Mac OS X Leopard - ARCAism

Line 8 sets the variable show to the result of the defaults read com.apple.finder AppleShowAllFiles
command. defaults provides a way to access and alter Mac OS X user default settings from
the command line. In this case, we use it to read the AppleShowAllFiles value stored in the
com.apple.finder preference to determine the existing setting (0 or 1) so we can then toggle the
setting. If the AppleShowAllFiles value doesn’t exist yet in your Finder preference file, you will
get an error similar to this:
2007-06-26 12:24:00.175 defaults[1180]
The domain/default pair of (com.apple.finder, AppleShowAllFiles) does not exist
togglevis.sh: line 10: [: ==: unary operator expected
In this case you can ignore this, since the script will continue and actually create this value.
However, if you continue to get errors after this (or if you get a vastly different error), then something
else is wrong, and you should check your script closely.
Lines 10 through 16 provide a conditional if...then...else statement and provide the
expected actions based on the condition. First, in line 10 we check to see whether the show variable
(which is the set value of com.apple.finder AppleShowAllFiles) is 1; if it is, then we move on
to line 11 where we change com.apple.finder AppleShowAllFiles to 0. Then in line 12 we kill the
Finder using $1, which we set in line 6. If the condition in line 10 is false (the show variable is not
1), then we move on to the else part of the script, and in line 14 we set com.apple.finder
AppleShowAllFiles to 1 and then kill the Finder. Line 16 ends the if...then...else statement
with fi (that’s if backward).
The script ends when it runs out of things to do.
There are a few ways to run this script: one is to pass the script to the shell executable as an
argument, and the other is to make the actual script executable. Passing the script as an argument
to the shell looks like this:
leopard:~/bin scott$ sh togglevis
If you want to have access to the script easily from anywhere, though, you must first make
the script executable and make sure it’s in a directory that is included in your $PATH (as discussed
in the previous chapter). For example, we’ve placed this file in our own bin directory, which you
can see is set in our path with the following statement:
leopard:~/bin scott$ echo $PATH
/opt/local/bin:/Users/scott/bin:/usr/local/bin:/bin:/sbin:/usr/bin:/usr/sbin
To make it executable, we use the chmod command:
leopard:~/bin scott$ chmod u+x togglevis
Now provided the script is in your path, you can use togglevis as you would any command
from the command line.
Variables
Variables in shell scripts are generally reserved for use from within the script itself unless they are
explicitly exported as environmental variables. Environmental variables (which include things
like $PATH) are variables that are available to all shell scripts and programs, where shell variables
are available only within your script.
Setting a variable is quite easy; just create a variable name, and set its value like this:
aVariable=Value
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