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>perl -wE "say for unpack '(CX/xX.@0x/A)*', qq(\03ab\05cdef\06ghijk)" ab ... 67 Hello!
>perl -wE "say for unpack '(C/xX2.@0x/A)(CX2/x.@0x/A)*', qq(\03ab\05cd +ef\06ghijk)" ab ... 67 Hello!