How do I make a comment in a Dockerfile

Question

I am writing a Dockerfile  Is there a way to make comments in this file   Does Docker have a comment option that takes the rest of a line and ignores it

User · Accepted Answer

You can use   at the beginning of a line to start a comment  whitespaces before   are allowed     do some stuff RUN apt-get update         install some packages     apt-get install -y cron    s in the middle of a string are passed to the command itself  e g   RUN echo  we are running some   of cool things

User · Answer

Dockerfile comments start with      just like Python  Here is a good example  kstaken dockerfile-examples      Install a more-up-to date version of MongoDB than what is included in the default Ubuntu repositories   FROM ubuntu MAINTAINER Kimbro Staken  RUN apt-key adv --keyserver keyserver ubuntu com --recv 7F0CEB10 RUN echo  deb http   downloads-distro mongodb org repo ubuntu-upstart dist 10gen    tee -a  etc apt sources list d 10gen list RUN apt-get update RUN apt-get -y install apt-utils RUN apt-get -y install mongodb-10gen   RUN echo     gt  gt   etc mongodb conf  CMD    usr bin mongod    --config     etc mongodb conf

User · Answer

Use the   syntax for comments  From  https   docs docker com engine reference builder  format    My comment here RUN echo  we are running some cool things

User · Answer

As others have mentioned  comments are referenced with a   and are documented here  However  unlike some languages  the   must be at the beginning of the line  If they occur part way through the line  they are interpreted as an argument and may result in unexpected behavior     This is a comment  COPY test dir target dir   This is not a comment  it is an argument to COPY  RUN echo hello world   This is an argument to RUN but the shell may ignore it   It should also be noted that parser directives have recently been added to the Dockerfile which have the same syntax as a comment  They need to appear at the top of the file  before any other comments or commands  Originally  this directive was added for changing the escape character to support Windows     escape    FROM microsoft nanoserver COPY testfile txt c   RUN dir c     The first line  while it appears to be a comment  is a parser directive to change the escape character to a backtick so that the COPY and RUN commands can use the backslash in the path  A parser directive is also used with BuildKit to change the frontend parser with a syntax line  See the experimental syntax for more details on how this is being used in practice   With a multi-line command  the commented lines are ignored  but you need to comment out every line individually     cat Dockerfile FROM busybox latest RUN echo first command      amp  amp  echo second command disabled     amp  amp  echo third command    docker build   Sending build context to Docker daemon  23 04kB Step 1 2   FROM busybox latest  --- gt  59788edf1f3e Step 2 2   RUN echo first command   amp  amp  echo third command  --- gt  Running in b1177e7b563d first command third command Removing intermediate container b1177e7b563d  --- gt  5442cfe321ac Successfully built 5442cfe321ac

User · Answer

Format  Here is the format of the Dockerfile   We can use   for commenting purpose Comment for example    FROM microsoft aspnetcore FROM microsoft dotnet COPY  publish  app WORKDIR  app ENTRYPOINT   dotnet    WebApp dll     From the above file when we build the docker  it skips the first line and goes to the next line because we have commented it using

User · Answer

this is comment this isn t comment  is the way to do it  You can place it anywhere in the line and anything that comes later will be ignored

User · Answer

Docker treats lines that begin with   as a comment  unless the line is a valid parser directive  A   marker anywhere else in a line is treated as an argument  example code    this line is a comment  RUN echo  we are running some   of cool things   Output  we are running some   of cool things

[docker] How do I make a comment in a Dockerfile?

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