git-output-handler.md

Output Handler

As simple-git receives data on either stdout or stderr streams from the git child processes it spawns, the data is buffered for parsing when the process has completed.

Add an outputHandler to the instance to pipe these streams to another target, for example piping to the main process stdout / stderr:

import { InitResult, SimpleGit, simpleGit } from "simple-git";

const git: SimpleGit = simpleGit()
   .outputHandler((_command, stdout, stderr) => {
      stdout.pipe(process.stdout);
      stderr.pipe(process.stderr);
   });

const init: InitResult = await git.init();

Note: there is a single outputHandler per simple-git instance, calling the method again will overwrite the existing outputHandler.

Other uses for the outputHandler can include tracking the processes for metrics purposes, such as checking how many commands are currently being executed:

let processes = new Set();
const currentlyRunning = () => processes.size;
const git = context.git.outputHandler((_command, stdout, stderr) => {
   const start = new Date();
   const onClose = () => processes.delete(start);

   stdout.on('close', onClose);
   stderr.on('close', onClose);

   processes.add(start);
});

expect(currentlyRunning()).toBe(0);
const queue = [git.init(), git.add('*.txt')];

await wait(0);
expect(currentlyRunning()).toBe(2);

await Promise.all(queue);
expect(currentlyRunning()).toBe(0);