[PATCH] Add recommendation on (not) unsetting IFS.

[Paolo Bonzini]

What about this change?  It was discussed yesterday on the qemu
mailing list, and one developer referred to the Autoconf manual
even though qemu does not use Autoconf.

* doc/autoconf.texi (Special shell variables): Explain why it's
better not to unset IFS.
---
 ChangeLog         |    6 ++++++
 doc/autoconf.texi |   16 ++++++++++++++++
 2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index eaee96b..70432f8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2010-01-20  Paolo Bonzini  <address@hidden>
+
+       Add recommendation on (not) unsetting IFS.
+       * doc/autoconf.texi (Special shell variables): Explain why it's
+       better not to unset IFS.
+
 2010-01-19  Ralf Wildenhues  <address@hidden>
 
        config.status: consistent exit status with nonexistent config file 
input.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 1549f89..e5cf9fd 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15750,6 +15750,22 @@ Special Shell Variables
 @file{configure} scripts and M4sh do that for you.
 Export these variables after setting them.
 
+Unsetting @code{IFS} instead of resetting it to the default sequence
+is not suggested, since code that tries to save and restore the
+variable's value will incorrectly reset it to an empty value, thus
+disabling field splitting:
+
address@hidden
+unset IFS
+# default separators used for field splitting
+
+save_IFS=$IFS
+IFS=:
+# ...
+IFS=$save_IFS
+# no field splitting performed
address@hidden example
+
 @c  However, some older, nonstandard
 @c  systems (notably @acronym{SCO}) break if locale environment variables
 @c  are set to @samp{C}, so when running on these systems
-- 
1.6.5.2