#!/usr/bin/perl

# Working with Strings and Substrings 

#  Using "length" to find the length of a string

$sentence = "Perl is great at manipulating strings, naturally.";
$len = length $sentence;
print "$sentence \n";
print "This string is $len characters long.\n\n";


# Using "index" to find a substring  which returns the position
#  of some substring, or -1 if it is not found there.  

# Command Format:  $x = index ($bigstring, $littlestring);


$word = "Perl";
$where = index( $sentence, $word);
print "$sentence \n";
print "$word begins at character $where \n\n"; 

$word = "great";
$where = index( $sentence, $word);
print "$sentence \n";
print "$word begins at character $where \n\n"; 

$word = "xxx";
$where = index( $sentence, $word);
print "$sentence \n";
print "$word begins at character $where \n\n"; 


# Using "rindex" to find rightmost index

$word = "ing";

$where = index( $sentence, $word);
print "$sentence \n";
print "The first $word begins at character $where \n"; 

$where = rindex( $sentence, $word);
print "The last $word begins at character $where \n\n"; 

# Using the optional third parameter to "index" 
# Commmand Format:   $x = index($bigstring, $littlestring, $skip);
# Commmand Format:   $x = rindex($bigstring, $littlestring, $before);

$word = "at";
$first = index($sentence, $word);
$last = rindex($sentence, $word);
print "$sentence \n";
print "The index of the first $word is $first and the final index is $last\n";
$next = index( $sentence, $word, $first+1);
print "After $first characters, the index of the next $word is $next \n"; 
$previous = rindex( $sentence, $word, $last-1);
print "After $last characters, the index of the previous $word is $previous \n\n"; 

# Extracting and Replacing Substrings
# Command Format:  $s = substr( $string, $start, $length);

# This grabs a substring

$grab = substr( $sentence, 5, 8);
print "$sentence \n";
print "Grabbed Pattern: $grab starts at 5 and goes 8 chars \n\n";

# This replaces a substring
$replacement = "is totally awesome";
substr($sentence, 5, 8) = $replacement;
print "Substituting $replacement staring at 5 and going 8 chars \n"; 
print "$sentence \n\n";