my_string = "esrhjg erguhg rziughrtPARTITIONED BY hzueirghf zreeuifh iuehg reuhg riutghSTORED ASiugh oer hfz"
sub( "PARTITIONED BY.*STORED AS" , "PARTITIONED BY -TO_REPLACE- STORED AS" , my_string)
## or with backreferences:
sub( "(PARTITIONED BY).*(STORED AS)" , "\\ 1 -TO_REPLACE- \\ 2" , my_string)
bXlfc3RyaW5nID0gImVzcmhqZyBlcmd1aGcgcnppdWdocnRQQVJUSVRJT05FRCBCWSBoenVlaXJnaGYgenJlZXVpZmggaXVlaGcgcmV1aGcgcml1dGdoU1RPUkVEIEFTaXVnaCBvZXIgaGZ6IgpzdWIoIlBBUlRJVElPTkVEIEJZLipTVE9SRUQgQVMiLCAiUEFSVElUSU9ORUQgQlkgLVRPX1JFUExBQ0UtIFNUT1JFRCBBUyIsIG15X3N0cmluZykKIyMgb3Igd2l0aCBiYWNrcmVmZXJlbmNlczoKc3ViKCIoUEFSVElUSU9ORUQgQlkpLiooU1RPUkVEIEFTKSIsICJcXDEgLVRPX1JFUExBQ0UtIFxcMiIsIG15X3N0cmluZyk=