Re: gnulib-tool nits

[Bruno Haible]

Hi Ralf.

> This isn't reliable either: bash 3.1.17 and ksh do this:
> $ ( d=:a:b:; IFS=:; for i in $d ; do echo .$i. ; done )
> ..
> .a.
> .b.
> 
> but pdksh does this:
> $ ( d=:a:b:; IFS=:; for i in $d ; do echo .$i. ; done )
> ..
> .a.
> .b.
> ..

This is only the tip of the iceberg. I tested also the behaviour of empty
fields in the middle (e.g. PATH=/usr/local/bin::/usr/bin:/usr/bin).

The test is this:
   /bin/sh -c 'd=:a:b::c:; IFS=:; for i in $d ; do echo .$i. ; done'

I got four different results:

Result A:
.a.
.b.
.c.

Result B:
.a.
.b.
..
.c.

Result C:
..
.a.
.b.
..
.c.

Result D:
..
.a.
.b.
..
.c.
..

And here's the matrix:

                    /bin/sh  /bin/ksh
                             /usr/xpg4/bin/sh

AIX 5.1                C        C
HP-UX 11               C        C
IRIX 6.5               B        B
OSF/1 4.0, 5.1         A        B
Solaris 7, 10          A        C
FreeBSD 6              D
MacOS X 10.3 (bash)    C
bash 1.14.7            C
bash 2.02.1-2.05       C
bash 3.0-3.2           C
zsh 4.1.1              D

> I think SUSv3 wording is saying that pdksh is right and bash is wrong.  :-/

I cannot find any specification of it at all in POSIX: The relevant text at
  
http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_05
says (for the case IFS=:):

  "the shell shall scan ... for field splitting and multiple fields can result.

   The shell shall treat each character of the IFS as a delimiter and use the
   delimiters to split ... into fields.

   Each occurrence in the input of ':' ... shall delimit a field ..."

It is not clear whether empty fields can occur at all, and under which
conditions they appear at the front or at the end of the result.
  
http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap03.html#tag_03_161
is silent about it.


So, it seems, in order to get portable behaviour, you need to avoid empty
fields:
  pathx=`echo ":$PATH:" | sed -e 's/:::*/:.:/g'`
But then use IFS (so that PATH elements containing spaces are handled
correctly), ignoring empty fields from the cases C and D. In summary,
something like this:

  pathx=`echo ":$PATH:" | sed -e 's/:::*/:.:/g' -e 's/^://' -e 's/:\$//'`
  save_IFS=$IFS
  IFS=:
  for d in $pathx; do
    IFS=$save_IFS
    ...
  done
  IFS=$save_IFS

Bruno