Something you say isn't true, or your perl is very broken because

while (<DATA>) {
   print $1 if /\bco_java_(\w+\n)/;
}

__DATA__
juserl 8593596 1 0 Oct 15 - 0:43 co_java_for03
juserl 23107 1 0 Oct 15 ? 1:15 co_java_burl9
[download]

outputs

for03
burl9
[download]