denoland-deno/docs/getting_started/permissions.md

Permissions

Permissions whitelist

Deno also allows you to control the granularity of permissions with whitelists.

This example restricts file system access by whitelisting only the /usr directory:

$ deno run --allow-read=/usr https://deno.land/std/examples/cat.ts /etc/passwd
error: Uncaught PermissionDenied: read access to "/etc/passwd", run again with the --allow-read flag
► $deno$/dispatch_json.ts:40:11
    at DenoError ($deno$/errors.ts:20:5)
    ...

Try it out again with the correct permissions by whitelisting /etc instead:

$ deno run --allow-read=/etc https://deno.land/std/examples/cat.ts /etc/passwd

--allow-write works the same as --allow-read.

Network access:

fetch.ts:

const result = await fetch("https://deno.land/");

This is an example on how to whitelist hosts/urls:

$ deno run --allow-net=github.com,deno.land fetch.ts

Allow net calls to any host/url:

$ deno run --allow-net fetch.ts