How to pipe shell commands in NodeJS

how-to-pipe.js

// In this example, we use ChildProcess and piping to perform the NodeJS
// version of `find ~/Documents | egrep '\.ts$'`

const ChildProcess = require(“child_process”);

// 1. Start both "find" and "egrep"
// "shell" has to be true, so that we have access to "~"
const find = ChildProcess.spawn("find", ["~/Documents"], { shell: true });
const egrep = ChildProcess.spawn("egrep", ["\\.ts$"], {
  shell: true
});

// 2. Pipe the output of "find" into "egrep"'s input
find.stdout.pipe(egrep.stdin);

// 3. Once "find" has finished outputting results, we need to notify "egrep"
// that there's no more input. If we don't do this, egrep will hang forever
// waiting for the end of its input
find.stdout.once("end", () => {
  egrep.stdin.end();
});

// 4. Pipe "egrep" to console output
egrep.stdout.pipe(process.stdout);

// 5. Once "egrep" finishes, we terminate our program
egrep.once("exit", exitCode => {
  process.exit(exitCode === null ? undefined : exitCode);
});

// 6. If there are any errors, surface them to the user
find.on("error", err => {
  throw err;
});
egrep.on("error", err => {
  throw err;
});