Use inline comments in docker-compose command

Question

In my docker-compose.yml I need to use a very long command, and I want to document it. This is not easily done, but I have a workaround that's ALMOST working.

foo:                                    # valid comment
  image: foo:latest                     # valid comment
  command: >
           printf '
           something                    # explanation for this command
           --arg                        # explanation for this switch
           --a                          # explanation
           --b hello
           -c                           # this does...
           --d spam                     # don't use this when...
           #some notes
           --e ham                      # hmmm
           --eggs                       # explanation
           ' |grep -v ^[[:space:]]*$ |grep -v ^# |cut -d# -f1   # valid comment
  restart: always                       # valid comment

So every command and switch can be commented.

The bash:

printf ' ... ' prints all the stuff as text, to be run as a command
grep -v ^[[:space:]]*$ ignores the first empty line
grep -v ^# ignores comment lines
cut -d# -f1 strips inline comments from each line

This trick works perfectly in the shell !

However docker-compose up says:

ERROR: Invalid interpolation format for "command" option in service "foo": "printf ' something ...

If I escape the $ as $$ it says:

ERROR: for foo No closing quotation

How can I get this to work?

Try to escape the $ sign with another $. You will get rid of the invalid interpolation error. — b0gusb
– b0gusb, Commented Sep 26, 2019 at 13:26
@b0gusb Thanks that was a good idea, but now it says ERROR: for foo No closing quotation — lonix
– lonix, Commented Sep 26, 2019 at 15:18
Also, an issue probably comes from the quote in # don't … — ErikMD
– ErikMD, Commented Sep 26, 2019 at 20:47
@ErikMD No that is handled by the cut that strips inline comments — lonix
– lonix, Commented Sep 27, 2019 at 7:11

lonix · Accepted Answer · 2019-09-26 15:34:23Z

27

Here's a better way. The command docs don't show it, but I think it's standard YAML, so it's allowed.

foo:                               # valid comment
  image: foo:latest                # valid comment
  command:
    - something                    # explanation for this command
    - --arg                        # explanation for this switch
    - --a                          # explanation
    - --b hello
    - -c                           # this does...
    - --d spam                     # don't use this when...
    #some notes
    - --e ham                      # hmmm
    - --eggs                       # explanation
  restart: always                  # valid comment

answered Sep 26, 2019 at 15:34

lonix

22.4k32 gold badges149 silver badges300 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

mvc Over a year ago

For some reason this does not work for me :(

lonix Over a year ago

@mvc I suggest you open a separate question with a minimal reproducible sample.

Collectives™ on Stack Overflow

Use inline comments in docker-compose command

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related