unpkg - For extracting .pkg files on the macintosh

unpkg

#!/bin/zsh

# A functon that shows users how to use the script. It describes
# and offers some help text that appears when invoked without 
# parameters.
showUsage() {
  local tool="\x1b[1;35munpkg\x1b[22;39m"
  printf "${tool} <path-to-package.pkg> <destination-directory>\n\n"
  printf "${tool} will attempt to unpackage the \x1b[1m.pkg\x1b[0m file provided,\n"
  printf "however, if certain expectations are not met, it will stop and inform\n"
  printf "to the best of its ability, what you should do to continue manually.\n"
}

# Print a message when a file (first parameter) is missing from an
# indicated path
missingFile() {
  printf "The file specified ${1}, cannot be found.\n"
}

# Print a message when a directory (first parameter) is missing from
# an indicated path
missingDir() {
  printf "The directory ${1}, cannot be found.\n"
}

# Generate a random string of the supplied length, defaults to 8
# characters long.
randString() {
  local -a alpha
  local string=""
  local count="${1:-8}"
  local r=0

  for i in {a..z} {A..Z} {0..9}; do 
    alpha+=( "${i}" )
  done

  for ((i = 0; i < count; i++)); do
    r=$(($RANDOM % 62))
    string="${string}${alpha[$r]}"
  done

  printf "${string}"
}

# If we don't have at least two parameters, show the usage
# text and quit
if [[ "${#}" -lt 2 ]]; then
  showUsage
  exit 0
fi

# If the file cannot be found, show the missing file text
# and quit
if ! [[ -f "${1}" ]]; then
  missingFile "${1}"
  exit 1
fi

# If the output directory cannot be found, show the missing
# directory text and quit
if ! [[ -d "${2}" ]]; then
  missingDir "${2}"
  exit 1
fi

# Declare some local variables for file, output directory,
# temporary directory, and the current directory
local file="${1}"
local outDir="${2}"
local tmpDir="/tmp/$(randString)"
local curDir="$(pwd)"

# Remove the temporary directory and contents, if possible,
# return to the original directory and exit with the status
# code supplied (or defaults to 0) 
cleanup() {
  cd "${curDir}"
  rm 2>&1 >/dev/null -rf "${tmpDir}"
  
  if ! [[ "${?}" -eq 0 ]]; then
    printf "Could not remove temp directory '${tmpDir}'\n"
  fi
  
  exit ${1:-0}
}

# Create the temporary directory
mkdir -p "${tmpDir}"

# If we cannot create the temp directory, print a message,
# and cleanup with a status of 1
if ! [[ "$?" -eq 0 ]]; then
  printf "Could not create temporary directory ${tmpDir}\n"
  cleanup 1
fi

# Move to the temporary directory
cd "${tmpDir}"

# Extract, using xar, the package file
xar -xf "${file}"

# Within the extracted files, should be a file called Payload.
# Find the path to this file.
local payload="$(realpath $(find . -type f -name 'Payload'))"

# If we cannot find the Payload file, then stop and instruct the
# caller on what to do. At this point, we should not try to proceed
if [[ "${#payload}" -eq 0 ]]; then
  printf "Could not find a file called 'Payload' in the extracted contents.\n"
  printf "Find the file, move to your target directory, then run\n"
  printf "cat ${tmpDir}/path/to/file | gunzip -dc | cpio -i\n"
  exit 1
fi

# Move to the output directory
cd "${outDir}"

# Invoke the holy trinity of commands to extract the Payload file
cat "${payload}" | gunzip -dc | cpio -i

# Remove the temp directory as its contents are no longer needed
rm 2>&1 >/dev/null -rf "${tmpDir}"

# Let the user know if we could not clean up
if ! [[ "${?}" -eq 0 ]]; then
  printf "Could not remove ${tmpDir}"
fi

# Clean up and exit with status 0
cleanup