Learning Perl, 7th Edition

Chapter 14. Strings and Sorting

As we mentioned near the beginning of this book, Perl is designed to be good at solving programming problems that are about 90% working with text and 10% everything else. So it’s no surprise that Perl has strong text-processing abilities, even without all that you’ve done with regular expressions. Sometimes the regular expression engine is too fancy and you need a simpler way of working with a string, as you’ll see in this chapter.

Finding a Substring with index

Finding a substring depends on where you lost it. If you happen to have lost it within a bigger string, you’re in luck because the index function can help you out. Here’s how it looks:

my $where = index($big, $small);

Perl locates the first occurrence of the small string within the big string, returning an integer location of the first character. The character position returned is a zero-based value—if the substring is found at the very beginning of the string, index returns 0. If it’s one character later, the return value is 1, and so on. If index can’t find the substring at all, it returns -1 to indicate that. In this example, $where gets 6 because that’s the position where wor starts:

my $stuff = "Howdy world!";
my $where = index($stuff, "wor");

Another way you could think of the position number is the number of characters to skip over before getting to the substring. Since $where is 6, you know that you have to skip over the first six characters of $stuff before you find wor.

The index function ...