Re: 21doc-cp-r-portability.diff

[Paul Eggert]

Alexandre Duret-Lutz <address@hidden> writes:

> This minus `-r' just caught my eye.  
> What should be preferred between `cp -R' and `cp -r'?

-R.

> Automake's lib/am/distdir.am uses `cp -R' and claims `cp -r' to
> be "almost always incorrect".

-R's behavior is defined by POSIX.  -r's is not.  With GNU cp, there's
no difference.  With Solaris cp, -r reads from pipes instead of
replicating them, which is typically not what you want.  For example:

$ mkdir d
$ cd d
$ ls
$ mkdir d
$ mkfifo d/fifo
$ (sleep 10; echo foo >d/fifo)& date; cp -r d e; date
[1] 2400
Wed Nov 10 16:04:31 PST 2004
Wed Nov 10 16:04:41 PST 2004
[1]+  Done                    ( sleep 10; echo foo >d/fifo )
$ ls -l d e
d:
total 0
prw-rw-r--   1 eggert   eggert         0 Nov 10 16:04 fifo

e:
total 16
-rw-rw-r--   1 eggert   eggert         4 Nov 10 16:04 fifo


Thanks for catching this.  I installed the following patch:

2004-11-10  Paul Eggert  <address@hidden>

        * doc/autoconf.texi (Limitations of Usual Tools): Avoid cp -r;
        use cp -R instead.

--- autoconf.texi.~1.838.~      2004-11-10 13:51:48 -0800
+++ autoconf.texi       2004-11-10 16:08:43 -0800
@@ -11223,10 +11223,15 @@ newline encoding.
 @item @command{cp}
 @c ---------------
 @prindex @command{cp}
+Avoid the @option{-r} option, since its behavior is not specified by
+Posix.  Use @option{-R} instead.  On @acronym{GNU} hosts the two options
+are equivalent, but on Solaris 9 hosts (for example) @command{cp -r}
+reads from pipes instead of replicating them.
+
 Some @command{cp} implementations (e.g., BSD/OS 4.2) do not allow
 trailing slashes at the end of nonexistent destination directories.  To
 avoid this problem, omit the trailing slashes.  For example, use
address@hidden -r source /tmp/newdir} rather than @samp{cp -r source
address@hidden -R source /tmp/newdir} rather than @samp{cp -R source
 /tmp/newdir/} if @file{/tmp/newdir} does not exist.
 
 @c This is thanks to Ian.