perl -Mre=debug -e '@rr = "efgmnoxyz" =~ /(?=(\w\w\w))/g'

##</code><code>##

# perl -Mre=debug -e '@matches = "efgmnoxyz" =~ /(\w\w\w)/g' 2>&1 | grep 'Matching REx'
Matching REx "(\w\w\w)" against "efgmnoxyz"
Matching REx "(\w\w\w)" against "mnoxyz"
Matching REx "(\w\w\w)" against "xyz"

##</code><code>##

# perl -Mre=debug -e '@matches = "efgmnoxyz" =~ /(?=(\w\w\w))/g' 2>&1 | grep 'Matching REx'
Matching REx "(?=(\w\w\w))" against "efgmnoxyz"
Matching REx "(?=(\w\w\w))" against "efgmnoxyz"
Matching REx "(?=(\w\w\w))" against "fgmnoxyz"
Matching REx "(?=(\w\w\w))" against "gmnoxyz"
Matching REx "(?=(\w\w\w))" against "mnoxyz"
Matching REx "(?=(\w\w\w))" against "noxyz"
Matching REx "(?=(\w\w\w))" against "oxyz"
Matching REx "(?=(\w\w\w))" against "xyz"