From: Eric Blake <ebb9@byu.net>
Date: Thu, 13 Sep 2007 16:50:38 +0000 (+0000)
Subject: Document another awk pitfall.
X-Git-Tag: v2.62~270
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=097669a284f818a4f8fb9f094df478a9e226f266;p=thirdparty%2Fautoconf.git

Document another awk pitfall.
* doc/autoconf.texi (Limitations of Usual Tools) <awk>: Document
limitation of field variables in END.
Reported by Gary V. Vaughan.
---

diff --git a/ChangeLog b/ChangeLog
index c49031cd..d0ce0a6e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2007-09-13  Eric Blake  <ebb9@byu.net>
 
+	Document another awk pitfall.
+	* doc/autoconf.texi (Limitations of Usual Tools) <awk>: Document
+	limitation of field variables in END.
+	Reported by Gary V. Vaughan.
+
 	* AUTHORS: Add missing entries.
 
 2007-09-12  Eric Blake  <ebb9@byu.net>
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 52faf505..e5d2fee1 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -13361,6 +13361,23 @@ input in this case.  Portable scripts can redirect input from
 awk 'BEGIN @{print "hello world"@}' </dev/null
 @end example
 
+Posix says that in an @samp{END} action, @samp{$NF} (and presumably,
+@samp{$1}) retain their value from the last record read, if no
+intervening @samp{getline} occurred.  However, some implementations
+(such as Solaris 10 @samp{/usr/bin/awk}, @samp{nawk}, or Darwin
+@samp{awk}) reset these variables.  A workaround is to use an
+intermediate variable prior to the @samp{END} block.  For example:
+
+@example
+$ @kbd{cat end.awk}
+@{ tmp = $1 @}
+END @{ print "a", $1, $NF, "b", tmp @}
+$ @kbd{echo 1 | awk -f end.awk}
+a   b 1
+$ @kbd{echo 1 | gawk -f end.awk}
+a 1 1 b 1
+@end example
+
 If you want your program to be deterministic, don't depend on @code{for}
 on arrays: