under the hood of your operating system, automating tasks, and beyond.
In part two we’ll cover more commands, show you how to manage files from the shell, and explain what attributes are and why they are important.
Cygwin
For you Windows users out there, there is hope! Cygwin is a Linux shell environment for Windows. Upon installing this, you will be able to launch a program from your Start Menu that will provide you with a shell nearly identical to the ones available in OS X and Linux.
Cygwin can be found here: http://www.cygwin.com/
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