give a docker image name as an argument, get approximate dockerfile

image_to_dockerfile.sh

#!/bin/bash

docker history --no-trunc --format "{{.CreatedBy}}" $1 | # extract information from layers
tac                                                    | # reverse the file
sed 's,^\(|3.*\)\?/bin/\(ba\)\?sh -c,RUN,'             | # change /bin/(ba)?sh calls to RUN
sed 's,^RUN #(nop) *,,'                                | # remove RUN #(nop) calls for ENV,LABEL...
sed 's,  *&&  *, \\\n \&\& ,g'                           # pretty print multi command lines following Docker best practices