TweetFollow Us on Twitter

Command Line Interface

Volume Number: 16 (2000)
Issue Number: 10
Column Tag: Mac OS X

An Intro to Mac OS X's Command Line Interface

by Andrew C. Stone

Back in the mid to late eighties, DOS was king and PC users would make fun of the "MacInToy" simply because it had no expert command line interface (CLI). Of course, this was before the PC world ditched their own command line interface in favor of an uglied-down graphical user interface that poorly copied the Macintosh's finely detailed GUI. Being an old Unix weenie from the academic Computer Science scene, I can understand the argument that the command line is an extremely powerful tool for expert users and programmers. Of course I also understand that it needs to be hidden from the casual user, lest they type "rm -rf /" as root and totally erase their hard disk!

And now, the CLI is just one more compelling feature of Mac OS X. OS X is based on Darwin, Apple's version of the open source FreeBSD 3.x combined with the Carnegie Melon University Mach 3.x kernel. The command line and all the standard Unix utilities are part and parcel of the developer distribution. While it is still not clear what will or won't ship to the end user in the final OS X, DP4 gives you Terminal.app (/System/Administration/Terminal.app) to provide a "shell" allowing you to type commands directly to the computer for both interactive and batch processing. This article is an introduction into the use of the command line, and I hope to provide enough information to convince unrepentent GUI freaks that a CLI is indeed useful, and share some cool tricks, tips and information on where to go to learn more.

She Sells C-shells

Once upon a time, there was just the c-shell, /bin/csh. However, Unix hackers love to cram more and more features into any one given program, so now there are several shell programs to pick from, including: tcsh, csh, zsh and bash. When you double-click Terminal.app to launch a shell, Terminal uses your default shell as the command line interface. In a standard installation, the default shell is tcsh. Your default shell is stored in NetInfo, and can be set by editing the User in /System/Administration/NetworkManager.app. Click on "Users", then select a user, then edit the shell field to the complete path of your desired default shell. You can always switch shells on the fly by just typing the name of new shell. Each shell has its strengths and supporters - you might play around to see which one you prefer. I use bash whenever I need to be able to include newlines (returns) in a command - and it handles filenames with embedded spaces rather well. Each of the various shells share a lot in common, but syntax does vary from shell to shell, so I'll just use the most basic examples here which at least apply to csh. In any regard, launch Terminal.app so you can start to play!

Man - the manual pages

One of the Unix shell's most useful features is the builtin manual pages, which document all the commands. Before we learn about "man", a short discussion of why Unix uses such cryptic and abbreviated names is in order! If you have some familiarity with DOS, you'll know that to copy a file, you type:

   copy <FILE_1> <FILE_2>

The same command in Unix is "cp". It seems early Unix programmers hated to type and loved lacunae - and you'll learn Unix shell programming faster if you can uncover the mnemonic embedded in each command. For example, csh = C shell; mv = move; ln = link; ls = list; mkdir = make directory; etc. But the cool thing is that you don't have to remember much to use Unix because the man pages detail the use of every Unix command. For example, to learn about the manual pages, type:

   man man

You'll see something like:

MAN(1)      System Reference Manual      MAN(1)

NAME
   man - display the on-line manual pages

SYNOPSIS
   man [-achw] [-C file] [-M path] [-m path] [section] name ...

DESCRIPTION
   The man utility displays the BSD Unix manual pages 
   entitled name.

The options are as follows:

   -a Display all of the manual pages for a 
   specified section and name combination. 
   (Normally, only the first manual page found is displayed.)
   ....

When you can't remember the command that you want to learn about, you can always try the apropos command, which searches the man pages' names for the given word. For example, typing

apropos directory

gives back a list of Unix commands whose description includes "directory" (directory is the Unix term for folder).


