add a tool to identify the revision of current work tree or index by content

diff --git a/git-identify-revision b/git-identify-revision
new file mode 100755 (executable)
index 0000000..64e9495
--- /dev/null
+++ b/git-identify-revision
@@ -0,0 +1,47 @@
+#!/bin/sh
+
+# situation: work tree is unknown rev
+# arguments: git rev-list arguments
+# we now identify the one revision with least differences
+
+case "$1" in
+       --cached)
+               use_worktree=false
+               shift
+               ;;
+       *)
+               use_worktree=true
+               ;;
+esac
+
+diffopts="-M -C"
+
+if $use_worktree; then
+       echo >&2 "Saving index..."
+       oldindex=`git write-tree`
+       # set up resetting
+       trap 'echo >&2 "Restoring index..."; git reset "$oldindex" .' EXIT
+       trap 'exit 1' INT TERM
+
+       echo >&2 "Creating index..."
+       git add -A
+fi
+
+echo >&2 "Listing candidates..."
+allrevs=`git rev-list "$@"`
+
+echo >&2 "Evaluating candidates..."
+bestrev=
+bestrevscore=
+for rev in $allrevs; do
+       score=`git diff $diffopts --cached "$rev" | wc -l`
+       if [ -z "$bestrevscore" ] || [ "$score" -lt "$bestrevscore" ]; then
+               echo >&2 "Improved to $rev (score: $score)"
+               bestrev=$rev
+               bestrevscore=$score
+       fi
+done
+echo >&2 "Done."
+
+echo "$bestrev"
+git diff $diffopts --cached "$bestrev" >&2