Remove a random expression from string

Question

I have a string/column something like this

String a = \"000003023_AggregateStopLossLimit_W x3A 973911_2012-12-22.PDF\";

I want to create a subs

Answer 1

final String r = a.replaceAll(" .*?(?=_)", "");

if you print the r, it gave output:

000003023_AggregateStopLossLimit_W_2012-12-22.PDF