>perl -MO=Concise -e"substr($x,0,1)=''"
9  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
8     <2> sassign vKS/2 ->9                  <---
3        <$> const[PV ""] s ->4
7        <@> substr[t3] sKRM*/3 ->8          <---
-           <0> ex-pushmark s ->4
-           <1> ex-rv2sv sKRM*/1 ->5
4              <#> gvsv[*x] s ->5
5           <$> const[IV 0] s ->6
6           <$> const[IV 1] s ->7
-e syntax OK