Plug git directories between repos with history

git-paste

#!/bin/bash -ue

usage() {
    echo "Usage: $0 srcdir[#ref] dstdir[#ref]"
    echo
    echo "Pastes between subdirectories of git repositories,"
    echo "preserving history"
}

SRC="$1"; shift
DST="$1"; shift
if [ $# -gt 0 ]; then usage; exit 2; fi

SRCBRANCH=${SRC#*#}
SRC=${SRC%#*}
if [ x"$SRC" = x"$SRCBRANCH" ]; then SRCBRANCH=master; fi
SRC=$(readlink -f "$SRC")
SRCGIT=$(cd "$SRC" && git rev-parse --show-toplevel)
SRCDIR=.${SRC##$SRCGIT}

DSTBRANCH=${DST#*#}
DST=${DST%#*}
if [ x"$DST" = x"$DSTBRANCH" ]; then DSTBRANCH=master; fi
mkdir -p "$DST"
DST=$(readlink -f "$DST")
DSTGIT=$(cd "$DST" && git rev-parse --show-toplevel)
DSTDIR=.${DST##$DSTGIT}

TMP=$(mktemp -d /tmp/git-graft.XXXXX)
trap "rm -rf /tmp/${TMP#/tmp/}" EXIT
echo "=== pasting dir $SRCDIR from $SRCGIT at $SRCBRANCH"
echo "=== to dir $DSTDIR within $DSTGIT at $DSTBRANCH"
echo "=== using temp dir $TMP"

cd $TMP
git clone -- "$SRCGIT" src
cd src

if [ x"$SRCDIR" != x"." ]; then
    git filter-branch --subdirectory-filter "${SRCDIR#./}"
fi
if [ x"$DSTDIR" != x"." ]; then
    git filter-branch -f --index-filter '\
      git ls-files -s | \
      sed "s#\t#&'"${DSTDIR#./}"'/#" | \
      GIT_INDEX_FILE=.gitindex.new git update-index --index-info && \
      (mv .gitindex.new $GIT_INDEX_FILE || true)'
fi
cd $DSTGIT
BRANCH=graft-from-${SRCGIT##*/}${SRCDIR//\//-}
BRANCH=${BRANCH//./}
git fetch "$TMP/src"

MERGED=$(git branch --merged $DSTBRANCH $BRANCH)
if [ -n "$MERGED" ]; then
    git rebase --preserve-merges $BRANCH FETCH_HEAD
    git checkout -B $BRANCH HEAD
    git checkout $DSTBRANCH
    git merge $BRANCH
else
    git branch -f $BRANCH FETCH_HEAD
    git merge $BRANCH
fi