perlretut: Add some introductory remarks

In re-reading this, I realized that it assumed some basic knowledge, so
this commit adds text to explain what formerly was assumed.

1 files changed, 30 insertions, 9 deletions

diff --git a/pod/perlretut.pod b/pod/perlretut.pod
index 734ca5cfb3..d74276c91d 100644
--- a/pod/perlretut.pod
+++ b/pod/perlretut.pod
@@ -17,21 +17,42 @@ expressions display an efficiency and flexibility unknown in most
 other computer languages.  Mastering even the basics of regular
 expressions will allow you to manipulate text with surprising ease.
 
-What is a regular expression?  A regular expression is simply a string
-that describes a pattern.  Patterns are in common use these days;
+What is a regular expression?  At its most basic, a regular expression
+is a template that is used to determine if a string has certain
+characteristics.  The string is most often some text, such as a line,
+sentence, web page, or even a whole book, but less commonly it could be
+some binary data as well.
+Suppose we want to determine if the text in variable, C<$var> contains
+the sequence of characters C<m> C<u> C<s> C<h> C<r> C<o> C<o> C<m>
+(blanks added for legibility).  We can write in Perl
+
+ $var =~ m/mushroom/
+
+The value of this expression will be TRUE if C<$var> contains that
+sequence of characters, and FALSE otherwise.  The portion enclosed in
+C<"E<sol>"> characters denotes the characteristic we are looking for.
+We use the term I<pattern> for it.  The process of looking to see if the
+pattern occurs in the string is called I<matching>, and the C<"=~">
+operator along with the C<"m//"> tell Perl to try to match the pattern
+against the string.  Note that the pattern is also a string, but a very
+special kind of one, as we will see.  Patterns are in common use these
+days;
 examples are the patterns typed into a search engine to find web pages
 and the patterns used to list files in a directory, e.g., C<ls *.txt>
 or C<dir *.*>.  In Perl, the patterns described by regular expressions
-are used to search strings, extract desired parts of strings, and to
-do search and replace operations.
+are used not only to search strings, but to also extract desired parts
+of strings, and to do search and replace operations.
 
 Regular expressions have the undeserved reputation of being abstract
-and difficult to understand.  Regular expressions are constructed using
+and difficult to understand.  This really stems simply because the
+notation used to express them tends to be terse and dense, and not
+because of inherent complexity.  We recommend using the C<"/x"> regular
+expression modifier (described below) along with plenty of white space
+to make them less dense, and easier to read.  Regular expressions are
+constructed using
 simple concepts like conditionals and loops and are no more difficult
 to understand than the corresponding C<if> conditionals and C<while>
-loops in the Perl language itself.  In fact, the main challenge in
-learning regular expressions is just getting used to the terse
-notation used to express these concepts.
+loops in the Perl language itself.
 
 This tutorial flattens the learning curve by discussing regular
 expression concepts, along with their notation, one at a time and with
@@ -58,7 +79,7 @@ find things that, while legal, may not be what you intended.
 =head2 Simple word matching
 
 The simplest regexp is simply a word, or more generally, a string of
-characters.  A regexp consisting of a word matches any string that
+characters.  A regexp consisting of just a word matches any string that
 contains that word:
 
     "Hello World" =~ /World/;  # matches