#START is the pattern you want to grep at the BEGINNING of a string
#END is the pattern you want to grep at the END of a string
#Grep string that start with START and end with END (both grep have to occur)
grep("^START.*\\.END$", filenames, ignore.case = T)
#Grep a string that starts with START
grep("^START", filenames)
#Grep a string that ends with END
gerep("END$", filenames)