This is outdated, there's an improved version located here: https://github.com/foundObjects/sbc-flasher friendly/easy sd/usb/emmc image writer with verification and support for compressed images

flasher.sh

#!/usr/bin/env bash
#
# flasher.sh -- SBC image writer script with media verification
#
# source:  https://gist.github.com/foundObjects/0645ba25bd3f97ae9ee7f41ce6a4fde1
# contact: Arglebargle @ forum.pine64.org or https://github.com/foundObjects/
# license: http://www.wtfpl.net/txt/copying/
#
# usage: flasher.sh (--verify-only) image target

__main() {
  verify_only=''
  PARAMS=()
  while (("$#")); do
    [[ $1 == --*=* ]] || [[ $1 == -?=* ]] &&
      set -- "${1%%=*}" "${1#*=}" "${@:2}"
    case "$1" in
      -V | --verify | --verify-only)
        verify_only='true'
        shift
        ;;
      --help)
        _usage
        exit
        ;;
      --) # end argument parsing
        shift
        break
        ;;
      -*) # unsupported flags
        echo "Error: Unsupported flag $1" >&2
        _usage
        exit 1
        ;;
      *) # preserve positional arguments
        PARAMS+=("$1")
        shift
        ;;
    esac
  done
  set -- "${PARAMS[@]}"

  # standard flow: write image, then verify
  # if --verify-only flag passed then just verify

  if [[ -r "$1" ]] && [[ -b "$2" ]]; then
    # $1 is a readable file, $2 is a block device, flags parsed
    [[ $verify_only ]] || if _write "$1" "$2"; then
      echo "Write successful"
    else
      echo "Write failed"
      exit 1
    fi

    if _verify "$1" "$2"; then
      echo "Image verified successfully"
    else
      echo "Verify failed"
      exit 1
    fi
  else
    _usage
    exit 1
  fi
  exit 0
}

_usage() { echo "Usage: $0 (--verify-only) image target"; }

_verify() (
  set -euo pipefail &>/dev/null
  case "$(file -b "$1")" in
    "DOS/MBR boot sector;"*)
      echo "Verifying raw image"
      _size="$(stat -c '%s' "$1")"
      pv -s "$_size" "$1" | cmp -s -n "$_size" "$2"
      ;;
    "XZ compressed data")
      echo "Verifying xz image"
      _size="$(xz --robot --list "$1" | grep totals | awk '{ print $5 }')"
      pv -s "$_size" <(xz -T0 -dkqc "$1") | cmp -s -n "$_size" "$2"
      ;;
    *)
      echo "Unknown image type"
      return 1
      ;;
  esac
)

_write() (
  set -euo pipefail &>/dev/null
  case $(file -b "$1") in
    "DOS/MBR boot sector;"*)
      echo "writing raw image to $2"
      dd if="$1" of="$2" bs=4M conv=fsync status=progress
      ;;
    "XZ compressed data")
      echo "writing xz compressed image to $2"
      xz -T0 -dkqc "$1" | dd of="$2" bs=4M conv=fsync status=progress
      ;;
    *)
      echo "Unknown image type"
      return 1
      ;;
  esac
)

__main "$@"