If I understand what you try to do here, just use paste
or paste0
:
stock.name <- "GOOG.O"
FRIDAY <- read.delim(header=TRUE, stringsAsFactor=FALSE,
paste0("http://hopey.netfonds.no/tradedump.php?date=", Friday,
"&paper=", stock.name,
"&csv_format=txt")
)