set str {Pattern[1]:
Key : "key1"
Value : 100
Pattern[2]:
Key : "key2"
Value : 20
Pattern[3]:
Key : "key3" Value : 30
Pattern[4]:
Key : "key4"
Value : 220"}
set updateList [regexp -all -inline {Pattern\[\d+\]:\s*Key[^\n]*\s*Value[^\n]*} $str]
puts $updateList
c2V0IHN0ciB7UGF0dGVyblsxXTogCktleSA6ICJrZXkxIiAKVmFsdWUgOiAxMDAKUGF0dGVyblsyXTogCktleSA6ICJrZXkyIiAKVmFsdWUgOiAyMApQYXR0ZXJuWzNdOiAKS2V5IDogImtleTMiIFZhbHVlIDogMzAKUGF0dGVybls0XTogCktleSA6ICJrZXk0IiAKVmFsdWUgOiAyMjAifQoKc2V0IHVwZGF0ZUxpc3QgW3JlZ2V4cCAtYWxsIC1pbmxpbmUge1BhdHRlcm5cW1xkK1xdOlxzKktleVteXG5dKlxzKlZhbHVlW15cbl0qfSAkc3RyXQpwdXRzICR1cGRhdGVMaXN0