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node.jslinuxgulp

How to access shell variable value from Node.js?

Let's say there is a variable key1 and its value is 123

key1=123

so when I run the command in linux environment echo $key1, I get output as 123.

enter image description here

Now I have the following gulp task.

const child_process = require('child_process');
....
gulp.task('printKeyValue', function() {
    var value1 = child_process.execSync('echo $key1');
    console.log(value1.toString().trim());
});

Here, I'm trying to access value of linux variable from nodejs by using Child Process

But when I run the following gulp task, I don't get the desired output.

npm run gulp -- printKeyValue

Instead I get output as $key1 and not 123.

See below screenshot

enter image description here

Other commands like ls & pwd in gulp task gives the desired output.

Can some one please help on this or suggest an alternate way?

Solution

  • You are not exporting the variable. When you just do

    key1=123

    the variable is not propagated to subprocesses. It will be available in your current bash process, so you can see it when you type echo $key1, but it will not get inherited by the node process. As man bash says:

    When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless otherwise noted, the values are inherited from the shell.

    • [...]

    • shell variables and functions marked for export, along with variables exported for the command, passed in the environment

    You need to either define the variable as exported

    export key1=123

    or mark an existing variable for export

    key1=123
export key1

    or launch your node with the modified environment, either via the bash innate capability to do so

    key1=123 node code.js

    or using /usr/bin/env utility:

    env key1=123 node code.js

    Once the variable is properly passed to the node process, it will be available both in process.env.key1 and as $key1 in a child process.

    EDIT: I just noticed, you actually gave the command you're running; it does not matter, the same logic goes for every executable, whether node or npm or anything else.