NodeJS get output from child_process with command df -h on raspi

Question

I'm using Raspberry Pi with nodeJS to do child_process.

On shell command, I do:

df -h

and the output is:

Sistem Berkas  Besar   Isi  Sisa Isi% Dipasang di
/dev/root        58G  5,1G   50G  10% /
devtmpfs        460M     0  460M   0% /dev
tmpfs           464M  8,3M  456M   2% /dev/shm
tmpfs           464M   13M  452M   3% /run
tmpfs           5,0M  4,0K  5,0M   1% /run/lock
tmpfs           464M     0  464M   0% /sys/fs/cgroup
/dev/mmcblk0p1   44M   23M   22M  51% /boot
tmpfs            93M     0   93M   0% /run/user/1000
/dev/sda1       7,5G  2,0G  5,6G  27% /media/pi/USB DISK

Then now I do on nodeJS script.

var exec = require('child_process').exec;

function execute(command, callback) {
  var cmd = exec(command, function(error, stdout, stderr) {
    console.log("error: " + error);
    callback(stdout);
  });
}

exec('df -h',(error,stdout,stderr) => {
  if(error){
    console.error( `exec error: ${error}` );
    return;
  }

  var abc = [];
  abc = stdout;

  res.json(abc);
});

My question, how can I get specific of the output? Example I just want to get at row 1, it's 50G

Answer 1

stdout is a string, so you can split it and then you can grab whichever rows you want. Example:

const { exec } = require('child_process')

exec('df -h', (error, stdout) => {
  if (error) {
    console.error(`exec error: ${error}`)
    return
  }

  // split stdout on newlines, and filter to remove the ending empty string
  const lines = stdout.split('\n').filter(Boolean)

  // entry 0 will be the headers, we want the first non-header line
  console.log(lines[1])
})

If you want to make that dynamic, you can use a function:

const getRowForDevice = (rows, device) =>
  rows.filter((x) => x.startsWith(device))[0]

// rest of exec callback
  console.log(getRowForDevice(lines, '/dev/root'))

Since the size is the second column, you can get just the size with another split and filter:

  const lineWeWant = lines[0] // or try the function above
  // split the string again, filter out empty strings, and then take the second entry
  const sizeForDevice = lineWeWant.split(' ').filter(Boolean)[1]

And as a sidenote there's also this excellent package which might be easier than dealing with df and child_process .