Learning Perl, Fourth Edition

Chapter 13. Strings and Sorting

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, including all that we’ve done with regular expressions. But 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 have 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:

    $where = index($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 beginning of the string, index returns 0. If it’s one character later, the return value is 1, and so on. If the substring can’t be found at all, the return value is -1.^[296] In this example, $where gets 6:

    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, we know we have to skip over the first six characters of $stuff before we find wor.

The index function always reports the location of the first found occurrence of the substring. But you can tell it to start ...