Find an executable on the PATH

Before spawning a tool like git or ffmpeg, it is useful to know whether it is installed and where. This example implements the which command: scan each directory on the PATH for an executable file.

Edit on GitHub

async function which(command: string): Promise<string | null> {
  const PATH = Ende.env.get("PATH") ?? "";

Windows separates entries with ";" and resolves extensions from PATHEXT; this example covers the common case.

  const separator = Ende.build.os === "windows" ? ";" : ":";

  for (const dir of PATH.split(separator)) {
    if (dir === "")
      continue;

    const candidate = `${dir}/${command}`;

    try {
      const info = await Ende.stat(candidate);

On unix, check that some execute bit is set. Windows has no mode, so existence is the best cheap signal.

      const executable = Ende.build.os === "windows" ||
        ((info.mode ?? 0) & 0o111) !== 0;

      if (info.isFile && executable)
        return candidate;
    } catch {

Not in this directory; keep looking.

    }
  }

  return null;
}

console.log(await which("git")); // /usr/bin/git
console.log(await which("definitely-not-installed")); // null

A typical use is a friendly error before spawning a subprocess.

const ffmpeg = await which("ffmpeg");

if (!ffmpeg)
  console.log("ffmpeg is required: https://ffmpeg.org/download.html");

Reading the PATH requires -E, and stat-ing the candidates requires -R.

Run this example locally using the Ende CLI:

ende run -R -E https://docs.ende.sh/examples/scripts/find_executable.ts

Find an executable on the PATH

Additional resources