# HG changeset patch
# User Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
# Date 1295711092 -3600
# Node ID f2c6946affe2df591ee04c3a1c584a2b5bdc068f
# Parent  983668dc6e168021fcc324e6e4f28622b2fed44d
move-if-change: cope with concurrent mv of identical file.

* build-aux/move-if-change (CMPPROG): Accept environment
variable as an override for `cmp'.
(usage): Document CMPPROG.
Adjust comparison to drop stdout.  Cope with failure of mv if
the target file exists and is identical to the source, for
parallel builds.
Report from H.J. Lu against binutils in PR binutils/12283.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>

diff --git a/ChangeLog b/ChangeLog
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2011-01-28  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
+
+	move-if-change: cope with concurrent mv of identical file.
+	* build-aux/move-if-change (CMPPROG): Accept environment
+	variable as an override for `cmp'.
+	(usage): Document CMPPROG.
+	Adjust comparison to drop stdout.  Cope with failure of mv if
+	the target file exists and is identical to the source, for
+	parallel builds.
+	Report from H.J. Lu against binutils in PR binutils/12283.
+
 2011-01-28  Bruce Korb  <bkorb@gnu.org>
 
 	* users.txt: Mention sharutils.
diff --git a/build-aux/move-if-change b/build-aux/move-if-change
--- a/build-aux/move-if-change
+++ b/build-aux/move-if-change
@@ -2,7 +2,7 @@
 # Like mv $1 $2, but if the files are the same, just delete $1.
 # Status is zero if successful, nonzero otherwise.
 
-VERSION='2007-09-28 23:10'; # UTC
+VERSION='2011-01-28 20:09'; # UTC
 # The definition above must lie within the first 8 lines in order
 # for the Emacs time-stamp write hook (at end) to update it.
 # If you change this file with Emacs, please let the write hook
@@ -32,15 +32,18 @@
   --help     display this help and exit
   --version  output version information and exit
 
+The variable CMPPROG can be used to specify an alternative to \`cmp'.
+
 Report bugs to <bug-gnulib@gnu.org>."
 
 version=`expr "$VERSION" : '\([^ ]*\)'`
 version="move-if-change (gnulib) $version
-Copyright (C) 2007 Free Software Foundation, Inc.
+Copyright (C) 2011 Free Software Foundation, Inc.
 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law."
 
+cmpprog=${CMPPROG-cmp}
 
 for arg
 do
@@ -60,12 +63,15 @@
   esac
 done
 
-test $# = 2 || { echo "$0: $usage" >&2; exit 1; }
+test $# -eq 2 || { echo "$0: $usage" >&2; exit 1; }
 
-if test -r "$2" && cmp -s -- "$1" "$2"; then
+if test -r "$2" && $cmpprog -- "$1" "$2" >/dev/null; then
   rm -f -- "$1"
 else
-  mv -f -- "$1" "$2"
+  if mv -f -- "$1" "$2"; then :; else
+    # Ignore failure due to a concurrent move-if-change.
+    test -r "$2" && $cmpprog -- "$1" "$2" >/dev/null && rm -f -- "$1"
+  fi
 fi
 
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