Printing newlines with print() in R

Question

An alternative to cat() is writeLines():

> writeLines("File not supplied.\nUsage: ./program F=filename")
File not supplied.
Usage: ./program F=filename
>

An advantage is that you don't have to remember to append a "\n" to the string passed to cat() to get a newline after your message. E.g. compare the above to the same cat() output:

> cat("File not supplied.\nUsage: ./program F=filename")
File not supplied.
Usage: ./program F=filename>

and

> cat("File not supplied.\nUsage: ./program F=filename","\n")
File not supplied.
Usage: ./program F=filename
>

The reason print() doesn't do what you want is that print() shows you a version of the object from the R level - in this case it is a character string. You need to use other functions like cat() and writeLines() to display the string. I say "a version" because precision may be reduced in printed numerics, and the printed object may be augmented with extra information, for example.

You can do this:

cat("File not supplied.\nUsage: ./program F=filename\n")

Notice that cat has a return value of NULL.

Using writeLines also allows you to dispense with the "\n" newline character, by using c(). As in:

writeLines(c("File not supplied.","Usage: ./program F=filename",[additional text for third line]))

This is helpful if you plan on writing a multiline message with combined fixed and variable input, such as the [additional text for third line] above.

You can also use a combination of cat and paste0

cat(paste0("File not supplied.\n", "Usage: ./program F=filename"))

I find this to be more useful when incorporating variables into the printout. For example:

file <- "myfile.txt"
cat(paste0("File not supplied.\n", "Usage: ./program F=", file))