git-patches

#!/bin/bash

################################################################################
#
#   Description:
#   ------------
#   Creates file-specific patches of a commit
#
#   Usage:
#   ------
#       $> git patches COMMIT
#
################################################################################

# Confirm that we are in a git repository
GIT_TOP=$(git rev-parse --show-toplevel)
RC=$?
if [ $RC != "0" ]; then
    exit $RC
fi

# Confirm correct number of arguments
if [ $# -ne 1 ]; then
    echo "Incorrect number of arguments."
    echo "Usage:"
    echo "    $> git patches <commit-hash>"
    exit 1
fi

COMMIT=$1

# Confirm the commit hash is valid
SHORT_HASH=$(git rev-parse --quiet --verify --short ${COMMIT})
if [ $? != "0" ]; then
    echo "${COMMIT} is not a valid git object"
    exit 1
fi

FILES_LIST=(`git diff-tree --no-commit-id --name-only -r ${COMMIT}`)

PATCH_FILES_DIR="/tmp/${SHORT_HASH}_patches"

if [ -e "${PATCH_FILES_DIR}" ]
then
    echo "Patch files directory '${PATCH_FILES_DIR}' already exists. Aborting."
    exit 2
else
    mkdir ${PATCH_FILES_DIR}
fi

NUM_PATCH_FILES=0
for (( i=0; i<${#FILES_LIST[@]}; ++i ))
do
    FULL_FILE_PATH=${FILES_LIST[$i]}

    if [ ! -e ${FULL_FILE_PATH} ]
    then
        echo -e "\e[33m'\e[34m${FULL_FILE_PATH}\e[33m' is not accessible from current commit. Skipping.\e[0m"
        continue
    fi

    FILE_WITH_UNDERSCORES=$(echo ${FULL_FILE_PATH} | sed 's/\//__/g')
    PATCH_FILE_NAME="${FILE_WITH_UNDERSCORES}.patch"

    # If the patch file name starts with a period, then replace the leading '.'
    # with 'dot__'. Otherwise, the generated patch file will be hidden, and
    # would therefore be susceptible to being overlooked.
    if [[ "${PATCH_FILE_NAME}" == .* ]]
    then
        PATCH_FILE_NAME=${PATCH_FILE_NAME/./"dot__"}
    fi

    ORIG_PATCH_FILE=$(git format-patch -1 ${COMMIT} ${FULL_FILE_PATH})
    mv "${ORIG_PATCH_FILE}" "${PATCH_FILES_DIR}/${PATCH_FILE_NAME}"
    NUM_PATCH_FILES=$(expr ${NUM_PATCH_FILES} + 1)
done

echo "Saved ${NUM_PATCH_FILES} patch files"
echo "To apply them selectively, use:"
echo "    git apply-from-dir ${PATCH_FILES_DIR}"