Project99.OS XSpecific Commands

Project 99. OS XSpecific Commands

"What Mac OS Xspecific commands might I find useful?"

This project illustrates miscellaneous and useful commands that are specific to Mac OS X Unix. It covers the ditto, screencapture, SetFile, GetFileInfo, defaults, and plutil commands.

Other Mac OS Xspecific commands are covered elsewhere in this book. They are

• pmset to report and change power management settings (Project 37)

• system_profiler to report on the hardware and software configuration of your Mac (Project 37)

• softwareupdate to update Mac OS X from the command line (Project 38)

• nvram to report and change NV-RAM settings (Project 38)

• dscl, nifind, and nireport to operate on information in the Directory Services database, such as user-account details (Project 65)

• diskutility to manage locally mounted disks (Projects 67 and 68)

• pbcopy and pbpaste to copy and paste text between the command line and the pasteboard, or clipboard (Project 97)

• open to open Mac OS X files, folders, and graphical applications from the command line (Project 98)

Copy with ditto

The ditto command recursively copies directories and files, preserving permissions and timestamps in a similar way to the Unix command cp -pr. In versions of Mac OS X before 10.4 (Tiger), ditto must be used in preference to cp to copy files that have resource forks, which the Unix cp command did not preserve.

In the next example, we copy the entire letters directory and any subdirectories it contains to a new directory called letter.bak, preserving resource forks by passing the option --rsrc.

$ ditto --rsrc letters letters.bak

Learn More

Refer to Project 2 to learn about recursion and how to copy directories recursively by using the cp command.

In Mac OS X 10.4, ditto is less useful because cp, and most other Unix commands, now preserve HFS+ metadata, including resource forks. In a role reversal, ditto can be used to strip HFS+ metadata when passed the option --norsrc. Use this feature to trim the fat when preparing files for transfer to non-HFS+ file systems.

The ditto command provides other useful options. Specify -V (verbose) to tell ditto to echo the name of each file as it is copied. Options also create and extract Unix cpio archives and PKZip archives for Windows compatibility: Read the man page for more details on these options.

Note

In Mac OS X 10.4, the --rsrc option is switched on by default. In previous versions, it was switched off by default.

A difference in the ways that ditto and cp behave can cause confusion. Both create the target directory when it does not exist. When the target directory does exist, ditto performs the copy in exactly the same way. The cp command, however, creates a new directory within an existent target directory, named after the source directory, and copies into that instead.

If you've installed Apple's Developer Tools, you'll find a command called CpMac, which copies files preserving resource forks and attributes just as ditto does.

$ /Developer/Tools/CpMac usage: CpMac [-r] [-p] <source-path> <dest-path>        CpMac [-r] [-p] <source-path>... <dest-dir>

CpMac has a Unix man page, but remember to type man CpMac and not man cpmac.

Snap with Screen Capture

The screencapture command provides functionality equivalent to pressing Command-Shift-4, taking a snapshot of the screen. It has many options, including an interactive mode, but of greatest use for the command line and scripting is its "hands-free" mode, in which it operates without user intervention. To take a screen shot, specify option -x to silence the sound effects and provide a filename. For example:

$ screencapture -x ~/Desktop/p1.png

The default image format is PNG (Portable Network Graphics)hence, our chosen file extension.

Other useful options include -C to capture the cursor and -c to capture to the clipboard (in which case a filename is not necessary). Also, change the format of captured images by passing the -t option. Here are some examples, in which you can guess the chosen image format.

$ screencapture -xC -ttiff ~/Desktop/p1.tiff $ screencapture -xC -tjpeg ~/Desktop/p1.jpg $ screencapture -xC -tpdf ~/Desktop/p1.pdf

To check that the file format is as expected, use the file command.

$ file ~/Desktop/p1.tiff /Users/saruman/Desktop/p1.tiff: TIFF image data, big-endian

Just for fun, here's a trick in which we take a snapshot of the login screen while logged out. Issue the following command and then log out, allowing Terminal to terminate. Make sure that the login screen is showing 60 seconds after issuing the commands.

$ sudo -s Password: (admin password here) $ nohup bash -c "sleep 60; ¬      screencapture ~/Pictures/screen.pdf"

To create time-delayed screen shots, use screencapture in combination with the at command (see Project 70).

