Can not getting complete stdout using node.js

Question

i am using following code in my app:

var path = app.getAppPath();
var spawn = require('child_process').spawn;
const child = exec(`"${path}\\PC-BASIC\\a.bat"`, []);
var stdout = '';
var stderr = '';
child.stdout.on('data', function(buf) {
  //console.log('[STR] stdout "%s"', String(buf));
  stdout += buf;
});
child.stderr.on('data', function(buf) {
  //console.log('[STR] stderr "%s"', String(buf));
  stderr += buf;
});
child.on('close', function(code) {
  console.log('[END] code', code);
  console.log('[END] stdout "%s"', stdout);
  console.log('[END] stderr "%s"', stderr);
});

when i run a.bat from command line (dos). i get the exact result. but when i run it from my electron app i writes following on console:

 [END] code 0
 [END] stdout "
 D:\Documents\Nauman Umer\New folder\electron-quick-start>"C:\Program Files (x86)\PC-BASIC\pcbasic.com" --load="ART.BAS" --convert=A
 "
 [END] stderr ""

but expected is:

 [END] code 0
 [END] stdout "
 D:\Documents\Nauman Umer\New folder\electron-quick-start>"C:\Program Files (x86)\PC-BASIC\pcbasic.com" --load="ART.BAS" --convert=A
 [FILE TEXT AS IN OUTPUT OF BAT]
 "
 [END] stderr ""

i also tried to execute pcbasic directly from command line instead of from app but the results are same.

Are you sure the program prints to stdout. Not all programs on Windows print to stdout. Some directly call the console API to print their output. — slebetman
– slebetman, Commented Sep 26, 2016 at 17:11
its an python program and using sys.stdout.write() for writing to console. — Nauman Umer
– Nauman Umer, Commented Sep 27, 2016 at 15:55

jochietoch · Accepted Answer · 2016-09-27 12:40:55Z

1

If the child process uses GetConsoleMode to detect whether it runs in a console, try calling it using spawn() rather than exec() in line 3 of your code.

child_process.exec() launches a console, and then launches the program inside that console - so the child process called by a.bat sees a console and may use the console API, as suggested by @slebetman .

child_process.spawn() launches the program directly and makes its stdout available through a pipe, so the child process should not see a console (and cannot use the console API).

See here for details: https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options

answered Sep 27, 2016 at 12:40

jochietoch

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2 Comments

Nauman Umer Over a year ago

I am using this code

const spawn = require('child_process').spawn;   const ls = spawn("D:\\Documents\\Nauman Umer\\New folder\\electron-quick-start\\PC-BASIC\\a.bat", []);    ls.stdout.on('data', (data) => {     console.log(`stdout: ${data}`);   });    ls.stderr.on('data', (data) => {     console.log(`stderr: ${data}`);   });    ls.on('close', (code) => {     console.log(`child process exited with code ${code}`);   });

but note getting any thing

Nauman Umer Over a year ago

the output is

stdout: D:\Documents\Nauman Umer\New folder\electron-quick-start>"D:\Documents\Nauman Umer\New folder\electron-quick-start\PC-BASIC\pcbasic.com" --load="ART.BAS" --convert=A  child process exited with code 0

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