a related question--how do people generally build up decorated strerror messages? e.g. in some versions of ls, "ls foo" (when foo doesn't exist) will print "ls:

a related question--how do people generally build up decorated strerror messages? e.g. in some versions of ls, "ls foo" (when foo doesn't exist) will print "ls: stat: foo: No such file or directory". how is that string built up?