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.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Combo Quest (Games)
Combo Quest 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Combo Quest is an epic, time tap role-playing adventure. In this unique masterpiece, you are a knight on a heroic quest to retrieve... | Read more »
Hero Emblems (Games)
Hero Emblems 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ** 25% OFF for a limited time to celebrate the release ** ** Note for iPhone 6 user: If it doesn't run fullscreen on your device... | Read more »
Puzzle Blitz (Games)
Puzzle Blitz 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Puzzle Blitz is a frantic puzzle solving race against the clock! Solve as many puzzles as you can, before time runs out! You have... | Read more »
Sky Patrol (Games)
Sky Patrol 1.0.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.1 (iTunes) Description: 'Strategic Twist On The Classic Shooter Genre' - Indie Game Mag... | Read more »
The Princess Bride - The Official Game...
The Princess Bride - The Official Game 1.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: An epic game based on the beloved classic movie? Inconceivable! Play the world of The Princess Bride... | Read more »
Frozen Synapse (Games)
Frozen Synapse 1.0 Device: iOS iPhone Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Frozen Synapse is a multi-award-winning tactical game. (Full cross-play with desktop and tablet versions) 9/10 Edge 9/10 Eurogamer... | Read more »
Space Marshals (Games)
Space Marshals 1.0.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: ### IMPORTANT ### Please note that iPhone 4 is not supported. Space Marshals is a Sci-fi Wild West adventure taking place... | Read more »
Battle Slimes (Games)
Battle Slimes 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: BATTLE SLIMES is a fun local multiplayer game. Control speedy & bouncy slime blobs as you compete with friends and family.... | Read more »
Spectrum - 3D Avenue (Games)
Spectrum - 3D Avenue 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: "Spectrum is a pretty cool take on twitchy/reaction-based gameplay with enough complexity and style to stand out from the... | Read more »
Drop Wizard (Games)
Drop Wizard 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Bring back the joy of arcade games! Drop Wizard is an action arcade game where you play as Teo, a wizard on a quest to save his... | Read more »

Price Scanner via MacPrices.net

Apple’s M4 Mac minis on sale for record-low p...
B&H Photo has M4 and M4 Pro Mac minis in stock and on sale right now for up to $150 off Apple’s MSRP, each including free 1-2 day shipping to most US addresses. Prices start at only $469: – M4... Read more
Deal Alert! Mac Studio with M4 Max CPU on sal...
B&H Photo has the standard-configuration Mac Studio model with Apple’s M4 Max CPU in stock today and on sale for $300 off MSRP, now $1699 (10-Core CPU and 32GB RAM/512GB SSD). B&H also... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.