TweetFollow Us on Twitter

Jun 02 Section 7

Volume Number: 18 (2002)
Issue Number: 06
Column Tag: Section 7

Some Basic Commands

by Rich Morin

Learn these first; the others can wait!

Before we look at any specific commands, we need to look at some fundamental differences between BSD terminal sessions and the ordinary Mac OS X (OSX) experience. Each interface has its advantages and disadvantages; by understanding these, you'll be able to use both interfaces more effectively!

  • Applications vs. Commands OSX applications tend to be highly interactive, providing customized environments for accomplishing particular tasks. BSD commands, in contrast, are generally run in "batch mode". The user issues the command, giving all of the needed information, waits for the result, and goes on.
  • Documents vs. Files OSX documents are generally encoded in an application-specific data format. Consequently, it is only by extra effort that other applications can make use of them. BSD files are expected to be useful to a wide range of commands. As a result, they are often formatted as ASCII text files, using white space (blanks, spaces, and newlines) to delineate internal data elements.
  • Subjects vs. Verbs In OSX, the user double-clicks on the icon for a document (subject) and the appropriate application (verb) starts up. Alternatively, s/he drags the document icon (subject) over to the application icon (verb). In BSD, the user types in the name of a command (verb), followed by assorted file names (subjects) and flags (adverbs).
  • Mice vs. Keyboards OSX employs a graphical user interface (GUI), using the mouse (trackball, ...) for nearly every action. Keyboard "shortcuts" are provided in some cases, but they are never required. In BSD, the situation is exactly reversed. The keyboard is used for everything; mouse "shortcuts" are used only occasionally.
  • Windows vs. Sessions OSX applications often put up multiple windows; actions taken in one window are expected to have ramifications in all of the other windows. Each BSD terminal session, in contrast, is expected to be independent of all of the other sessions.
  • Aqua vs. The Shell Aqua (including the Dock and the Finder) allows the user to navigate through the file system, manipulate documents and folders, and start up commands. The BSD "shell" (assisted by some common commands) provides equivalent capabilities, plus others (e.g., scripting, session logging). Of course, the user interfaces vary substantially!

Navigation Commands

As noted above, BSD command lines start with a verb, followed by some number of subjects and adverbs. Last month, we used the "man" command to view manual pages; let's use it again, trying out some variations.

[localhost:~] rdm% man 2 sync
[localhost:~] rdm% man 8 sync
[localhost:~] rdm% man sync

The sync(2) manual page describes a system call; sync(8), in contrast, is a system maintenance command. By specifying the section number, we can tell man which part of the manual to search. In most cases, there is no conflict, so the section number can be left off.

None of man's "arguments" are actually file names. Instead, they are hints that allow man to search assorted directories. The actual list of directories that man examines is specified by MANPATH, a BSD "environment variable". Environment variables and control files perform many of the functions of OSX preferences:

[localhost:~] rdm% echo $MANPATH
/Users/rdm/man:/usr/local/share/man:/usr/share/man

This tells us that man looks first under /Users/rdm/man (the user's personal man pages), /usr/local/share/man (this machine's "local" man pages), and /usr/share/man (OSX man pages). Let's wander over to the latter directory and take a look:

[localhost:~] rdm% cd /usr/share/man
[localhost:/usr/share/man] rdm% ls -F
man1/      man3/      man5/      man7/      whatis.db
man2/      man4/      man6/      man8/

The cd(1) command sets /usr/share/man as the "current directory" for this terminal session. This can save a lot of typing! For convenience, the shell puts the name of the current directory in the command line's "prompt string".

The ls(1) command provides a directory listing, appending slashes to directory names (as directed by the -F option). So far, the Finder seems a lot more convenient, but hang on a bit! Let's find out which directories have "sync" man pages:

[localhost:/usr/share/man] rdm% ls */sync*
man2/sync.2  man8/sync.8

The asterisk "wild cards" tell the shell to look through every subdirectory, looking for files whose names begin with "sync". Hmm; looks like the shell has some advantages when lots of items are involved. How many pages might that be, anyway?

[localhost:/usr/share/man] rdm% ls */* | wc -l
    2853

This command "pipeline" ran two commands, directing the "standard output" of one into the "standard input" of the other. The first command listed every file in every subdirectory; the second counted the number of lines in the first command's output. The result (2853) was something which neither base command was "designed" to produce.

This pipeline is actually a minuscule instance of a "shell script". BSD users frequently write scripts to automate repetitive tasks. Next month, we'll look at some more commands and some fancier ways of writing shell scripts.


Rich Morin has been using computers since 1970, Unix since 1986, and Mac-based Unix since 1986 (when he helped Apple create A/UX 1.0). When he isn't writing this column, Rich runs Prime Time Freeware (www.ptf.com), a publisher of books and CD-ROMs for the Free and Open Source software community. Feel free to write to Rich at rdm@ptf.com.

