the.string <- "ABCDE982y987r0jhABCdioy2093uiwhf"
the.substrings <- c("ABC", "DEF", "GHI", "987", "ABCDE")
regmatches(the.string, gregexpr(paste(the.substrings, collapse="|"), the.string))
dGhlLnN0cmluZyA8LSAiQUJDREU5ODJ5OTg3cjBqaEFCQ2Rpb3kyMDkzdWl3aGYiCnRoZS5zdWJzdHJpbmdzIDwtIGMoIkFCQyIsICJERUYiLCAiR0hJIiwgIjk4NyIsICJBQkNERSIpCnJlZ21hdGNoZXModGhlLnN0cmluZywgZ3JlZ2V4cHIocGFzdGUodGhlLnN1YnN0cmluZ3MsIGNvbGxhcHNlPSJ8IiksIHRoZS5zdHJpbmcpKQ==