Programming Perl, 4th Edition

pos

pos SCALAR
pos

This function returns the location in SCALAR where the last m//g search over SCALAR left off.

It returns the offset of the character (codepoint) after the last one matched. (That is, it’s equivalent to length($`) + length($&).) This is the offset where the next m//g search on that string will start. Remember that the offset of the beginning of the string is 0. Note that 0 is a valid match offset. undef indicates that the search position is reset (usually due to match failure, but it can also be because no match has been run on the scalar yet).

For example:

$graffito = "fee fie foe foo";
while ($graffito =~ m/e/g) {
    say pos $graffito;
}

prints 2, 3, 7, and 11, the offsets of each of the codepoints following an “e”. The pos function may be assigned a value to tell the next m//g where to start:

$graffito = "fee fie foe foo";
pos $graffito = 4;  # Skip the fee, start at fie
while ($graffito =~ m/e/g) {
    say pos $graffito;
}

This prints only 7 and 11. The regular expression assertion \G matches only at the location currently specified by pos for the string being searched. See the section Positions in Chapter 5.

Note that we said codepoints, not characters. We didn’t want to confuse you. Codepoints are programmer-visible characters, some of which may even be invisible to users. A user-visible character, usually called graphemes or grapheme clusters, may well comprise multiple ...