How do I run a system command from an ionic3 app?

Question

• What? I would like to run a command from app running in Chromium on Linux (or potentially Windows or Android in the future)
• Why? to control for example some audio/TV equipment like via cec-client eg.

echo "tx 20:36" | cec-client RPI -s -d 4

• however the question around concept of shelling, spawning commands is generic.

I have put together the following SystemCall class which contains several attempts from different posts I found however I am stuck on this error "Cannot find module "child_process"

• I understand you are not supposed to run system calls from JS/TS however this app will run in a controlled environment.
• Hopefully I will not need a local server or php but if you think you have a solution I will certainly consider. I need to make a call against the local hardware not on a remote server.
• I am stuck at Ionic3 too many breaking changes to move to Ionic5.

// 
//----------------------------------------------------------------------
// FRAMEWORKS IMPORTS
//----------------------------------------------------------------------
import { Injectable } from '@angular/core' // 20160731
//
import { exec, ChildProcess, execSync} from 'child_process'
// import * as child from 'child_process';
//
//
//----------------------------------------------------------------------
// JS LIBRARY
//----------------------------------------------------------------------
// declare var plyr: any; // Magic makes JS variable available to TS :)
// declare var execSync 
//
/** - 20200607 */
@Injectable()
export class SystemCall {

    constructor(
        public ChildProcess: ChildProcess,

    ) {

    }

    Run() {
        this.Shell('notepad.exe')
        // this.Run1()
    }

    // https://stackoverflow.com/questions/5321884/how-do-i-run-the-system-commands-in-javascript
    Run0() {
        var spawn = require('child_process').spawn
        var Run = spawn('ls', ['-l']);
        // let Run = spawn('notepad.exe', [])
        Run.stdout.on('data', function (data) {
            console.log(data);
        });
    }

    Run1() {
        const { exec } = require("child_process");

        exec("dir", (error, stdout, stderr) => {
            if (error) {
                console.log(`error: ${error.message}`);
                return;
            }
            if (stderr) {
                console.log(`stderr: ${stderr}`);
                return;
            }
            console.log(`stdout: ${stdout}`);
        });
    }


    // https://stackoverflow.com/questions/1880198/how-to-execute-shell-command-in-javascript/52575123#52575123
    Run3() {
        const execSync = require('child_process').execSync;
        // import { execSync } from 'child_process';  // replace ^ if using ES modules
        const output = execSync('notepad.exe', { encoding: 'utf-8' });  // the default is 'buffer'
        console.log('Output was:\n', output);
    }

    // https://stackoverflow.com/questions/36546860/require-nodejs-child-process-with-typescript-systemjs-and-electron
    Run4() {
        // var foo: child.ChildProcess = child.exec('notepad.exe');
        // console.log(typeof foo.on);
    }

    // https://stackoverflow.com/questions/1880198/how-to-execute-shell-command-in-javascript/31897900#31897900
    /**
     * Execute simple shell command (async wrapper).
     * @param {String} cmd
     * @return {Object} { stdout: String, stderr: String }
     */
    async Shell(cmd) {
        return new Promise(function (resolve, reject) {
            exec(cmd, (err, stdout, stderr) => {
                if (err) {
                    reject(err);
                } else {
                    resolve({ stdout, stderr });
                }
            });
        });
    }

    async  Run5() {
        let stdout = await this.Shell('cmd.exe /c dir')
        for (let line of stdout.toString().split('\n')) {
            console.log(`ls: ${line}`);
        }
    }

}

I am currently injecting SystemCall into app.component.ts and calling SystemCall.Run() to test out.

What's strange is that VSCode reveals the signatures of exec, etc.. when I hover with the mouse over the import line??

I have run the command

npm install child_process --save

my packages now shows

Thanks for helping out, right now I am swimming in murky waters.

Answer 1

You cannot run system calls just like that in a hybrid client app, since the code is executed in a web view.

It may be possible using a Cordova plugin, such as cordova-plugin-shell-exec .