Mac OS X Leopard - ARCAism

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CHAPTER 19 EXTENDING THE POWER OF DARWIN
If our counter is set up properly (and there aren’t any other glitches in our script), line 15
will run on the last of our input values, also printing it surrounded by quotes, but then instead of
placing a comma (as if to continue the list), it will print out a . and then a newline character.
Line 16 then ends the if statement, and line 17 ends the loop and thus our little script.
One thing not shown here is that the read command can actually assign different variables
to the input, where, for example, each input value would be assigned its own variable . . . well,
that is if we assume that the number of variables and the number of words are the same. If we
had the following read statement:
read a b c
and entered this:
one two three
then $a would be assigned the value one, $b would be assigned the value two, and $c would be
assigned the value three. In the event we set read to accept three variables and we get four or
more input terms, the last read variable will absorb all the remaining values.
TIP If the integrity of your read variables is important and you want to protect against additional
input, you could assign an additional read variable to suck up all the extra data. So if you
really wanted only three input values, you could set up read with four variables and then just
use the first three, thus essentially ignoring all the excess input.
One final useful related tidbit is the ability to merge an entire file into a script. This is done
quite easily with the dot (that is, period) command. If you paid attention, you saw this in our
sample .bash_profile file toward the end of the previous chapter where we used this:
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
Here we first check to see whether our desired file (.bashrc) exists and is a normal file. If so,
we include it with the . ~/.bashrc. And that’s it. This is a handy way to create complex scripts
where you can write entire parts as separate files and then include them all together to effectively
run as one.
CAUTION If you do combine scripts together, be careful with your variables. If two different
script files use the same variable names and are then included together, unexpected (often
bad) things can happen.
Advanced Scripting with Perl, Python,
and Ruby
Shell scripting is very useful and fairly powerful for many things; however, there are a number of
more powerful languages for writing scripts than the shell. Leopard comes with three of the
biggest and most powerful scripting languages in use today: Perl, Python, and Ruby. Given the
breadth of these languages (which are often referred to as interpreted programming languages or
very high-level languages [VHLLs], rather than just scripting languages), it would be impossible
to properly teach you how to use them in all their glory in this chapter. Although these languages
are fairly easy to learn to use (some perhaps more so than others), the space (and time) needed to