DB<1> $data = 'key1=val val key2=val key3=val val val val key4=val val'

  DB<2> %hash = $data =~ /([^ =]+)=([^ =]+(?: [^ =]+(?= |$))*)/g

  DB<3> x %hash
0  'key1'
1  'val val'
2  'key2'
3  'val'
4  'key3'
5  'val val val val'
6  'key4'
7  'val val'