DirHandle(3)         - supply object methods for directory handles
FindBin(3)            - Locate directory of original perl script
Tcl_TranslateFileName(3)   - convert file name to native form and replace tilde 
with home directory
basename(1), dirname(1)   - return filename or directory                                   
portion of pathname
cd(1)                  - change working directory
cd(n)                  - Change working directory
chdir(2), fchdir(2)   - change current working directory
chroot(2)               - change root directory
chroot(8)               - change root directory
dir(5), dirent(5)      - directory file format
directory(3), opendir(3), readdir(3), telldir(3), seekdir(3), rewinddir(3), 
closedir(3), dirfd(3) - directory operations
ditto(8)               - copy source directories to destination                               
directory
getcwd(3)            - get pathname of current working directory
getcwd(3), getwd(3)   - get working directory pathname
getdirentries(2)   - get directory entries in a filesystem                               
independent format
ls(1)            - list directory contents
mkdir(2)         - make a directory file
mtree(8)         - map a directory hierarchy
nifind(1)      - find a directory in the NetInfo hierarchy
pax(1)            - read and write file archives and copy                         
directory hierarchies
pwd(1)            - return working directory name
pwd(n)            - Return the current working directory
remove(3)      - remove directory entry
rm(1)            - remove directory entries
rmdir(2)         - remove a directory file
scandir(3), alphasort(3) - scan a directory
unlink(2)      - remove directory entry
whois(1)         - Internet user name directory service

Apropos reveals the rich set of commands available to both the command line user and C programmer . The number following the command indicates which man subdirectory should be consulted. To read about a man page in a particular subsection, for example, scandir(3), you'd type:

   man 3 scandir

If you just typed that in, you'll notice that it's actually a C language prototype, and not really available as a command line call! If the subdirectory is 1, it's a shell command; otherwise it's a C function. Still, most standard C library functions are exposed as callable binary programs or shell scripts.

Anatomy of a Shell Command

After looking at a few Unix man pages, you'll notice that a consistent style is used to make it easy to grasp the functionality and options of a command. The simplest example is a command which takes no flags or arguments, for example:

   date

A flag modifies how the command works and is represented by a letter or digit which follows a "-" (dash) or another flag. Arguments are input to the command, such as filenames or folders:

cp -rf /bin/cat /tmp/catty
-  - ---- -----
command  flags   argument 1         argument 2

The man page presents a synopsis of the command in a standardized notation to express when a flag or argument is optional and/or repeatable. Let's look at the first example of the synopsis of "man" to learn how to decode the notation:

man [-achw] [-C file] [-M path] [-m path] [section] name ...

Anything enclosed within "[" and "]" represents optional flags and arguments. For example you could include -a or -c or -ac or -ca or -achw as valid flags to the man command.

When a word follows a flag, you must provide an argument if you use that flag. For example [-M path] means that if you use the optional -M flag, you must follow it with a full path name.

If you see ellipses, such as at the end of the synopsis, it means you can provide any number of additional names as arguments to the command.

All of the flags and arguments are described in the body of the man page for the command. Also, at the end of the man page is a section which gives additional related commands. For instance, on man's man page, you would find:

SEE ALSO
apropos(1),  whatis(1),  whereis(1),  man.conf(5),  mdoc(7),  mdoc.samples(7)

Do a "man" on some of these to keep learning more.

Less Typing, More Power

Power users, who are always looking for ways to maximize the amount accomplished with a minimal amount of typing, use initialization files to personalize their shells. Initialization files contain environmental variables, aliases, and other customizations, such as a clever shell prompt. Each shell program looks for a different initialization file; for example, csh uses ~/.cshrc and bash uses ~/.bashrc. Extra Credit: using man, find the name of the initialization file for tsch!

