How do I escape a string for a shell command in node?

Question

How do I escape a string for a shell command in node?

In nodejs, the only way to execute external commands is via sys.exec(cmd). I'd like to call an external command and give it data via stdin. In nodejs there does yet not appear to be a way to open a command and then push data to it (only to exec and receive its standard+error outputs), so it appears the only way I've got to do this right now is via a single string command such as:

var dangerStr = "bad stuff here";
sys.exec("echo '" + dangerStr + "' | somecommand");

Most answers to questions like this have focused on either regex which doesn't work for me in nodejs (which uses Google's V8 Javascript engine) or native features from other languages like Python.

I'd like to escape dangerStr so that it's safe to compose an exec string like the one above. If it helps, dangerStr will contain JSON data.

javascript
shell
escaping
node.js
v8

Answer 1

This is what I use:

var escapeShell = function(cmd) {
  return '"'+cmd.replace(/(["\s'$`\\])/g,'\\$1')+'"';
};

Answer 2

There is a way to write to an external command: process.createChildProcess (documentation) returns an object with a write method. createChildProcess isn't as convenient though, because it doesn't buffer stdout and stderr, so you will need event handlers to read the output in chunks.

var stdout = "", stderr = "";
var child = process.createChildProcess("someCommand");

child.addListener("output", function (data) {
    if (data !== null) {
        stdout += data;
    }
});
child.addListener("error", function (data) {
    if (data !== null) {
        stderr += data;
    }
});
child.addListener("exit", function (code) {
    if (code === 0) {
        sys.puts(stdout);
    }
    else {
        // error
    }
});

child.write("This goes to someCommand's stdin.");

Answer 3

If you need simple solution you can use this:

function escapeShellArg (cmd) {
    return '\'' + cmd.replace(/\'/g, "'\\''") + '\'';
}

So your string will be simply escaped with single quotes as Chris Johnsen mentioned.

echo 'John'\''s phone';

But actually nodejs escaping it for you:

var child = require('child_process')
  .spawn('echo', ['`echo 1`;"echo $SSH_TTY;\'\\0{0..5}']);

child.stdout.on('data', function (data) {
  console.log('stdout: ' + data);
});

child.stderr.on('data', function (data) {
  console.log('stderr: ' + data);
});

Will execute:

echo '`echo 1`;"echo $SSH_TTY;'\''\\0{0..5}'

And output:

stdout: `echo 1`;"echo $SSH_TTY;\'\\0{0..5}

Or some error.

Take a look at http://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options

By the way simple solution to run a bunch of commands is:

require('child_process')
  .spawn('sh', ['-c', [
    'cd all/your/commands',
    'ls here',
    'echo "and even" > more'
  ].join('; ')]);

Have a nice day!