passing arguments to docker exec from bash prompt and script

Question

I am trying to execute a command inside my mongodb docker container. From my linux command prompt it is pretty easy and works when I do this

docker exec -it d886e775dfad mongo --eval 'rs.isMaster()'

The above tells me to go to a container and execute the command

"mongo --eval 'rs.isMaster()' - This tells mongo to take rs.isMaster() as an input and execute it. This works and gives me the output.

Since I am trying to automate this via bash script, I did this

cmd="mongo --eval 'rs.isMaster()"

And then tried executing like this

docker -H $node2 exec d886e775dfad "$cmd"

But I guess somehow docker thinks that now the binary file inside the container is not mongo or sth else and it gives me the following error:

rpc error: code = 2 desc = oci runtime error: exec failed: container_linux.go:247: starting container process caused "exec: \"mongo --eval 'rs.isMaster()'\": executable file not found in $PATH"

b0gusb · Accepted Answer · 2019-01-04 14:22:46Z

31

docker exec -it d886e775dfad sh -c "mongo --eval 'rs.isMaster()'"

This calls the shell (sh) executing the script in quotation marks. Note that this also fixes things like wildcards (*) which otherwise do not work properly with docker exec.

edited Jan 4, 2019 at 14:22

b0gusb

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answered Oct 13, 2017 at 13:08

Stuart Holliday

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3 Comments

Noël Widmer Over a year ago

Can you explain why your solution works in order to raise the value of your contribution? Posting only code is often not very helpful.

Caleb Over a year ago

Why is -c not listed in docker exec --help?

JK Laiho Over a year ago

@Caleb it's a parameter to sh

BMitch · Accepted Answer · 2017-04-27 01:07:54Z

4

You need to run (there's a missing single quote in your example):

cmd="mongo --eval 'rs.isMaster()'"

Followed by (without the quotes around $cmd):

docker -H $node2 exec d886e775dfad $cmd

By including quotes around $cmd you were looking for the executable file mongo --eval 'rs.isMaster()' rather than the executable mongo with args mongo, --eval, and 'rs.isMaster()'.

answered Apr 27, 2017 at 1:07

BMitch

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Comments

Howard · Accepted Answer · 2017-04-27 00:49:24Z

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It looks as though mongo is interpreting the entire contents of $cmd as the command to execute. This makes sense because you are quoting the parameter on the command line. Essentially when you did ... exec "$cmd" the shell will interpret the dollar-sign and expand it to be the contents in-place. Next it will interpret the double-quotes and pass the entire inner contents (now being mongo --eval 'rs.isMaster()' as a single command line argument to the process. This should result in mongo looking for a program with the name mongo --eval 'rs.isMaster() in your path. Which obviously doesn't exist.

answered Apr 27, 2017 at 0:49

Howard

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2 Comments

curiousengineer Over a year ago

how do i fix this?

Howard Over a year ago

Oops sorry forgot the solution. Try omitting the quotes around the variable. Then it should expand the variable inline and turn into docker -H $node2 exec d886e775dfad mongo --eval 'rs.isMaster()'

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