Programming Perl, 4th Edition

index

index STR, SUBSTR, OFFSET
index STR, SUBSTR

This function searches for one literal string within another. It returns the position of the first occurrence of SUBSTR in STR. The OFFSET, if specified, says how many characters from the start to skip before beginning to look. Positions are based at 0. If the substring is not found, the function returns one less than the base, ordinarily –1. To work your way through a string, you might say:

$pos = –1;
while (($pos = index($string, $lookfor, $pos)) > –1) {
    say "Found at $pos"; $pos++;
}

Offsets are always by programmer-visible characters (i.e., codepoints), not by user-visible characters (graphemes). The offset is in bytes only if you have already decoded from abstract characters into some serialization scheme, like UTF-8 or UTF-16. See Chapter 6.

To work with strings as sequences of graphemes instead of codepoints, see the index, rindex, and pos methods for the CPAN Unicode::GCString module.