child_process.exec() stdout is empty string when command contains spaces - node.js

Question

I have put the below code in a Javascript file and ran it using node.
var exec = require('child_process').exec;
var child;
child = exec("git for-each-ref --format='%(committerdate), %(authorname)' --sort=committerdate --merged develop",
function (error, stdout, stderr) {
console.log('stdout: ' + stdout);
console.log('typeof stdout: ' + typeof stdout);
console.log('stderr: ' + stderr);
if (error !== null) {
console.log('exec error: ' + error);
}
});
All I get is an empty string as stdout. There are no errors.
stdout:
stderr:
However, if I remove the space after comma in "%(committerdate), %(authorname)", I get the expected output. The below code works:-
var exec = require('child_process').exec;
var child;
child = exec("git for-each-ref --format='%(committerdate),%(authorname)' --sort=committerdate --merged develop",
function (error, stdout, stderr) {
console.log('stdout: ' + stdout);
console.log('stderr: ' + stderr);
if (error !== null) {
console.log('exec error: ' + error);
}
});
Why do I not get any output when there is a space after comma?
When I run the command directly on in PowerShell or git-bash, I get the same output with and without the space.
git for-each-ref --format='%(committerdate), %(authorname)' --sort=committerdate --merged develop
I spent quite some time to get the command working and it seemed to be that a space would cause an issue, especially when the command works fine when run directly.
Environment:
Windows 10
Node 16.7.0

Answer 1

It's probably worth putting into an answer to give people ideas on how to troubleshoot.
Let's look at the command first:
exec("git for-each-ref --format='%(committerdate), %(authorname)' --sort=committerdate --merged develop", ...);
If we wanted to look at the underbelly of the exec function, we would probably find a more sophisticated version of inputString.split(" ") so that node can distinguish the executable from the positional arguments/flags. So a good place to start is to try and escape the space in various ways to see if that works.
Next you need to understand how node executes the command. On different operating systems, the node child_process library is just a proxy to an underlying shell. So you need to make sure your command works in the target shell (which is likely not your favorite shell or the one you use on a day-to-day basis). For Windows, node likely uses cmd.exe under the hood.
Lastly, the child_process library also allows you to spawn a process which is a little more deliberate in specifying the executable and positional arguments/flags. I recommend using this method for most child_process operations:
spawn(<executable>, [...<args>]);
This way you are telling node exactly what binary to use while clearly identifying every positional argument. For example, the following will fail:
spawn('git', ['checkout -b my-new-branch']);
The reason this fails is because node treats the string 'checkout -b my-new-branch' as a single argument to the git command... which is not correct. Instead, you want to clearly define each positional argument separately:
spawn('git', ['checkout', '-b', 'my-new-branch']);
This is particularly useful if one of your arguments contains spaces or other special shell characters:
spawn('git', ['checkout', '--format=\'%(committerdate), %(authorname)\'', '--sort=committerdate', '--merged develop']);
Changing the underlying shell
For any of the child_process creation methods, you can pass an option for which shell to use. Be careful using this option because you can destroy the ability for your code to run on multiple operating systems. Make sure to read about shell requirements and the default windows shell:
exec("...", { shell: "powershell.exe" });
spawn("...", [...], { shell: "powershell.exe" });