write-line

(write-line string &optional stream)

Writes the given string followed by a newline, and returns the string. With no stream argument it writes to standard output; given an output stream it writes there instead -- a file stream opened by open or with-open-file, a socket, or a with-output-to-string string stream. Works in all three backends. Unlike print/prin1, it writes the raw string contents without surrounding quotes.

(with-open-file (out "greeting.txt" :direction :output)
  (write-line "hello" out)
  (write-line "world" out))

This writes two lines, hello and world, into greeting.txt. Each call appends its own trailing newline and returns the string it wrote.