ref: 3206ebbc2fbd2d489d12a559b5d4e68fdfdc5ffc
dir: /test/t.re4/
BEGIN { r1 = "xxx"
r2 = "xxx" ":"
r3 = ":" r2
r4 = "a"
}
$0 ~ r1 { print $0 " matches " r1 }
$0 ~ r2 { print $0 " matches " r2 }
$0 ~ r3 { print $0 " matches " r3 }
$0 ~ r4 { print $0 " matches " r4 }