Reading application stdout data using node.js -

let's take e.g. "top" application displays system information , periodically updates it.

i want run using node.js , display information (and updates!). code i've come with:

#!/usr/bin/env node  var spawn = require('child_process').spawn;  var top = spawn('top', []);  top.stdout.on('readable', function () {     console.log("readable");     console.log('stdout: '+top.stdout.read()); }); 

it doesn't behave way expected. in fact produces nothing:

readable stdout: null readable stdout: readable stdout: null 

and exits (that unexpected).

top application taken example. goal proxy updates through node , display them on screen (so same way running top directly command line).

my initial goal write script send file using scp. done , noticed missing progress information scp displays. looked around @ scp node modules , not proxy it. backtracked common application top.

top interactive console program designed run against live pseudo-terminal.

as stdout reads, top seeing stdin not tty , exiting error, no output on stdout. can see happen in shell if echo | top exit because stdin not tty.

even if running though, it's output data going contain control characters manipulating fixed-dimension console. (like "move cursor beginning of line 2"). interactive user interface , poor choice programmatic data source. "screen scraping" , interpreting data , extracting meaningful information going quite difficult , fragile. have considered cleaner approach such getting data need out of /proc/meminfo file , other special files kernel exposes purpose? top getting data readily-available special files , system calls, should able tap data sources convenient programmatic access instead of trying screen scrape top.

now of course, top has analytics code averages , forth may have re-implement, both screen-scraping , going through clean data sources have pros , cons, , aspects easy , difficult. $0.02 focus on data sources instead of trying screen scrape console ui.

other options/resources consider:

• the free command such free -m
• vmstat
• and other commands described in article
• the expect program designed automate console programs expect terminal

and clear, yes possible run top child process, trick thinking there's tty , associated environment settings, , @ data writing. it's extremely complicated , analogous trying weather taking photo of weather channel on tv screen , running optical character recognition on it. points style, there easier ways. expect command if need research more tricking console programs running subprocesses.