ifchange: no overwrite with an empty file

* tool/ifchange, win32/ifchange.bat: do not overwrite with an empty
  file by default, and add --empty option to force it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43519 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 5 insertions, 1 deletions

diff --git a/tool/ifchange b/tool/ifchange
index 5695e5a9b8..488e9db26e 100755
--- a/tool/ifchange
+++ b/tool/ifchange
@@ -4,6 +4,7 @@
 set -e
 timestamp=
 keepsuffix=
+empty=
 until [ $# -eq 0 ]; do
     case "$1" in
 	--timestamp)
@@ -18,6 +19,9 @@ until [ $# -eq 0 ]; do
 	--keep=*)
 	    keepsuffix=`expr \( "$1" : '[^=]*=\(.*\)' \)`
 	    ;;
+	--empty)
+	    empty=yes
+	    ;;
 	*)
 	    break
 	    ;;
@@ -33,7 +37,7 @@ if [ "$temp" = - ]; then
     trap 'rm -f "$temp"' 0
 fi
 
-if cmp "$target" "$temp" >/dev/null 2>&1; then
+if [ -f "$target" -a ! -${empty:+f}${empty:-s} "$temp" ] || cmp "$target" "$temp" >/dev/null 2>&1; then
     echo "$target unchanged"
     rm -f "$temp"
 else