I am using the readline module to create a mand line interface (CLI) for an application in Node.js.

The problem is that I can not scroll up to view the past mands as I usually can in Terminal. My CLI is just a fixed window and if I print too much out to the screen, I lose information at the top and there is no way to scroll up to see it.

(I am running my program on Mac OSX Mavericks)

Thanks in advance.

Code Snippet:

var readline = require('readline');

var Cli = function () {
    this.txtI = process.stdin;
    this.txtO = process.stdout;

    process.stdout.write('CLI initialized.');

    this.rl = readline.createInterface({input: this.txtI, output: this.txtO });
    this.rl.setPrompt('>>>');
    this.rl.prompt();
    this.rl.on('line', function(line) {
        var input = line.toString().trim();
        if (input) {
            this.txtO.write('cmd: ' + input);
        }
        this.rl.prompt();
    }.bind(this)).on('close', function() {
        this.txtO.write('Have a great day!');
        process.exit(0);
    }.bind(this));
};

new Cli();

Save this file as snippet.js and run

node snippet.js

in terminal.

I am using the readline module to create a mand line interface (CLI) for an application in Node.js.

The problem is that I can not scroll up to view the past mands as I usually can in Terminal. My CLI is just a fixed window and if I print too much out to the screen, I lose information at the top and there is no way to scroll up to see it.

(I am running my program on Mac OSX Mavericks)

Thanks in advance.

Code Snippet:

var readline = require('readline');

var Cli = function () {
    this.txtI = process.stdin;
    this.txtO = process.stdout;

    process.stdout.write('CLI initialized.');

    this.rl = readline.createInterface({input: this.txtI, output: this.txtO });
    this.rl.setPrompt('>>>');
    this.rl.prompt();
    this.rl.on('line', function(line) {
        var input = line.toString().trim();
        if (input) {
            this.txtO.write('cmd: ' + input);
        }
        this.rl.prompt();
    }.bind(this)).on('close', function() {
        this.txtO.write('Have a great day!');
        process.exit(0);
    }.bind(this));
};

new Cli();

Save this file as snippet.js and run

node snippet.js

in terminal.

• javascript
• node.js
• mand-line-interface
• readline

Share Improve this question Follow edited Nov 21, 2013 at 20:53 rustybeanstalk asked Nov 20, 2013 at 3:01 rustybeanstalkrustybeanstalk 2,7621010 gold badges3939 silver badges5757 bronze badges 5

• You want to show past mands how? When you press the UP arrow key for example? If so, that's something you'd have to implement. – WiredPrairie Commented Nov 20, 2013 at 3:55
• Could you post how you use readline in your node script? – Jeff Sisson Commented Nov 20, 2013 at 4:14
• I've added a distilled version of my CLI. I seem to have fixed my scrolling problem with this code. I do have another problem. I can not seem to write to the process.stdout stream. Any help with that? – rustybeanstalk Commented Nov 20, 2013 at 23:30
• Why are you cacheing the process.stdout with the this.txtO variable? Why not just use / reference process.stdout directly? – Jeff Sisson Commented Nov 21, 2013 at 4:16
• I would like to use any streams, not just process.stdin, and process.stdout. I could pipe any stream into txtI and pipe txtO to any stream. – rustybeanstalk Commented Nov 21, 2013 at 20:51

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2 Answers 2

Sorted by: Reset to default 4

It probably is working, just readline is overwriting your line. Try outputting multiple lines:

process.stdout.write("1\n2\n3\n4\n5");

Readline is quite an awesome module. History is already there. As is the possibility to add pletion. Try the snippet below.

var readline = require('readline');

function createCLI(opt) {

    var rl = readline.createInterface({
          input : opt.input,
         output : opt.output,
       terminal : opt.terminal || true,
      pleter : opt.pleter ||
        function asyncCompleter(linePartial, callback){
          var pletion = linePartial.split(/[ ]+/);
          callback(null, [pletion, linePartial]);
        }
    });

    rl.on('line', function(line) {
      if( !line.trim() ){  this.prompt();  }
      else { this.write(line); }
    }).on('close', function() {
      this.output.write('\n Have a great day!');
      process.exit(0);
    }).setPrompt(' > ');

    rl.output.write(' CLI initialized\n');
    return rl;
}

var cli = createCLI({
   input : process.stdin,
  output : process.stdout
});

cli.prompt();