R - how can I dump contents of file to console output?

You have to specify a length (which can be too big), but maybe readChar would help:

cat(readChar(filename, 1e5))

You could use system to call a system command.

system("cat yourfile.txt")

Use writeLines instead of print. The default con for writeLines is stdout(), so writeLines(readLines(...)) sounds right.

See ?writeLines.