# Capturing Values
URL: /docs/workflow/concepts/capturing-values

Use readFile(path, as) to pull file contents out of the sandbox and into WorkflowResult.vars.



`SandboxBuilder` doesn't return `ExecHandle` — ops are queued, not executed. To get a value out of the sandbox, write it to a file inside the container and read it back with `readFile`.

## readFile [#readfile]

```ts
sb.exec("node --version > /tmp/ver.txt");
sb.readFile("/tmp/ver.txt", "nodeVersion");
```

After the workflow resolves, `vars.nodeVersion` contains the file's content as a string.

```ts
const { vars } = await workflow(client)
  .sandbox(opts, (sb) => {
    sb.exec("node --version > /tmp/ver.txt");
    sb.readFile("/tmp/ver.txt", "nodeVersion");
  })
  .result();

console.log(vars.nodeVersion); // "v22.x.x\n"
```

## Multiple values [#multiple-values]

Capture as many values as you need — each gets its own key:

```ts
const { vars } = await workflow(client)
  .sandbox(opts, (sb) => {
    sb.exec("node --version > /tmp/node.txt");
    sb.exec("npm --version > /tmp/npm.txt");
    sb.exec("uname -r > /tmp/kernel.txt");
    sb.readFile("/tmp/node.txt", "node");
    sb.readFile("/tmp/npm.txt", "npm");
    sb.readFile("/tmp/kernel.txt", "kernel");
  })
  .result();

console.log(vars); // { node: "v22.x.x\n", npm: "10.x.x\n", kernel: "..." }
```

## Passing values between sequence steps [#passing-values-between-sequence-steps]

`readFile` values are available in the next step via `prev.vars`:

```ts
await workflow(client)
  .sequence([
    {
      image: "node:22",
      resources: opts.resources,
      run: (sb) => {
        sb.exec("npm run build:version > /tmp/version.txt");
        sb.readFile("/tmp/version.txt", "version");
      },
    },
    {
      image: "ubuntu:22.04",
      resources: opts.resources,
      run: (sb, prev) => {
        const version = String(prev.vars.version).trim();
        sb.exec(`./deploy.sh --version ${version}`);
      },
    },
  ])
  .pipe(process.stdout);
```

## stdout [#stdout]

The combined stdout from all exec calls is also available in `WorkflowResult.stdout`. For selective capture, `readFile` is more reliable than parsing stdout.

```ts
const { stdout } = await workflow(client)
  .sandbox(opts, (sb) => {
    sb.exec("npm test");
  })
  .result();
```