Discussed starting at
<http://lists.gnu.org/archive/html/bug-autoconf/2009-07/msg00025.html>.
* doc/autoconf.texi (Limitations of Builtins): In echo's entry,
give a reason why printf is better than echo. In printf's
entry, cross-reference echo's entry.
---
Here is what I committed.
ChangeLog | 8 ++++++++
doc/autoconf.texi | 28 ++++++++++++++++++----------
2 files changed, 26 insertions(+), 10 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 9011143..1e22e63 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2009-07-30 Paolo Bonzini <bonz...@gnu.org>
+ Joel E. Denny <jde...@clemson.edu>
+
+ Clarify comparison of echo, printf, and AS_ECHO*.
+ * doc/autoconf.texi (Limitations of Builtins): In echo's entry,
+ give a reason why printf is better than echo. In printf's
+ entry, cross-reference echo's entry.
+
2009-07-26 Eric Blake <e...@byu.net>
Release Version 2.64.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 4f046c0..419d7cd 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15826,9 +15826,14 @@ Limitations of Builtins
Because of these problems, do not pass a string containing arbitrary
characters to @command{echo}. For example, @samp{echo "$foo"} is safe
-if you know that @var{foo}'s value cannot contain backslashes and cannot
-start with @samp{-}, but otherwise you should use a here-document like
-this:
+only if you know that @var{foo}'s value cannot contain backslashes and
+cannot start with @samp{-}.
+
+...@command{printf} is in general safer and easier to use than @command{echo}
+and @command{echo -n}. 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 a here-document like this:
@example
cat <<EOF
@@ -15836,12 +15841,12 @@ Limitations of Builtins
EOF
@end example
-New applications which are not aiming at portability should use
-...@command{printf} instead of @command{echo}. 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.
+...@noindent
+in cases that could trigger bugs in @command{echo}. Alternatively,
+M4sh provides @code{AS_ECHO} and @code{AS_ECHO_N} macros which choose
+between various portable 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.
@item @command{eval}
@@ -16143,11 +16148,14 @@ Limitations of Builtins
core.
Since @command{printf} is not always a shell builtin, there is a
-potential speed penalty for using @code{printf %s\\n} as a replacement
+potential speed penalty for using @code{printf '%s\n'} as a replacement
for an @command{echo} that does not interpret @samp{\} or leading
@samp{-}. With Solaris @command{ksh}, it is possible to use @code{print
-r --} for this role instead.
+For a discussion of portable alternatives to both @command{printf}
+and @command{echo}, @xref{echo, , Limitations of Shell Builtins}.
+
@item @command{pwd}
@c ----------------
--
1.6.2.5