Manage HFS+ File Attributes

If you've installed Apple's Developer Tools, you'll have two commands that view and set HFS+ file attributes. Such attributes include a file's Mac OS type and creator codes, and the hide-file-extension attribute (where the Finder hides the file's extension). We won't explain the meanings of HFS+ attributes; we'll just present examples showing how you might view and set them.

To display a brief usage summary, issue the SetFile command with no parameters.

$ /Developer/Tools/SetFile Usage: SetFile [option...] file...   -a attributes # attributes (lowercase = 0, uppercase = 1)* ...          E    Hidden extension* ...          Z    Busy* ...

Display the HFS+ attributes for a file named p1.jpg by typing

$ /Developer/Tools/GetFileInfo p1.jpg file: "/Users/saruman/Desktop/p1.jpg" type: "" creator: "" attributes: avbstclinmEdz created: 10/17/2005 10:11:12 modified: 10/17/2005 10:11:12

The capital E in the attributes list tells us that the extension is hidden (the hide-file-extension attribute is switched on), and the filename shows as p1 in the Finder. To make the extension visible, type

$ /Developer/Tools/SetFile -a e p1.jpg

A lowercase letter e switches off the hide-file-extension attribute. View the file in the Finder, and you'll see that its name now shows as p1.jpg. (You might have to click the file icon to make the Finder refresh before the extension shows.)

To switch the attribute back on and hide the extension, type

$ /Developer/Tools/SetFile -a E p1.jpg

Read and Set Preferences Files

Your personal preference settings are stored in plist files (files with the extension .plist) in the directory ~/Library/Preferences. System preferences applicable to all users are in the directory /Library/Preferences. In versions of Mac OS X before 10.4 (Tiger), preferences are stored in XML (eXtensible Markup Language) format. Preferences in Tiger are stored in binary format.

Tip

Some preferences are not shown in an application's Preferences window but can be discovered and changed with defaults. If you want to try experimental settings, be sure to save a copy of the original preferences file first.

It's possible to examine and change preferences settings from the command line with the defaults command. To examine preferences, such as your personal preferences settings for iChat, type

$ defaults read ~/Library/Preferences/com.apple.iChat {     ABDirectoryResultColumnTitle = "Instant Messaging";     AccountSortOrder = ("90AFA166-D274-4514-9358-136AEF...     AutoReplyWithAway = 0;     AutosaveChats = 1;     AwayOnFastUserSwitch = 1;     BuddyInfoSelectedTab = 0;     "BuddyList.EnableGroups" = 0;     "BuddyList.Visible" = 1; ...

(Notice that we don't include the extension in the filename given to defaults.)

Most of the preferences settings can be related to those in the application's Preferences window, accessed from its Preferences menu. In the next example, we set the preference AwayOnFastUserSwitch to 0 (off or FALSE).

$ defaults write ~/Library/Preferences/com.apple.iChat ¬     AwayOnFastUserSwitch 0

You'll have to explore preferences files to determine what settings an application has and what values they can be set to.

Manage Preferences Files

Use the plutil command to check and convert preferences files. The next example checks all preferences files in the directory ~/Library/Preferences for signs of corruption. Specify the -lint option to plutil and option -s to report only on preferences files that fail the check.

$ plutil -lint -s ~/Library/Preferences/*.plist 2005-10-17 11:57:22.847 plutil[6653] CFLog (0):    CFPropertyListCreateFromXMLData(): plist parse failed;    the data is not proper UTF-8. The file name for this    data could be:    com.apple.help.plist    The parser will retry as in 10.2, but the problem should    be corrected in the plist.    com.apple.help.plist: Conversion of data failed. The file is not UTF-8, or in the encoding specified in XML header if XML.

This command provides a handy integrity check of application preferences, to be run when applications start to act strangely or fail to start up.

To convert a preferences file's contents between XML and the new Tiger binary format, specify the -convert option. We might want to make a binary Tiger preferences file readable in a text editor by converting it to XML.

$ plutil -convert xml1 ¬     ~/Library/Preferences/com.apple.TextEdit.plist

A Tiger application can read both formats, but tests show that applications rewrite their preferences files in binary format.

To convert back to binary format manually, type

$ plutil -convert binary1 ¬     ~/Library/Preferences/com.apple.TextEdit.plist