Runs a command wrapped with snapper pre-post snapshots for btrfs subvolumes. File path: /usr/local/bin

snp

#!/usr/bin/env bash
#
# Runs a command wrapped with snapper pre-post snapshots for btrfs subvolumes.
# Usage: snp [-c config1,config2,...] <command>

# Constants
readonly LOG_PATH='/var/local/log/snp'
readonly DATE="$(date +'%Y-%m-%d-%H%M%S')"
readonly LOG_FILE="${LOG_PATH}/snp-${DATE}.log"

#######################################
# Print out error messages to STDERR.
# Globals:
#   None
# Arguments:
#   Error
# Returns:
#   None
#######################################
err() {
  echo "[$(date +'%Y-%m-%d %H:%M:%S%z')] error: $@" 1>&2
}

#######################################
# Log STDOUT and STDERR.
# Reference: http://stackoverflow.com/questions/3173131/redirect-copy-of-stdout-to-log-file-from-within-bash-script-itself
# Globals:
#   None
# Arguments:
#   Path to log file
# Returns:
#   None
#######################################
log_stdout_stderr() {
  exec > >(tee -a "$@")
  exec 2> >(tee -a "$@" >&2)
}

# TODO(mubeeniqbal): Use of eval considered dangerous. Find an alternative to all eval commands.
main() {
  if [[ "${EUID}" -ne 0 ]]; then
    err 'snp: you cannot perform this operation unless you are root: Permission denied'
    exit 1
  fi
  
  if [[ ! -d "${LOG_PATH}" ]]; then
    mkdir -vp "${LOG_PATH}" || return
  fi
  
  log_stdout_stderr "${LOG_FILE}"
  
  # Snapper configs array.
  local -a CONFIGS=('root')
  
  # Populate the array if configs are provided in arguments.
  if [[ "$1" = '-c' ]]; then
    shift
    CONFIGS=(${1//,/ })
    shift
  fi
  
  # Make configs array constant.
  readonly CONFIGS
  local -ri CONFIG_COUNT="${#CONFIGS[@]}"
  
  # Save command to wrap with pre-post snapshots.
  local -r CMD="$@"
  
  # Declare local snapshot numbers array.
  local -a numbers
  local snapper_cmd
  
  echo '> Creating pre snapshots.'
  local -i i
  
  # Create pre snapshots.
  for ((i=0; i<"${CONFIG_COUNT}"; ++i)); do
    snapper_cmd="snapper --config=${CONFIGS[${i}]} create --type=pre --cleanup-algorithm=number --print-number --description=\"command: ${CMD}\""
    echo "> Running command: ${snapper_cmd}"
    numbers["${i}"]="$(eval "${snapper_cmd}")" || return
    echo "> Snapshot created: config:${CONFIGS[${i}]}, type:pre, number:${numbers[${i}]}"
  done
  
  # Run wrapped command.
  echo '> ---------------------------------------------------------------------'
  echo "> Running command: ${CMD}"
  eval "${CMD}"
  echo '> ---------------------------------------------------------------------'
  echo '> Creating post snapshots.'
  
  # Create post snapshots.
  for ((i=0; i<"${CONFIG_COUNT}"; ++i)); do
    snapper_cmd="snapper --config=${CONFIGS[${i}]} create --type=post --cleanup-algorithm=number --print-number --description=\"command: ${CMD}\" --pre-number=${numbers[${i}]}"
    echo "> Running command: ${snapper_cmd}"
    numbers["${i}"]="$(eval "${snapper_cmd}")" || return
    echo "> Snapshot created: config:${CONFIGS[${i}]}, type:post, number:${numbers[${i}]}"
  done
  
  exit 0
}

main "$@"

Why is that so? What effect does (( )) have over [[ ]]?

-c is exactly what I was looking for. Thank you!

Why do you always deny unless root? My .snapshots directory is accessible to me. (man snapper #PERMISSIONS)