Thanks, I'm committing it with this additional rewording..
+While @command{printf} is not available on all systems, it is safer and
+easier to use than @command{echo}.
+Thus, new applications which are not aiming at portability should use
+...@command{printf} instead of @command{echo}.
+When portability is important, M4sh provides the @code{AS_ECHO} and
+...@code{as_echo_n} macros, which choose between @samp{echo -n} on
+implementations where that works, @command{printf} if it is available,
+or other creative tricks in order to work around the above problems.
While @command{printf} is not a builtin on all systems, it is safer and
easier to use than @command{echo}. Thus, scripts where portability is
not a major concern should use @command{printf '%s\n'} instead of
@command{echo}, and @command{printf %s} instead of @command{echo -n}.
For portable shell scripts it is suggested to use M4sh and its
@code{AS_ECHO} and @code{AS_ECHO_N} macros, which choose between various
implementations: @samp{echo} or @samp{print} where that works,
@command{printf} if it is available, or other creative tricks in order
to work around the above problems.
> +...@command{printf} is not available on all systems.
@command{printf} is not always a builtin; if not, every invocation would
cause a fork and the consequent speed penalty.
