We'll use split to get at the first line in each paragraph, and we'll number the paragraphs:

#!/usr/bin/perl

# summary.plx

use warnings;

use strict;

$/ = "";

my $counter = 1;

while (<>) {

   print $counter++, ":";

   print ((split /\n/, $_)[0]);

   print "\n";

}

When run on the beginning of this chapter, it gives the following output:

> perl summary.plx chapter6

1:We're starting to write real programs now, and real programs

2:What we want to do in this chapter is extend these techniques

3:First though, let's do some groundwork. When we're dealing

4:We've actually already seen a filehandle: the STDIN of .

5:As a counterpart to standard input, there's also standard

6:Every program has these three filehandles available, at least

>

We're assuming here that each line in the paragraph ends with a newline character rather than wrapping around to the next line. In the latter case, our program would return each of the paragraphs in their entirety, because split is being based on \n.

How It Works

This time we're reading from files specified on the command line, so we use the diamond operator. We start by putting the input record separator into paragraph mode:

$/ = "";

For every paragraph we read in, we print a new number, then get the first line of the paragraph:

print ((split /\n/, $_)[0]);

First we split the paragraph into lines, by splitting around a newline character. Since split just produces a list, we can take the first element of this list in the same way as any other.

Reading Entire Files

Finally, you may want to read a whole file into a single string. You could do this easily enough using join, but Perl provides another special value of $/ for this. If we want to say that there is no record separator, we set $/ to the undefined value. So, for instance, to read the whole of the above quotes file into a variable, we do this:

$/ = undef;

open QUOTES, "quotes.dat" or die $!;

my $file = ;

You may also see the form undef $/ doing the same job: the undef operator gives a variable the undefined value.