Aliases are short cuts to make complex commands that you use available with just a few typed characters. For example, let's say you always want to see your directory files listed in reverse order of the time created, that is, with the newest files listed at the top with the long listing:

   ls -lt 

You could add this line to your ~/.cshrc file:

   alias lt "ls -lt"

Next time you start a c shell (or type the command "source ~/.cshrc" to reread the initialization file), when you type "lt", you'll get the equivalent of typing "ls -lt". People love to put gnarly prompt creation commands in their init files, and this example is about as scary as they get:

alias cd 'cd \!*; set currDir = 'basename $cwd'; set currDir = 'echo "<${host}:"$currDir
" ! >"'; set prompt = "${currDir} "'
cd $cwd

This produces a lovely, palatable prompt which tells you which machine you are on, which directory you are in, and the number of the current command, for example:

<hermione:Developer 24 >

Which leads us to a discussion of typing less through use of history and command substitution. Your "history" is a record of the commands you've issued. Type

   history

to see a numbered list of the commands you have typed recently:

     1  cd
     2  cd Library/Preferences/
     3  rm ApplicationCacheTheFinalChapter
     4  ps -axw | grep Mail
     5  man man
     6  apropos link
     7  apropos time
     8  apropos link
     9  apropos directory

To repeat a previous command, for example, "man man", simply type:

   !5

!5 is pronounced "BANG-5" in Unix. A "*" is "splat". A "|" is a pipe, although French Surrealist painter Renð Magritte would say, "Ce n'est pas un pipe"!

To repeat the last command issued, type:

   !!

To refer to the last argument of the last command, use"!$". For example:

   cat !$

displays the contents of the last file you referenced in your last command.

In some shells, you can use your up and down arrow keys to repeat commands issued before.

Because many shell commands operate on files, and because typing file names is tedious and prone to error, you have various shortcut options.

Most shells have builtin "escape completion" which will complete the names of files and folders if you type the first few unique characters and then type your escape completion key (this might be "ESC" or F5 or even TAB in some shells). The vanilla C shell has this turned off by default, but you can add the following line to your .cshrc file to enable escape completion:

   set filec

As of DP4, the default shell is tsch, which has escape completion on. Type two escapes if one escape doesn't complete anything.

And, for you GUI junkies, OS X lets you drag and drop files or folders from the Finder onto shells, instead of laboriously typing out entire path names. You'll even get the correct escape codes for spaces, or perhaps the whole path will be correctly quoted. Because the shell interprets "words" (alphanumberic strings separated by spaces or tabs), you need to use to either "escape" the characters with a backslash:

   cd /Mac\ OS\ X

or type it with quotes:

   cd "/Mac OS X"

Bulk Processing and Iterations

Where a CLI has it all over a GUI is when you need to perform some boring, repetitve task on a bunch of files. For example, suppose you want to change the path extension of a whole folder full of files, say from ".TIF" to ".tiff" You can't do this in a GUI without an additional program, but in the C shell, you can use a simple looping shell command, using the "foreach" statement. Type:

   foreach i ( *.TIF )

At this point, you enter an interactive subshell with a new prompt, " ? ". You can type any number of commands for sequential processing, referring to the current file as $i, and the "root" of that file ($i:r), ie, the filename's full path removing it's path extension. See "man cshrc" for more info on referring to parts of a file path. Finally, when you are finished issuing commands, type end and computation begins.

? echo $i            // which file are we on? We'll print it out
? mv $i $i:r.tiff   // move that file to the same name, less extension, plus .tiff
? end                  // this terminates the loop and begins processing

Plumbing: Input, Output and Pipes

Unix is designed for hooking up the output from one process to the input of another. This is done through two basic mechanisms: redirection of standard input/standard output and pipes.

The less than symbol, "<", means take input from whatever is producing output on the right hand side of the "<". For example, you can use the command line "mail" to send ascii files:

   mail harry@stone.com < /etc/hostconfig

You can use I/O redirection whenever a command expects standard input (stdin) or produces standard output (stdout). When a process expects a feed of input, then you must rely on the chaining of processes through pipes. Pipes can be used effectively with gnutar to copy large trees of files to new locations:

   (/usr/bin/gnutar chf - Stone_CD) | (cd /BackUp; /usr/bin/gnutar xf -)

Note how you can also stage commands by separating them with a ";". Here, we are creating a new "tar" archive, changing to a new directory, and then unarchiving it to standard out, thus copying the original hierarchy of files to this new location.

