$ perl -e'
   use feature qw( say );
   $! = 2;
   say 0+\$!;
   say 0+$!;
   sub {
      local $! = 3;
      say 0+\$!;
      say 0+$!;
      say 0+$_[0];
   }->( $! );
   say 0+\$!;
   say 0+$!;
'
93839899443048   Address of pre-local $!
2                Value of pre-local $! (aka value of errno)
93839899247848   Address of post-local $!
3                Value of post-local $! (aka value of errno)
3                Value of pre-local $! (aka value of errno)
93839899443048   $! is restored
3                Value of pre-local $! (aka value of errno)