Docker - make ADD command conditional on command line argument - docker

Question

Can ADD command be customised to work with command line argument.
Basically i have different versions of a file let's say file1 and file2, and based on some condition passed through command line.
The following command works correctly and transfers the file from host to docker, but i didn't find any references to do it conditionally.
ADD target/file.yml file.yml

Answer 1

No, ADD does not support the conditional way of copying files.
But there is a way to deal with such configuration while coping from Host.
Copy all configuration to some temp location in your case copy all file1 file2 to some /temp location, then base on ARG pass to docker build, move the file to target.
Or do the above using docker entrypoint based on ENV, instead of base on ARG
FROM alpine
ADD target/ /temp_target
RUN mkdir /target
#filename to be copied to the target
ARG file_name
# pass update_file true or false if true file wil be update to new that is passed to build-args
ARG update_file
ENV file_name=$file_name
ARG update_file=$update_file
#check if update_file is set and its value is true then copy the file from temp to target, else copy file1 to target
RUN if [ ! -z "$update_file" ] && [ "${update_file}" == true ];then \
echo "$update_file"; \
echo "echo file in temp_target"; \
ls /temp_target ;\
echo "updating file target" ;\
cp /temp_target/"${file_name}" /target/ ; \
echo "list of updated files in target"; \
ls /target ; \
else \
echo "copy with default file that is ${file_name}" ;\
cp /temp_target/file1 /target ;\
fi
Build:
This will not updated file, will copy with default filename that is file1
docker build --no-cache --build-arg file_name=file1 --build-arg update_file=false -t abc .
This will update file in the target, so the new file will be in the target is file2.
docker build --no-cache --build-arg file_name=file2 --build-arg update_file=true -t abc .