http://www.perlmonks.org?node_id=1073236


in reply to Re^2: avoid writing 'use utf8' in every script
in thread avoid writing 'use utf8' in every script

use utf8; does not use result in any code.

>perl -MO=Concise,-exec -e"use utf8; $x='abc';" 1 <0> enter 2 <;> nextstate(main 7 -e:1) v:U,{ 3 <$> const[PV "abc"] s 4 <#> gvsv[*x] s 5 <2> sassign vKS/2 6 <@> leave[1 ref] vKP/REFC -e syntax OK

It has a compile-time effect.