Once you get the hang of Unix, you'll find that you can do all sorts of tasks. For example, the age old bean counting task of counting lines of code can be done trivially using the powerful and confusing "find" piped to the meta-command "xargs" which calls the word count program "wc". Assuming you have changed directory to the top level of your source code, type:

   find . -name '*.[hmc]' | xargs wc -l

which translates to: beginning at the top level in this current directory, recursively find all files which end in either .h, .c or .m, and use each file found as the input to the word counting program, with the option of counting only lines (not words or characters), with the bonus of providing a grand total of lines. What may look like jibberish will soon become recognizable and habitual!

And, for authors paid by the word and to honor the oft times obfuscated nature of Unix, here's an alias for your initialization file:

alias wordcount
(cat !* | tr -s '       .,;:?!()[]"' '\012' | cat -n | tail -1 | awk '{print $1}')

and you would use it in a source directory by typing:

   wordcount *.[hmc]

To go "deeper" you just add on more arguments:

   wordcount *.[hmc] */*[hmc] */*/*[hmc]

Conclusion

It takes years to learn Unix completely, but only moments to learn enough to be useful. The online man pages allow a quick refresher course in any command and are an excellent lifetime teaching tool. The shell is a power user's friend and can expand the capabilities and productivity of OS X. Granted that it is not for everyone, but for those who dare, it's a true bonus!


Andrew Stone <andrew@stone.com> is founder of Stone Design Corp <http://www.stone.com/> and has spent 12 years writing Cocoa software in its various incarnations.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Lyn 1.8.5 - Lightweight image browser an...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more
Apple iOS 10.2.1 - The latest version of...
iOS 10 is the biggest release of iOS ever. A massive update to Messages brings the power of the App Store to your conversations and makes messaging more personal than ever. Find your route with... Read more
Apple Security Update 2016-003 Supplemen...
Apple Security Update is recommended for all users and improves the security of OS X. For detailed information about the security content of this update, please visit: http://support.apple.com/kb/... Read more
Apple macOS Sierra 10.12.3 - The latest...
With Apple macOS Sierra, Siri makes its debut on Mac, with new features designed just for the desktop. Your Mac works with iCloud and your Apple devices in smart new ways, and intelligent... Read more
BetterTouchTool 1.992 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
Viber 6.5.5 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device, so... Read more
Opera 42.0.2393.137 - High-performance W...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
iClock Pro 3.4.7 - Customize your menuba...
iClock Pro is a menu bar replacement clock for Apple's default clock. iClock Pro is an update, total rewrite and improvement to the popular iClock. Have the day, date and time in different fonts and... Read more
PhotoDesk 4.1.5 - Instagram client for p...
PhotoDesk lets you view, like, comment, and download Instagram pictures/videos. (NO Uploads! / Image Posting! Instagram forbids that! AND you need an existing Instagram account). But you can do so... Read more
Capo 3.5.1 - Slow down and learn to play...
Capo lets you slow down your favorite songs so you can hear the notes and learn how they are played. With Capo, you can quickly tab out your songs atop a highly-detailed OpenCL-powered spectrogram... Read more

