Dockerfile if else condition with external arguments

Question

I have dockerfile  FROM centos 7 ENV foo 42   then I build it   docker build -t my docker     and run it   docker run -it -d  my docker   Is it possible to pass arguments from command line and use it with if else in Dockerfile  I mean something like  FROM centos 7 if  my arg  42        ENV TRUE  else        ENV FALSE    and build with this argument    docker build -t my docker   --my arg 42

User · Answer

From some reason most of the answers here didn't help me (maybe it's related to my FROM image in the Dockerfile)

So I preferred to create a bash script in my workspace combined with --build-arg in order to handle if statement while Docker build by checking if the argument is empty or not

Bash script:

#!/bin/bash -x

if test -z $1 ; then 
    echo "The arg is empty"
    ....do something....
else 
    echo "The arg is not empty: $1"
    ....do something else....
fi

Dockerfile:

FROM ...
....
ARG arg
COPY bash.sh /tmp/  
RUN chmod u+x /tmp/bash.sh && /tmp/bash.sh $arg
....

Docker Build:

docker build --pull -f "Dockerfile" -t $SERVICE_NAME --build-arg arg="yes" .

Remark: This will go to the else (false) in the bash script

docker build --pull -f "Dockerfile" -t $SERVICE_NAME .

Remark: This will go to the if (true)

Edit 1:

After several tries I have found the following article and this one which helped me to understand 2 things:

1) ARG before FROM is outside of the build

2) The default shell is /bin/sh which means that the if else is working a little bit different in the docker build. for example you need only one "=" instead of "==" to compare strings.

So you can do this inside the Dockerfile

ARG argname=false   #default argument when not provided in the --build-arg
RUN if [ "$argname" = "false" ] ; then echo 'false'; else echo 'true'; fi

and in the docker build:

docker build --pull -f "Dockerfile" --label "service_name=${SERVICE_NAME}" -t $SERVICE_NAME --build-arg argname=true .

User · Answer

Exactly as others told  shell script would help  Just an additional case  IMHO it s worth mentioning  for someone else who stumble upon here  looking for an easier case   that is Environment replacement   Environment variables  declared with the ENV statement  can also be used in certain instructions as variables to be interpreted by the Dockerfile  The   variable name  syntax also supports a few of the standard bash modifiers as specified below     variable -word  indicates that if variable is set then the result will be that value  If variable is not set then word will be the result     variable  word  indicates that if variable is set then word will be the result  otherwise the result is the empty string

User · Answer

Using Bash script and Alpine Centos   Dockerfile   FROM alpine   just change this to centos   ARG MYARG    ENV E MYARG  MYARG  ADD    tmp RUN chmod  x  tmp script sh  amp  amp   tmp script sh   script sh      usr bin env sh  if   -z   E MYARG     then     echo  NO PARAM PASSED  else     echo  E MYARG fi   Passing arg   docker build -t test --build-arg MYARG  this is a test          Step 5 5   RUN chmod  x  tmp script sh  amp  amp   tmp script sh  --- gt  Running in 10b0e07e33fc this is a test Removing intermediate container 10b0e07e33fc  --- gt  f6f085ffb284 Successfully built f6f085ffb284   Without arg  docker build -t test         Step 5 5   RUN chmod  x  tmp script sh  amp  amp   tmp script sh  --- gt  Running in b89210b0cac0 NO PARAM PASSED Removing intermediate container b89210b0cac0

User · Answer

The accepted answer may solve the question  but if you want multiline if conditions in the dockerfile  you can do that placing   at the end of each line  similar to how you would do in a shell script  and ending each command with    You can even define someting like set -eux as the 1st command   Example   RUN set -eux      if   -f  path to file    then       mv  path to file  dest      fi      if   -d  path to dir    then       mv  path to dir  dest      fi   In your case   FROM centos 7 ARG arg RUN if   -z   arg      then       echo Argument not provided      else       echo Argument is  arg      fi   Then build with   docker build -t my docker   --build-arg arg 42

User · Answer

Just use the  test  binary directly to do this  You also should use the noop command     if you don t want to specify an  else  condition  so docker does not stop with a non zero return value error   RUN test -z   YOURVAR     echo  var is set   amp  amp  echo  var is not set  RUN test -z   YOURVAR   amp  amp  echo  var is not set       RUN test -z   YOURVAR     echo  var is set   amp  amp

User · Answer

It might not look that clean but you can have your Dockerfile  conditional  as follow  FROM centos 7 ARG arg RUN if    -z  quot  arg quot       then echo Argument not provided   else echo Argument is  arg   fi  and then build the image as  docker build -t my docker    --build-arg arg 45 or docker build -t my docker

