6.14.1. Problem

6.14.3. Discussion

while (/(\d+)/g) {
    print "Found number $1\n";
}

Within a pattern, \G means the end of the previous match. For example, if you had a number stored in a string with leading blanks, you could change each leading blank into the digit zero this way:

$n = "   49 here";
$n =~ s/\G /0/g;
print $n;
00049 here

while (/\G,?(\d+)/g) {
    print "Found number $1\n";
}

By default, when your match fails (when we run out of numbers in the examples, for instance) the remembered position is reset to the start. If you don't want this to happen, perhaps because you want to continue matching from that position but with a different pattern, use the modifier /c with /g:

$_ = "The year 1752 lost 10 days on the 3rd of September";

while (/(\d+)/gc) {
    print "Found number $1\n";
}
# the /c above left pos at end of final match

if (/\G(\S+)/g) {
    print "Found $1 right after the last number.\n";
}

Found number 1752
Found number 10
Found number 3
Found rd after the last number.

Successive patterns can use /g on a string, which remembers the ending position of the last successful match. That position is associated with the scalar matched against, not with the pattern. It's reset if the string is modified.

$a = "Didst thou think that the eyes of the White Tower were blind?";
$a =~ /(\w{5,})/g;
print "Got $1, position in \$a is ", pos($a), "\n";
Got Didst, position in $a is 5

pos($a) = 30;
$a =~ /(\w{5,})/g;
print "Got $1, position in \$a now ", pos($a), "\n";
Got White, position in $a now 43

Without an argument, pos operates on $_:

$_ = "Nay, I have seen more than thou knowest, Grey Fool.";
/(\w{5,})/g;
print "Got $1, position in \$_ is ", pos, "\n";
pos = 42;
/\b(\w+)/g;
print "Next full word after position 42 is $1\n";

Got knowest, position in $_ is 39
Next full word after position 42 is Fool