And the reason is that 5.10 doesn't consider "_" in "-X _" a function call. 
>perl588\bin\perl -MO=Concise -e"sub _; -l _"
7  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
6     <1> ftlink vK/1 ->7
5        <1> entersub[t2] sKS/TARG,1 ->6
-           <1> ex-list sK ->5
3              <0> pushmark s ->4
-              <1> ex-rv2cv sK/128 ->-
4                 <#> gv[*_] s ->5
-e syntax OK

>perl589\bin\perl -MO=Concise -e"sub _; -l _"
7  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
6     <1> ftlink vK/1 ->7
5        <1> entersub[t2] sKS/TARG,1 ->6
-           <1> ex-list sK ->5
3              <0> pushmark s ->4
-              <1> ex-rv2cv sK/128 ->-
4                 <#> gv[*_] s ->5
-e syntax OK

>perl5100\bin\perl -MO=Concise -e"sub _; -l _"
4  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v:{ ->3
3     <#> ftlink[*_] vR ->4
-e syntax OK

[download]

In reply to Re^2: Restoring the magic to the _ filehandle in Perl 5.8.9 by ikegami
in thread Restoring the magic to the _ filehandle in Perl 5.8.9 by clinton

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