[Unison-hackers] Re: Bug in / patch for Unison 2.12.0's Makefile.OCaml

[Zvezdan Petkovic]

On Mon, Jun 20, 2005 at 10:46:14PM -0400, Benjamin Pierce wrote:
> Thanks for the suggestion, Nick.  I've made this change in the source.  
> (If someone can try it out on Windows, that would be great.)

You might want to retract a part of it. :-)

> >
> > The literal control-M can be represented by "\r".
> >

WRONG!
According to POSIX sed uses _basic_ regular expressions.
OTOH, awk and egrep use _extended_ REs. 

> >This seems to work for me on Ubuntu 5.04 and Solaris as well as OS X 
> >10.4:

Are you sure about Solaris?

> >
> >OCAMLLIBDIR=$(shell ocamlc -v | sed -n '$p' | sed -e 's/^Standard 
> >library directory: //' | sed -e 's/\\/\//g' | sed -e 's/\r//g')

This last part doesn't work in most POSIXly correct sed implementations.
I just tested it on OpenBSD, HP-UX, _and_ Solaris.

The file is:
aaa
a^Mb
bbb

Now,
$ cat t
aaa
b
bbb

You can't see a in the second line because ^M returns to the beginning
of the line and prints b over it.  Lets test how sed works:

$ cat t | sed 's/\r//g'
aaa
b
bbb

No change when I redirect the output into the file.
The ^M is still there.

Now, using Ctrl-V Ctrl-M to type ^M I get.

$ cat t | sed 's/^M//g'
aaa
ab
bbb

Now it works.
And that is the only way it will work on OpenBSD, HP-UX _and_ Solaris.

Here's a fingerprint of all machines I ran it on without success when \r
is used.

$ uname -rs
OpenBSD 3.7

$ uname -rs
HP-UX B.11.11

$ uname -rs
SunOS 5.9

The only machine where it succeeded for me is:

$ uname -rs
Linux 2.6.5-7.155.29-smp

> >
> >I haven't tested it on Windows.
> >

Considering that Microsoft Services for UNIX return

	OpenBSD

when you type

	string /usr/bin/* | grep BSD

and it seems some very old rip-off version, I'll bet it will work the
same on Windows on my office machine.
Now, Cygwin could be a different beast being based on Linux.

The bottom line is that \r in sed is _not_ portable.
Keep ^M there.
There's a good reason it was there for so long time.

Welcome to the friendly world of UNIX portability.
:-)

	Zvezdan Petkovic