Clash Royale gets some serious balance u...
| Read more »
Ironhide Game Studio prepares for a busy...
Kingdom Rush breathed fresh life into the tired tower defense genre way back in 2012. The game was a robust challenge that somehow managed to lift you up, rather than leaving you feeling crushed and hopeless. The rich array of unit types and... | Read more »
Collect pets and sling arrows in Arcane...
Mobile gaming is a crowded market, but regular updates are a good way to keep us attention-short players keen. The brand new content in Arcane Online is a prime example. Published by Japanese developer Gala, Arcane Online is a fantasy MMO that... | Read more »
Super Mario Run dashes onto Android in M...
Super Mario Run was one of the biggest mobile launches in 2016 before it was met with a lukewarm response by many. While the game itself plays a treat, it's pretty hard to swallow the steep price for the full game. With that said, Android users... | Read more »
WarFriends Beginner's Guide: How to...
Chillingo's new game, WarFriends, is finally available world wide, and so far it's a refreshing change from common mobile game trends. The game's a mix of tower defense, third person shooter, and collectible card game. There's a lot to unpack here... | Read more »
Super Gridland (Entertainment)
Super Gridland 1.0 Device: iOS Universal Category: Entertainment Price: $1.99, Version: 1.0 (iTunes) Description: Match. Build. Survive. "exquisitely tuned" - Rock Paper Shotgun No in-app purches, and no ads! | Read more »
Red's Kingdom (Games)
Red's Kingdom 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Mad King Mac has kidnapped your father and stolen your golden nut! Solve puzzles and battle goons as you explore and battle your... | Read more »
Turbo League Guide: How to tame the cont...
| Read more »
Fire Emblem: Heroes coming to Google Pla...
Nintendo gave us our first look at Fire Emblem: Heroes, the upcoming mobile Fire Emblem game the company hinted at last year. Revealed at the Fire Emblem Direct event held today, the game will condense the series' tactical RPG combat into bite-... | Read more »
ReSlice (Music)
ReSlice 1.0 Device: iOS Universal Category: Music Price: $9.99, Version: 1.0 (iTunes) Description: Audio Slice Machine Slice your audio samples with ReSlice and create flexible musical atoms which can be triggered by MIDI notes or... | Read more »

Price Scanner via MacPrices.net

Deal alert! 13-inch 2.0GHz MacBook Pros for $...
B&H Photo has the new 2016 13″ 2.0GHz non-Touch Bar MacBook Pros in stock today and on sale for $225 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.0GHz MacBook Pro... Read more
Free LibreOffice Portable 5.2.4 Complete Offi...
PortableApps.com and The Document Foundation have announce the release of LibreOffice Portable 5.2.4. LibreOffice Portable is an Open Source full-featured office suite — including a word processor,... Read more
Apple Planning Three New Tablets For 2017 – D...
Digitimes’ Rebecca Kuo and Joseph Tsai say that unnamed insider sources report Apple having three new tablets in the pipeline for 2017 release: a 9.7-inch model with a friendly price range, a new mid... Read more
Roundup of 15-inch Touch Bar MacBook Pro sale...
B&H Photo has the new 2016 15″ Apple Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.7GHz Touch Bar... Read more
Apple refurbished iPad Pros available for up...
Apple has Certified Refurbished 9″ and 12″ Apple iPad Pros available for up to $160 off the cost of new iPads. An Apple one-year warranty is included with each model, and shipping is free: - 32GB 9″... Read more
16GB iPad Air 2, Apple refurbished, available...
Apple has Certified Refurbished 16GB iPad Air 2s available for $319 including free shipping. A standard Apple one-year is included. Their price is $60 off original MSRP for this model. Read more
Apple iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ and 27″ Apple iMacs on sale for up to $120 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2199 $100 off MSRP - 27″ 3.2GHz/1TB Fusion iMac... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more
Save up to $350 with Apple Certified Refurbis...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more
2015 12-inch Retina MacBooks, Apple refurbish...
Apple has Certified Refurbished 2015 12″ Retina MacBooks available for up to $410 off original MSRP. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The... Read more

Jobs Board

*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Manhattan, NY Introduction: We have immediate job openings for several Desktop Support Technicians with one of our most Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Stamford, CT We have immediate job openings for several Desktop Support Technicians with one of our most well-known Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Site Security Manager - Apple (Unite...
# Apple Site Security Manager Job Number: 54692472 Culver City, California, United States Posted: Jan. 19, 2017 Weekly Hours: 40.00 **Job Summary** The Apple Read more
*Apple* macOS Systems Integration Administra...
…most exceptional support available in the industry. SCI is seeking an Junior Apple macOS systems integration administrator that will be responsible for providing Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.