How to pass environment variable to mongo script

Question

I want to pass the environment variable named file_path to js file.

I am using the following syntax:

mongo --eval "var file_path='$file_path'" < aggregation.js

Output:

MongoDB shell version: 3.2.9-rc0
connecting to: test

Note:

It does not execute aggregation.js file. only it pass the argument.

Answer 1

This worked for me:

mongo --eval "var my_var = '$MY_VAR'" my_script.js

Leave out the <. mongo will process any remaining arguments on the command line as files to be executed/interpreted, but apparently combining the shell input redirect with --eval causes the javascript namespace to be reset.

I assume but cannot confirm that this is because filenames passed as arguments are processed via the load() mechanism, which according to https://docs.mongodb.com/v3.2/reference/method/load/, behaves as follows:

After executing a file with load(), you may reference any functions or variables defined the file from the mongo shell environment.

Answer 2

According to this commit, it looks like there's a native method called _getEnv() that can do it for you.

const username = _getEnv('DB_USERNAME')
const password = _getEnv('DB_PASSWORD')
// use the username and password

Answer 3

Since Mongo 4.0.5 it is possible to utilize some of the new admin functions to load text files and execute programs. So you can write a Javascript function to execute a shell script that provides the value of an environment variable:

function getEnvValue(envVar, defVal) {
   var ret= run("sh", "-c", `printenv ${envVar} >/tmp/${envVar}.txt`);
   if (ret != 0) return defVal;
   return cat(`/tmp/${envVar}.txt`)
}

And then using it like this:

db.createCollection("myCol",
 { capped: true,
   size: getEnvValue('MYCOL_MAX_SIZE_GB', 2)*1024*1024*1024
});

This relies on the host shell but was acceptable in my case (Docker).

Was also trying to read the environ directly:

cat('/proc/self/environ').split('\0') # Doesn't work

but it only gets the first variable. I guess because of the null characters...

Answer 4

Looks like Native Method shellGetEnv() has been added meanwhile, see MongoDB GitHub

Function is available (thanks to @orgads):

_getEnv("PATH")

However, it is not documented and there is no statement yet whether it may be used by end-user or only as internal command.

The new MongoDB Shell, mongosh, is a fully functional JavaScript and Node.js 14.x REPL environment, thus you can access environment variables with process.env, e.g.

process.env["PATH"]

Answer 5

There's a suggestion from the mongo change request:

alias mongo="export | sed 's/declare -x /env./' > shell.js; mongo $@; rm shell.js;"

Then in ~/mongorc.js:

var env = {};
load('shell.js');

Answer 6

In case of Mongo 6 use process.env:

$ export A='a"a'
$ mongosh --quiet --eval 'console.log(process.env.A)'
a"a

Before 6.x:

$ q_A=`jq --arg v "$A" -n '$v'`
$ mongosh --quiet --eval "console.log($q_A)"
a"a

By the way, the mongo image (docker) comes with jq, although that might change.