dkr2sh - convert Dockerfile to shell script

This script naively translates some Dockerfile instructions into corresponding shell commands.

Usage

The file to use is dkr2sh.sed, which is a sed script, note how it starts:

#!/bin/sed -f
# Convert Dockerfile to shell script.

To use it, normal sed usage implies it takes stdin and outputs stdout. So:

./dkr2sh.sed < Dockerfile > mydockerscript.sh

Contributing

The explanation of the tranform rules below matches with .sh files, eg. copy-from.sh, copy.sh and add.sh

In the dkr2sh.sed file, the transform rules have been translated to sed patterns. The sh2sed.sh is the helper script that can do this as part of manual labour. You can change any of the patterns and run, eg. ./sh2sed.sh < copy-from.sh and you will get this:

for i in ARGS; do\n\ttest -d "$i" \&\& i="$i\/"\n\trsync -a "$i" DEST # FROM\ndone

It matches the replacement string in the dkr2sh.sed file, here, but with match groups inserted inplace of ARGS, DEST, FROM

s/^[[:space:]]*COPY\([[:space:]]\+--from=[^[:space:]]\+\)\(\([[:space:]]\+[^[:space:]]\+\)\+\)\([[:space:]]\+[^[:space:]]\+\)[[:space:]]*/for i in\2; do\n\ttest -d "$i" \&\& i="$i\/"\n\trsync -a "$i"\4 #\1\ndone/i

Each match group and result has to be implemented manually.

Conversion Rules

Instructions commented out

• FROM
• CMD
• LABEL
• MAINTAINER
• EXPOSE
• ENTRYPOINT
• VOLUME
• ONBUILD
• STOPSIGNAL
• HEALTHCHECK

Translate these instructions manually:

• USER - execute the next block(s) with su or equivalent
• SHELL - unwrap JSON-formatted arguments, run it for subsequent block(s)

Additionally, any pure comment lines (starting with #) are removed during conversion in order to support multi-line RUN statements with embedded comments, which is standard Dockerfile practise.

ENV

Before:

ENV FOO bar
ENV FOO=bar
ENV FOO

After:

export FOO=bar
export FOO=bar
# (no value assigned) ENV FOO

ARG

Same as ENV

RUN

Before:

RUN /usr/bin/foo \
    && /sbin/bar --quux

After:

/usr/bin/foo \
    && /sbin/bar --quux

COPY

COPY behaves differently on files and directories, so we use rsync to emulate recursive content copying on directories.

If --from argument is given, it becomes just a comment, because unlike Docker images (and ogres), shell scripts don't have layers.

Before:

COPY --from=composer foo.sh /usr/local/bin/

After:

for i in foo.sh; do
        test -d "$i" && i="$i/"
        rsync -a "$i" /usr/local/bin/ # --from=composer
done

WORKDIR

Before:

WORKDIR /var/lib/pgsql/10.1

After:

mkdir -p /var/lib/pgsql/10.1 && cd /var/lib/pgsql/10.1

ADD

ADD has many rules, and transforms into a fairly large snippet.

Before:

ADD https://example.org/foo.bin /opt

After:

if echo "/opt" | grep -q '/$'; then
        mkdir -p "/opt";
else
        mkdir -p "$(dirname "/opt")";
fi

for i in https://example.org/foo.bin; do
        if echo "$i" | grep -q '^\(https\?\|ftp\)://'; then
                if echo "/opt" | grep -q '/$'; then
                        (cd "/opt" && wget -q "$i");
                else
                        wget -q -O "/opt" "$i";
                fi
        elif test -d "$i"; then
                rsync -a "$i/" "/opt";
        elif tar -tf "$i" >/dev/null 2>&1; then
                mkdir -p "/opt" && tar -C "/opt" -xf "$i";
        else
                rsync -a "$i" "/opt";
        fi
done

Copyright

Copyright 2018, Development Gateway

Copyright 2022, Dennis Schneidermann - modifications stated in source

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.