git-append-repo

#!/bin/bash

# in repo R# git-append-repo S foo
# # where S is a repository (remote or local), and foo is a (not yet existing) subdirectory of the current directory,
# #  which must be located in the working directory of another repository (let's call that repository R)
# =>
# say R's commit history was R1--R2--R3--R4 and S's was S1--S2--S3, then after the command completes, R will have history R1--R2--R3--R4--S1'--S2'--S3'
# where any Sx' will be identical to Sx except that any path a/b/c in Sx will be foo/a/b/c in Sx'

set -e

git status >/dev/null  # make sure we're in a git repo

repo="$1"
subdir="$2"
repobranch="${3:-master}"

if [ -z "$repo" -o -z "$subdir" -o -e "$subdir" ]; then
    echo "usage: $0 <git repo> <subdir to be created>" >&2
    exit 1
fi

git fetch -q $repo $repobranch

git rev-list --reverse FETCH_HEAD | while read commit; do

    echo "processing commit $commit" >&2

    rm -rf "$subdir"
    mkdir -p "$subdir"

    git ls-tree -r -z --full-name --full-tree $commit | while read -d $'\0' line; do

        read mode type id path <<<"$line"

        if [ "$type" != "blob" ]; then
            echo "non-blob ($type) object $id in commit $commit" >&2
            continue
        fi

        echo "file: blob=$id mode=$mode path=$path" >&2

        pathdir=$(dirname "$path")
        mkdir -p "$subdir/$pathdir"
        git show "$id" >"$subdir/$path"
        chmod "${mode#??}" "$subdir/$path"
    done

    git add -A "$subdir"

    git commit -C "$commit"
done