Mac OS X Leopard - ARCAism

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CHAPTER 19 EXTENDING THE POWER OF DARWIN
1: #!/bin/sh
2:
3: # togglevis
4: # A shell script to toggle the visibility of hidden files in the Finder
5:
6: set `ps acx | grep Finder`
7:
8: show=`defaults read com.apple.finder AppleShowAllFiles`
9:
10: if [ $show -eq 1 ]; then
11: defaults write com.apple.finder AppleShowAllFiles 0
12: kill $1
13: else
14: defaults write com.apple.finder AppleShowAllFiles 1
15: kill $1
16: fi
NOTE For those of you who really hate line numbers in programs because they prevent you
from copying the text out of an e-book and running it, later in this chapter there will be a Perl
script that you should be able to tweak (when you are done with this chapter) to strip them out
automatically.
This script will toggle the visibility of hidden items in the Mac OS X Finder, which is done
by setting the hidden Finder preference AppleShowAllFiles to 1 (to show all files) or 0 (to hide
hidden files) and then restarting the Finder to immediately enact the change.
NOTE Truth be told, this script doesn’t exactly restart the Finder. The script instead just kills
the Finder. OS X, depending on the Finder, notices this and restarts the Finder for you.
The first line, #!/bin/sh, often referred to as the interpreter line, is important for all scripts
because it points the shell to the executing script interpreter.
NOTE On Leopard, /bin/sh and /bin/bash are both Bash shell executables. Most shell scripts
in OS X (and generally in Unix) are written for the Bourne shell (sh) for compatibility across various
Unix platforms (of which almost all have the Bourne shell installed). The Bash shell itself
(a.k.a. Bourne Again SHell) is 100 percent backward compatible with the Bourne shell, with
some extra features borrowed from the C shell and Korn shell. The general scripting syntax we
are covering in this chapter is mostly Bourne shell compatible; however, there may be certain
commands issued inside a script that are specific to OS X.
Lines 3 and 4, like all script lines beginning with # (except the sh-bang line), are comments.
These are included to provide a clue about what’s going on for anyone reading the script. Comments
have no effect on how the script runs and in this respect are purely optional elements. It is
a good habit to use comments, not only for others who may be looking at your script but also for
yourself should you have to look at a script weeks, months, or even years after you wrote it.
Here the first comment line gives the name of the script, and the second comment describes what
the script does.
Line 6 shows us two things, the use of the set command and the use of backticks (`) in
scripts. In a shell script, anything within backticks is executed, and the result is passed to the
script (this is called command substitution). The set command sets the arguments used in the
script just as if they were entered at the command line. So, line 6 takes the results from the ps acx
| grep Finder command (which would be something like 261 ?? S 0:00.93 Finder) and
makes them our arguments (of which there would be 5). The importance of line 6 for the rest of
the script is that it specifically assigns the PID of the Finder to our first argument that can then
be accessed as the variable $1.