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=\'$fil         


        

Answer 1

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

So, would be simple

shellGetEnv("file_path")

However, the method is not documented and it looks it is not accessible from Mongo shell. Perhaps it becomes available in future releases.

Answer 2

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 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

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.