You can use PERL locally on your PC, or you can use it directly on the Unix system. The advantage of using it locally is that the turnaround when you run-test-run is almost instant. The advantage of using it on Unix is that when it runs, you're pretty sure it'll work as a cgi script, too.

To run perl on your PC, you'll need to download the software. A good source is ZDnet (see link below; several versions are available.) You should get Perl 5 rather than Perl 4.

Running on the PC. Once you've installed Perl in a directory (perhaps c:\perl) on your PC, just open an MS-DOS window for editing, and cd to get to c:\perl. Then use your editor to create a tiny little hello program like

print "hello again, world!\n";

then save it as prog1.pl, and open another MS-DOS window into your perl directory. type

perl prog1.pl

and it'll run. Now try adding about 3 more lines (more print statments), then injecting some syntax errors (maybe leave off the semicolon), and run it again.

Running on Unix. To run perl directly on Unix, type

/usr/local/bin/perl test.pl

assuming that your program's name is test.pl. You might try that with our hello.pl example.

You can speed  things up a bit by editing the hidden file ".cshrc" and adding this line:

alias perl /usr/local/bin/perl

The next time you log in, you will be able to just type 'perl' instead of '/usr/local/bin/perl'. (To force this capability into action right now, just login again.)

Working in the Unix environment is something you should all know how to do, but I'm not going to teach you. Go get a book, learn the ten top Unix commands and about fifteen common 'vi' editor commands, and you're in business. Do it SOON....

Basic PERL Facts

If you're fairly experienced with computers by now, you should be able to learn Perl from the examples and from Web reference information. I gave you a link to one such site (http://perl-com.songline.com/faq/)  in the syllabus. Here's another: ftp://ftp.cis.ufl.edu/pub/perl/faq/FAQa
 

Variables

Scalars (single variables) look like this:

$a = "This is an alphabetic variable.";
$n = 34.4; # A numeric variable

Anytime you use a symbol beginning with $, it's automatically declared. Variables have no special type; they take on the type of whatever is assigned to them. As you see, assignment is with the "=" operator.

Arrays are referred to as a whole in this way:

@fruit=("banana","apple","orange");

To get at these elements, we could use

print $fruit[0]."\n"; # to print banana. The dot (.) is string concatenation.

or equivalently,

print "$fruit[0]\n";

The double quotes allow the interpretation of variables within them. If you wanted to print exactly what you see (instead of the contents of $fruit[0]) you could command:

print '$fruit[0]';

The Special Variable

Perl can be thought of as a big filtering system. If you don't give it a variable, it automatically assumes that you're talking about a variable called "the current line" and symbolized by $_ (dollar underscore.)
 
For instance

$_ = "My goodness!\n";

print;

would print the contents of the special variable.
 
 Query 7.1: Experiment with perl. What would happen if you loaded up an array named @list with five items,
and then tried
 

print @list;

Control operators are few and simple.

while (boolean expression)
{stuff you want to do
}

if (boolean expression)
{stuff you want to do}
elsif (another boolean expression)
{other stuff you want to do}
elsif (yet another boolean)
{... you can stack 'em up forever. Or don't use any elsif if you don't want one.}

Example:
 

# argecho.pl -- show any command-line arguments (argument-echo)

$argNum = @ARGV;

$i = 0;

while ($i < $argNum)

{

    print $i, " -- ", $ARGV[$i], "\n";

    $i++;

}

Go make some syntax errors. It's instructive.

File i/o; pattern matching

Construct a little file named citymile.dat with these contents:

Miami, FL, Orlando, FL 257

Boston, MA, Chicago, IL, 963

Tampa, FL, Orlando, FL 105

Then construct a perl program as follows:
 

#chigo.pl -- print if line contains the word "Chicago"

while (<STDIN>)

{ print if /Chicago/;}

And stimulate it as follows:
 

perl chigo.pl < citymile.dat

It should print Boston, MA, Chicago, IL, 963

If you run it interactively, as follows
 

perl chico.pl

then type some line, which is ignored

but if you mention Chicago, it is echoed

but if you mention Chicago, it is echoed

until you type a line containing control-c to end it

^C at chico.pl line 5, <STDIN> line 6

Regular Expressions

You can fish for many things with these search strings, using  meta-characters. An example: the character "." (period) will match any character. So if you search for
 

/M.ke/

There's a whole bunch of neat search characters; I'll give you a photocopy of a list of them.

Splitting Strings

A very important capability is called 'split'. It looks like this:

@newVals = split(/-/, $valString);

This says to split the string in $valString into an array named @newVals. If $valString="yes-no-down-up", then after this split operation, @newVals will contain the following elements as $newVals[0], [1], etc:

"yes","no","down","up"

We'll do a lot with split, on Thursday.

Query 7.2: Go get Perl running on your PC if you haven't already. Try all the examples above, and make up more of your own. Read the FAQ's about Perl, and get busy learning how this stuff works!