User · Answer

You can use the conditional system that best fits your needs  Dockerfile ARG ENV  FROM foo as base  ARG ENV    run common RUN        For long running tasks that would slow down deployments RUN if     quot  ENV quot      quot dev quot       then           yum install -y lots of big dev packages         fi    Build dev image FROM base as image-dev  RUN     COPY        Build prod image FROM base as image-prod  RUN     COPY      FROM image- ENV AS final  Note that we define ENV twice - you need to define ENV globally  and in each image where it is used  Use docker  docker build -t my docker   --build-arg ENV  quot dev quot   Use docker-compose  version   3   services     dev      container name  dev     ports        - 3000 8080     volumes        -     var task     tty  true     build        context          dockerfile  Dockerfile       args          ENV  dev  docker-compose build --no-cache dev  amp  amp  docker-compose up dev

User · Answer

According to the doc for the docker build command  there is a parameter called --build-arg   Example usage   docker build --build-arg HTTP PROXY http   10 20 30 2 1234     IMO it s what you need

User · Answer

I had a similar issue for setting proxy server on a container  The solution I m using is an entrypoint script  and another script for environment variables configuration  Using RUN  you assure the configuration script runs on build  and ENTRYPOINT when you run the container  --build-arg is used on command line to set proxy user and password  As I need the same environment variables on container startup  I used a file to  quot persist quot  it from build to run  The entrypoint script looks like     bin bash   Load the script of environment variables    root configproxy sh   Run the main container command exec  quot    quot   configproxy sh    bin bash  function start config   read u p  lt   root proxy credentials  export HTTP PROXY http    u  p proxy com 8080 export HTTPS PROXY https    u  p proxy com 8080   bin cat  lt  lt EOF  gt   etc apt apt conf  Acquire  http  proxy  quot http    u  p proxy com 8080 quot   Acquire  https  proxy  quot https    u  p proxy com 8080 quot   EOF    if   -s  quot  root proxy credentials quot    then start config fi  And in the Dockerfile  configure    Base Image FROM ubuntu 18 04  ARG user ARG pass  USER root    -z the length of STRING is zero      are an alias for test command   if  user is not empty  write credentials file RUN if     -z  quot  user quot     then echo  quot   user    pass  quot  gt  root proxy credentials   fi   copy bash scripts COPY configproxy sh  root COPY startup sh    RUN   quot  bin bash quot    quot -c quot    quot    root configproxy sh quot      Install dependencies and tools  RUN apt-get update -y  amp  amp         apt-get install -yqq --no-install-recommends        vim iputils-ping  ENTRYPOINT   quot   startup sh quot   CMD   quot sh quot    quot -c quot    quot bash quot    Build without proxy settings docker build -t img01 -f Dockerfile     Build with proxy settings docker build -t img01 --build-arg user  lt USER gt  --build-arg pass  lt PASS gt  -f Dockerfile     Take a look here

User · Answer

There is an interesting alternative to the proposed solutions  that works with a single Dockerfile  require only a single call to docker build per conditional build and avoids bash  Solution  The following Dockerfile solves that problem  Copy-paste it and try it yourself  ARG my arg  FROM centos 7 AS base RUN echo  quot do stuff with the centos image quot   FROM base AS branch-version-1 RUN echo  quot this is the stage that sets VAR TRUE quot  ENV VAR TRUE  FROM base AS branch-version-2 RUN echo  quot this is the stage that sets VAR FALSE quot  ENV VAR FALSE  FROM branch-version-  my arg  AS final RUN echo  quot VAR is equal to   VAR  quot   Explanation of Dockerfile  We first get a base image  centos 7 in your case  and put it into its own stage  The base stage should contain things that you want to do before the condition  After that  we have two more stages  representing the branches of our condition  branch-version-1 and branch-version-2  We build both of them  The final stage than chooses one of these stages  based on my arg  Conditional Dockerfile  There you go  Output when running   I abbreviated this a little     my arg  2 docker build --build-arg my arg 2   Step 1 12   ARG my arg Step 2 12   ARG ENV Step 3 12   FROM centos 7 AS base Step 4 12   RUN echo  quot do stuff with the centos image quot  do stuff with the centos image Step 5 12   FROM base AS branch-version-1 Step 6 12   RUN echo  quot this is the stage that sets VAR TRUE quot  this is the stage that sets VAR TRUE Step 7 12   ENV VAR TRUE Step 8 12   FROM base AS branch-version-2 Step 9 12   RUN echo  quot this is the stage that sets VAR FALSE quot  this is the stage that sets VAR FALSE Step 10 12   ENV VAR FALSE Step 11 12   FROM branch-version-  my arg  Step 12 12   RUN echo  quot VAR is equal to   VAR  quot  VAR is equal to FALSE  my arg  1 docker build --build-arg my arg 1       Step 11 12   FROM branch-version-  my arg  Step 12 12   RUN echo  quot VAR is equal to   VAR  quot  VAR is equal to TRUE  Thanks to T  nis for this amazing idea

[docker] Dockerfile if else condition with external arguments

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