 
AAPL
$562.29
Apple Inc.
-3.03
MSFT
$29.06
Microsoft Corpora
-0.01
GOOG
$591.53
Google Inc.
-12.13
MacTech Search:
Community Search:

SketchBook Ink Review
SketchBook Ink Review By Lisa Caplan on May 25th, 2012 Our Rating: :: SIMPLEiPad Only App - Designed for the iPad SketchBook Ink has a welcoming interface but lacks key features   Developer: Autodesk Inc. | Read more »
Autumn Dynasty Review
Autumn Dynasty Review By Kevin Stout on May 25th, 2012 Our Rating: :: NEARLY FLAWLESSiPad Only App - Designed for the iPad Autumn Dynasty is an oriental-themed real-time strategy game.   | Read more »
Our Annual “Holy Cow It’s Memorial Day A...
So, it’s that time of year again! BBQs, lawn chairs, beer, and the ability to finally wear shorts with sandals without fear of frostbite. Tan those legs and check out all the huge sales that are going on across the App Store below. We’ll try and... | Read more »
FREEday 5/25/12 – “They Call Me FREE but...
Another week of freebies, this time with very little in the way of “Big Name” titles. No need to panic, it’s intentional. Anyone browsing the App Store will no doubt see the more popular games anyway. | Read more »
Shoot the Zombirds Review
Shoot the Zombirds Review By Kevin Stout on May 25th, 2012 Our Rating: :: ADDICTINGUniversal App - Designed for iPhone and iPad Shoot the Zombirds is an archery game where the player shoots arrows at avian zombies.   | Read more »
Apple Debuts Free App of the Week Promot...
Apple has made a couple of changes to their weekly app features that pop up in the Featured tab of the App Store. While “App of the Week” and “Game of the Week” appear to be just rebranded as “Editors’ Choice,” there’s a new feature: the Free Game... | Read more »
Gun Runner Review
Gun Runner Review By Jason Wadsworth on May 25th, 2012 Our Rating: :: RUN AND GUNUniversal App - Designed for iPhone and iPad The name says it all. This clever homage to classic side-scrolling shooters is easy to enjoy but hard to... | Read more »

Price Scanner via MacPrices.net

Apple Maintains Leading Mobile Device Manufacturer...
Milennial Media says Apple continued to be the number one mobile device manufacturer on their platform in Q1, representing 28% of the top manufacturers impression share. Apple iPhone accounted for 15... Read more
Asustek To Launch Three New ZenBook Ultrabook Mode...
Digitimes’ Rebecca Kuo and Steve Shen report that PC-maker Asustek Computer will launch three new models to its ZenBook Prime Ultrabook lineup – the UX21A, UX31A and UX32VD – in June, featuring full... Read more
Yahoo! Introduces Axis Search Browser For Mobile D...
Yahoo! has announced the availability of Yahoo! Axis, a new Web browser tool that it claims will re-imagine how people search and browse on the web, Axis offering a faster, smarter search with... Read more
Android- and iOS-Powered Smartphones Expand Market...
Smartphones powered by Android and iOS mobile operating systems accounted for more than eight out of ten smartphones shipped in the first quarter of 2012 (1Q12), according to the International Data... Read more
Roundup of Memorial Day Weekend MacBook Pro sales,...
 Apple resellers have MacBook Pros on sale for up to $240 off MSRP this Holiday weekend. Here is a roundup of the best prices available from any reseller: (1) B&H Photo has MacBook Pros on sale... Read more
iPad wait times down to 1-3 days at The Apple Stor...
The Apple Store Online is now reporting a 1-3 business day wait on all iPad orders, as it appears that Apple is clearing out their backlog. The iPad is available in Wi-Fi or Wi-Fi + Cellular... Read more
Roundup of Memorial Day Weekend MacBook Air sales,...
 Apple resellers have MacBook Airs on sale for up to $101 off MSRP this Holiday weekend. Here is a roundup of the best prices available from any reseller: (1) B&H Photo has 11-inch and 13-inch... Read more
13″ 2.8GHz MacBook Pro on sale for $100 off MSRP
Adorama has lowered their price on the 13″ 2.8GHz MacBook Pro to $1399 including free shipping plus NY/NJ sales tax only. Their price is $100 off MSRP, and it’s the lowest price for this model from... Read more

Jobs Board

iPad/iPhone Developer at Recruitarrow (P...
Job Responsibilities and Requirements: These solutions must be aligned with business and IT strategies and comply with the organization's architectural standards. Involved in the full systems life... Read more
Mobile iphone App with API Connections t...
See requirements. Develop mobile app that interfaces to access database on webserver and infusionsoft through API. Desired Skills: iPhone, Mobile, Infusionsoft, API Read more
*Apple* Retail - Manager - Natick Colle...
Much more than just a place for amazing products, the Apple Retail Store serves a dazzling range of needs for its customers. Not only can users get hands-on experience Read more
XML image iPhone App at Elance.com (Uppe...
I want a similar iphone app like the following App below: /us/app/hd-tattoo-designs-catalog/id524766650?mt=8 I want a ... can tell who knows the expertise and who outsources the project to others.... Read more
iPhone Modem DSP Firmware Engineer at Ap...
Firmware Engineer to help develop our next generation of iPhone products. This position requires directly related ... to deliver high performance best in class modem for iPhone products. Strong... Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.