while($string =~/(simple)/g){ 
my $postition = pos($string);
print "most recent match is $1, at position $position\n";
}
##</code><code>##

#!/usr/bin/perl -w

=begin

running a global match on the same string twice can have side effects.  The pos($testString) or ending position of the last match changes around behind the scenes.  When using the /g modifier in scalar context, the next search will start from the position of the last match, not the beginning of the string each time.  To reset this position and restart from the beginning, you need a failed match or you can reset manually using the pos() function i.e. pos($test3) = 0 restarts matching from the beginning of the string.

Also @- is the builtin array that contains the beginning position of all the matches if you were doing this manually like in a while loop
=end 
=cut

my $test1 = $test2 = $test3 = "This is a simple thing, just a simple simple thing.";
my @matches;
my $position;
print "String: \"$test1\"\n\n";

print "first test scalar context:\n";
$test1 =~ /(simple)/g;
$position = pos($test1);
print "\$1 is $1, pos(\$test1) is $position\n" if($1);
print "\$2 is $2, pos(\$test1) is $position\n" if($2);#no match because scalar context /g only gets the first match
print "\$3 is $3, pos(\$test1) is $position\n" if($3);#no match because (same)
print "\n";

print "second test list context:\n";
@matches = $test2 =~ /(simple)/g;#matches all three in list context, apparently does not set pos.  Cant use foreach loop must use while loop if you needed the positions
my $i = 0;

for (@matches){
    print "Match $i is $_\n";
    $i++;
}
print "\n";



=begin
scalar context /g doesnt go to end of string, it stops at a match...  Next search begins at the position of this match.  To match all the way to end of a string, use list context or scalars in a loop structure.  A loop structure is useful if you needed the position of each match which would be in pos($test3)

#https://www.oreilly.com/library/view/perl-in-a/1565922867/re148.html
=end
=cut
print "third test scalar context but with looping:\n";
$i=0;
while($test3 =~ /(simple)/g){ 
    my $position = pos($test3);

    print "\$1 is $1, pos(\$test3) is $position, loop counter is $i\n" if($1);
    print "\$2 is $2, pos(\$test3) is $position, loop counter is $i\n" if($2);#no match because scalar context
    print "\$3 is $3, pos(\$test3) is $position, loop counter is $i\n" if($3);#no match because scalar context
    #can reset position like this if you needed to pos($test3) = 0;
    $i++;
    if($i > 10){ last;}#watch out for infinite loops too if you reset the position in the while loop
}
    print "\n";

##</code><code>##

$perl simple.pl
String: "This is a simple thing, just a simple simple thing."

first test scalar context:
$1 is simple, pos($test1) is 16

second test list context:
Match 0 is simple
Match 1 is simple
Match 2 is simple

third test scalar context but with looping:
$1 is simple, pos($test3) is 16, loop counter is 0
$1 is simple, pos($test3) is 37, loop counter is 1
$1 is simple, pos($test3) is 44, loop counter is 2