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
index 749be54..a6f5f35 100644 (file)
--- 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
index a891ca5..e7ba25e 100755 (executable)
--- 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 @@ If SOURCE is different than DEST, then move it to DEST; else remove SOURCE.
   --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 @@ do
   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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