Wildcards in child_process spawn()?

Question

I want to execute a command like "doSomething ./myfiles/*.csv" with spawn in node.js. I want to use spawn instead of exec, because it is some kind of watch process and I need the stdout output.

I tried this

var spawn = require('child_process').spawn; 
spawn("doSomething", ["./myfiles/*.csv"]);

But then the wildcard *.csv will not interpreted.

Is it not possible to use wildcards when using spawn()? Are there other possibilities to solve this problem?

Thanks

Torben

Answer 1

The * is being expanded by the shell, and for child_process.spawn the arguments are coming through as strings so will never get properly expanded. It's a limitation of spawn. You could try child_process.exec instead, it will allow the shell to expand any wildcards properly:

var exec = require("child_process").exec;

var child = exec("doSomething ./myfiles/*.csv",function (err,stdout,stderr) {
    // Handle result
});

If you really need to use spawn for some reason perhaps you could consider expanding the wildcard file pattern yourself in Node with a lib like node-glob before creating the child process?

Update

In the Joyent Node core code we can observe an approach for invoking an arbitrary command in a shell via spawn while retaining full shell wildcard expansion:

https://github.com/joyent/node/blob/937e2e351b2450cf1e9c4d8b3e1a4e2a2def58bb/lib/child_process.js#L589

And here's some pseudo code:

var child;
var cmd = "doSomething ./myfiles/*.csv";

if ('win32' === process.platform) {
    child = spawn('cmd.exe', ['/s', '/c', '"' + cmd + '"'],{windowsVerbatimArguments:true} );
} else {
    child = spawn('/bin/sh', ['-c', cmd]);
}

Answer 2

Here's the simplest solution:

spawn("doSomething", ["./myfiles/*.csv"], { shell: true });

As @JamieBirch suggested in his comment, the key is telling spawn() to use the shell ({ shell: true }, see the docs), so the wildcard is properly resolved.