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Dockerfile alternatives for heredoc
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| #printf | |
| RUN printf '#!/bin/bash\n\ | |
| echo hello world from line 1\n\ | |
| echo hello world from line 2'\ | |
| >> /tmp/hello | |
| #echo | |
| RUN echo -e '#!/bin/bash\n\ | |
| echo hello world from line 1\n\ | |
| echo hello world from line 2'\ | |
| >> /tmp/hello |
Yes, heredoc support is great.
I did some decrypting of data etc in a dockerfile entrypoint and embedded the script so no external files were required. But developing this took longer than expected because of different levels of quote escaping, subshells and parameter substitution or escaping ... It was fun but nothing you would want to revisit later. And a nightmare to debug.
An excerpt below: (DECRYPT_* are docker run environment variables)
RUN printf '%s\n' \
'#!/bin/bash' \
'' \
'DATA_DIR=/mnt/data' \
'echo "Data dir: ${DATA_DIR} ... $(du -sh ${DATA_DIR} | cut -f1)"' \
'' \
'echo "* Decrypt data ..."' \
' ( \' \
' KEY="${DECRYPT_KEY}" IV="${DECRYPT_IV}" \' \
' bash -c " \' \
' find ${DATA_DIR} -iname '"'"'*.jsonl.bz2.enc'"'"' -type f -exec \' \
' bash -c '"'"' \' \
' FILE="\${0%.enc}"; \' \
' openssl aes-256-cbc -K \${KEY} -iv \${IV} -d -in \"\${FILE}.enc\" -out \"\${FILE}\"' \
" '"' {} \; \' \
' " \' \
' )' \
'' \
'echo "* Decompress data ..."' \
'find ${DATA_DIR} -iname '"'*.jsonl.bz2'"' -type f -exec bzip2 -d {} \;' \
'' \
'echo "* Cleanup data ..."' \
'# remove encrypted and compressed data' \
'find ${DATA_DIR} -iname '"'*.jsonl.bz2.enc'"' -type f -exec rm {} \;' \
'find ${DATA_DIR} -iname '"'*.jsonl.bz2'"' -type f -exec rm {} \;' \
'' \
'echo "Data dir (ready): $(du -sh ${DATA_DIR} | cut -f1)"' \
'' \
'echo -e "\nDataset list:"' \
'ls -1shR ${DATA_DIR}/*' \
'' \
> prepare_data.sh && \
chmod +x prepare_data.sh
Also, there is official way to do it:
# syntax=docker/dockerfile:1.3-labs
RUN <<EOF
echo "Hello" >> /hello
echo "World!" >> /hello
EOFI use it as the following:
# syntax=docker/dockerfile:1.4
RUN cat <<EOF >> /usr/local/bin/startup.sh
if [ \$# -gt 0 ]; then
exec "\$@"
else
/usr/bin/tini -- /usr/local/bin/jenkins.sh
fi
EOF
kudos @maxx27! I was banging my head why in 2024 it still has to be so difficult to use heredocs in Dockerfiles in a reasonable way. That last snippet of yours is the way to go! Thanks!
FROM debian
RUN <<EOT bash
set -eux
to_install=(
vim
)
apt-get update
failing_command # set -e exit with non-zero status
apt-get install -y "\${to_install[@]}"
EOT
# execute list shell
RUN <<EOF
apt-get update
apt-get upgrade -y
apt-get install -y ...
EOF
# run python
RUN <<EOF
#!/usr/bin/env python3
with open("/hello", "w") as f:
print("Hello", file=f)
print("World", file=f)
EOF
# create index.html
COPY <<EOF /usr/share/nginx/html/index.html
<html>hello, index</html>
EOF
# create /etc/mysql/my.cnf
RUN <<-EOF > /etc/mysql/my.cnf
[mysqld]
user=root
datadir=/app/mysql
port=3306
log-bin=/app/mysql/mysql-bin
EOF
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@Querela agreed, it's not a good solution for persistent Dockerfiles. Later on in the script I pipe the string into
docker build -so there's never a Dockerfile for anyone to read and be confused about. heredoc support in buildkit seems even better though.