Problem with nested quotes in bash: mongodump with query in a docker container via ssh

Question

I'm backing up my database that's in a docker container, and since the total filesize is too large to fit onto the remaining disk space I execute it via SSH and dump it onto my local pc with this command (I'm using Ubuntu default bash):

docker-machine ssh my-machine-image "docker exec container-id /bin/sh -c 'mongodump --archive -u=admin --authenticationDatabase=admin -p=mongo-pwd --db=my-db --collection=my-collection --gzip'" > myfile.dump

This works pretty great, however I'm having trouble getting it to work with the --query command. Mongodump requires it to be in strict JSON and I'm having trouble with getting the nested quotes in bash to work. My most successful attempt (aka it actually successfuly executed the command instead of returning a syntax/JSON error) was with a string literal like this, however that seems to parse the JSON wrong, since it always returns 0 documents, no matter the query:

docker-machine ssh my-machine-image "docker exec container-id /bin/sh -c $'mongodump --archive -u=admin --authenticationDatabase=admin -p=mongo-pwd --db=my-db --collection=my-collection --query=\'{ \"_id\": { \"$oid\": \"some_random_object_id\" } }\' --gzip'" > myfile.dump

What is the correct way to pass strict JSON to the --query parameter with this amount of nested quotes?

Socowi · Accepted Answer · 2020-05-19 16:33:43Z

2

Since you have multiple layers of quoting it would be easiest to assign each layer to a variable. Then use bash's printf %q to automatically quote any string for use in a shell.

#! /usr/bin/env bash
json='{"_id": { "'"$oid"'": "some_random_object_id" } }'
cmd="mongodump --archive -u=admin --authenticationDatabase=admin -p=mongo-pwd --db=my-db --collection=my-collection --query=$(printf %q "$json") --gzip"
sshCmd="docker exec container-id /bin/sh -c $(printf %q "$cmd")"

docker-machine ssh my-machine-image "$sshCmd"

answered May 19, 2020 at 16:33

Socowi

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