add git-split.sh

scripts/git-split.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+#
+# Copy a git file, keeping history.
+# Source: https://stackoverflow.com/a/53849613/3079831
+
+if (( $# != 2 )) ; then
+  echo "Usage: git-split.sh original copy"
+  exit 1
+fi
+
+from="$1"
+to="$2"
+
+git mv "$from" "$to"
+git commit -n -m "Split history $from to $to - rename file to target-name"
+REV=$(git rev-parse HEAD)
+git reset --hard HEAD^
+git mv "$from" temp
+git commit -n -m "Split history $from to $to - rename source-file to temp"
+git merge "$REV"
+git commit -a -n -m "Split history $from to $to - resolve conflict and keep both files"
+git mv temp "$from"
+git commit -n -m "Split history $from to $to - restore name of source-file"
+
+exit 0