$ perl -MO=Concise,-exec -e'$x = qq{a $b c}'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  <$> const[PV "a "] s
4  <#> gvsv[*b] s
5  <2> concat[t3] sK/2
6  <$> const[PV " c"] s
7  <2> concat[t4] sKS/2
8  <#> gvsv[*x] s
9  <2> sassign vKS/2
a  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'$x = q{a }.$b.q{ c}'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  <$> const[PV "a "] s
4  <#> gvsv[*b] s
5  <2> concat[t3] sK/2
6  <$> const[PV " c"] s
7  <2> concat[t4] sKS/2
8  <#> gvsv[*x] s
9  <2> sassign vKS/2
a  <@> leave[1 ref] vKP/REFC
-e syntax OK