dpkg-repack0

#!/bin/sh
# dpkg-repack0 (part of ossobv/vcutil) // wdoekes/2024 // Public Domain
#
# Create a .deb file out of a package that has already been installed.
#
# This utility can make it easy to copy packages from one computer to another,
# or to recreate packages that are installed on your system, but no longer
# available elsewhere, or to store the current state of a package before you
# upgrade it.
#
# This utility does the same as dpkg-repack(1), which I did not know
# existed until I wrote this heading. That is also why I renamed it to
# dpkg-repack0.
#
# Differences between dpkg-repack0 and dpkg-repack:
# +====================================+====================================+
# | dpkg-repack0                       | dpkg-repack                        |
# +====================================+====================================+
# | Depends on just dpkg.              | Requires perl / libdpkg-perl.      |
# | Always adds +repack in version.    | Has options for version tags.      |
# | Has only one mode of operation.    | Has help / options.                |
# | Always adds repack info in desc.   | Keeps description as-is.           |
# | Does dumb conffile lookups.        | Does "skipping obsolete conffile". |
# | Makes reproducible packages.       | Keeps changing timestamps.         |
# +------------------------------------+------------------------------------+
#
# Example invocation:
#
#   $ dpkg -l vcutil | grep ^ii
#   ii  vcutil         1.50         all          OSSO ... sysadmin utilities
#
#   $ dpkg-repack0 vcutil
#   dpkg-deb: building package 'vcutil' in 'vcutil_1.50+repack_all.deb'.
#
set -eu

# Check if package name is provided
if [ -z "${1:-}" ]; then
    echo "Usage: $0 <package_name>" >&2
    exit 1
fi

PACKAGE_NAME="$1"
PACKAGE_VERSION=$(dpkg-query -W -f='${Version}' "$PACKAGE_NAME" |
        sed -e 's/:/%3a/g')
if [ -z "$PACKAGE_VERSION" ]; then
    echo "Package $PACKAGE_NAME is not installed."
    exit 1
fi
PACKAGE_ARCH=$(dpkg-query -W -f='${Architecture}' "$PACKAGE_NAME")
PACKAGE=${PACKAGE_NAME}_${PACKAGE_VERSION}+repack_${PACKAGE_ARCH}.deb

# Create a temporary directory to store the package contents
TEMP_DIR=$(mktemp -d)
umask 022
mkdir -p "$TEMP_DIR/DEBIAN"
trap 'rm -rf "$TEMP_DIR"' EXIT

# Fetch control files from /var/lib/dpkg/info/
sed -e '/^Package: '"$PACKAGE_NAME"'$/,/^$/!d;/^Status:/d;/^$/d' \
        /var/lib/dpkg/status >"$TEMP_DIR/DEBIAN/control"
for file in /var/lib/dpkg/info/${PACKAGE_NAME}.*; do
    basefile=$(basename "$file")
    shortfile=${basefile#${PACKAGE_NAME}.}
    case $shortfile in
        list);;
        *) cp -a "$file" "$TEMP_DIR/DEBIAN/$shortfile";;
    esac
done

# Copy installed files listed by dpkg -L
cat /var/lib/dpkg/info/${PACKAGE_NAME}.list | while read -r file; do
    # Skip directories
    if [ -d "$file" ]; then
        continue
    fi

    # Warn about, but ignore missing files
    if [ ! -e "$file" ]; then
        echo "$file: not found on filesystem, skipping.." >&2
        continue
    fi

    DEST_DIR="$TEMP_DIR$(dirname "$file")"
    mkdir -p "$DEST_DIR"

    # Copy file
    cp -a "$file" "$DEST_DIR"
done

# Clean up timestamps/modes
chmod 0755 "$TEMP_DIR"
SOURCE_DATE_EPOCH=$(\
    dpkg-parsechangelog 2>/dev/null |
    awk 'BEGIN{s=0} /^Timestamp:/{s=$2} END{print s}')

# Build the package
if command -v fakeroot >/dev/null; then
    SOURCE_DATE_EPOCH=$SOURCE_DATE_EPOCH \
    exec fakeroot -- dpkg-deb --build "$TEMP_DIR" "${PACKAGE}"
else
    echo "$0: fakeroot not found, repacking as current user" >&2
    SOURCE_DATE_EPOCH=$SOURCE_DATE_EPOCH \
    exec dpkg-deb --build "$TEMP_DIR" "${PACKAGE}"
fi