I think you can use Add_Delta_DHMS adding -1 month (well I intended Add_Delta_YMD )

update

perl -e "use Date::Calc qw(Add_Delta_YMD); ($year, $month, $day) = Add
+_Delta_YMD(2003, 8,1,0,-1,0); print qq($month/$year)"


7/2003
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L*