$ go get github.com/jessfraz/dockfmt

$ dockfmt -h
dockfmt -  Dockerfile format.

Usage: dockfmt <command>

Flags:

  -d, --debug  enable debug logging (default: false)

Commands:

  base        List the base image used in the Dockerfile(s).
  dump        Dump parsed Dockerfile(s).
  fmt         Format the Dockerfile(s).
  maintainer  List the maintainer for the Dockerfile(s).
  version     Show the version information.

$ dockfmt fmt -h
Usage: dockfmt fmt [OPTIONS] DOCKERFILE [DOCKERFILE...]

Format the Dockerfile(s).

Flags:

  -D, --diff   display diffs instead of rewriting files (default: false)
  -d, --debug  enable debug logging (default: false)
  -l, --list   list files whose formatting differs from dockfmt's (default: false)
  -w, --write  write result to (source) file instead of stdout (default: false)

$ dockfmt format -d htop/Dockerfile
diff htop/Dockerfile dockfmt/htop/Dockerfile
--- /tmp/dockfmt143910590	2016-09-19 15:59:22.612250710 -0700
+++ /tmp/dockfmt412224773	2016-09-19 15:59:22.612250710 -0700
@@ -4,10 +4,11 @@
 # 	--pid host \
 # 	jess/htop
 #
-FROM alpine:latest
-MAINTAINER Jessie Frazelle <[email protected]>
+
+FROM	alpine:latest
+MAINTAINER	Jessie Frazelle <[email protected]>

-RUN apk --no-cache add \
+RUN	apk add --no-cache \
 	htop

-CMD [ "htop" ]
+CMD	["htop"]

$ dockfmt fmt -l */Dockerfile */*/Dockerfile
ab/Dockerfile
afterthedeadline/Dockerfile
android-tools/Dockerfile
ansible/Dockerfile
apt-file/Dockerfile
atom/Dockerfile
audacity/Dockerfile
awscli/Dockerfile
beeswithmachineguns/Dockerfile
buttslock/Dockerfile
camlistore/Dockerfile
cathode/Dockerfile
...

$ dockfmt base */Dockerfile */*/Dockerfile
BASE                          COUNT
debian:stretch                50
alpine:latest                 30
debian:sid                    28
ubuntu:16.04                  12
alpine:edge                   7
python:2-alpine               3
ruby:alpine                   2
java:7-alpine                 2
r.j3ss.co/wine                1
kalilinux/kali-linux-docker   1
haskell                       1
mhart/alpine-node:5           1
r.j3ss.co/cpuminer            1
opensuse                      1
java:8-alpine                 1
golang:latest                 1

$ dockfmt maintainer */Dockerfile */*/Dockerfile
MAINTAINER                                      COUNT
Jessie Frazelle <[email protected]>                113
Christian Koep <[email protected]>      11
Justin Garrison <[email protected]>   2
Daniel Romero <[email protected]>             1
Cris G [email protected]                         1