$s = 'abc' x 10; ## repetative test data
$p = 0;          ## start at offset 0

## match against the substring starting at the offset
## and capture (3) items
while( my @x = substr( $s, $p ) =~ m[(.)(.)(.)] ) { 
    print "@x"; ## do something with the captures

    ## and advance the offset to the end of what was matched
    $p += $+[3]; 
}

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