Running with all permissions (--allow-all) in Deno - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What does the --allow-all flag do in Deno?

In Deno, what is the effect of running a script with the --allow-all flag?

A It grants the script permission to access all system resources without restrictions.

B It denies all permissions to the script, making it run in a sandbox.

C It only allows network access but denies file system access.

D It prompts the user for permission each time the script tries to access a resource.

💡 Hint

Think about what 'all permissions' means for a program.

The --allow-all flag in Deno grants the script full access to all permissions like file system, network, environment variables, and more, without any prompts or restrictions.

❓ component_behavior

intermediate

What happens if you run a Deno script without --allow-all and it tries to read a file?

Consider a Deno script that tries to read a file from the disk. What will happen if you run it without the --allow-all flag or any file read permission flags?

A The script will read the file successfully without any errors.

B The script will prompt the user to allow file read permission during execution.

C The script will ignore the file read and continue without error.

D The script will throw a permission error and stop execution.

💡 Hint

Deno is secure by default and restricts access unless explicitly allowed.

Without explicit permission flags like --allow-read or --allow-all, Deno denies file system access and throws a permission error.

📝 Syntax

advanced

Which command correctly runs a Deno script with all permissions?

You have a script named app.ts. Which command runs it with all permissions enabled?

A deno run app.ts --allow-all

B deno --allow-all run app.ts

C deno run --allow-all app.ts

D deno run app.ts --allow-all=true

💡 Hint

Remember the order of flags and arguments in Deno CLI commands.

The correct syntax places flags before the script name: deno run --allow-all app.ts. Options after the script name are treated as script arguments.

🔧 Debug

advanced

Why does this Deno script fail despite using --allow-all?

You run deno run --allow-all script.ts but the script throws a permission error when accessing environment variables. What is the likely cause?

Deno

console.log(Deno.env.get('HOME'));

A The script is run with --allow-all, so no permission error should occur; the error is from a typo.

B The environment variable access requires the --unstable flag in addition to --allow-all.

C The script was run with --allow-all, but environment variable access requires explicit --allow-env flag.

D The script was run with --allow-all, but environment variables are not accessible on this OS.

💡 Hint

Some Deno APIs are behind an unstable flag even with permissions.

Accessing environment variables requires permission and sometimes the --unstable flag if the API is unstable. Without --unstable, even with --allow-all, some APIs may fail.

❓ state_output

expert

What is the output of this Deno script run with --allow-all?

Given the script below, what will be printed when run with deno run --allow-all script.ts?

Deno

import { readTextFileSync } from "https://deno.land/std/fs/mod.ts";

try {
  const data = readTextFileSync("./data.txt");
  console.log(data.trim());
} catch {
  console.log("File not found");
}

A The content of data.txt with no extra spaces.

B "File not found" if data.txt does not exist.

C A runtime permission error because readTextFileSync requires --allow-read.

D An import error because the URL is invalid.

💡 Hint

Consider the effect of --allow-all on file system access and the try-catch block.

With --allow-all, the script can read files. If data.txt exists, its trimmed content prints. If not, the catch prints "File not found". The import URL is valid and no permission error occurs.

Practice

1. What does the --allow-all flag do when running a Deno script?

easy

A. Gives the script full access to all system permissions

B. Restricts the script from accessing the network

C. Only allows reading files but no writing

D. Runs the script without any permissions

Solution

1. Step 1: Understand the purpose of --allow-all

   This flag grants all permissions to the Deno script, including file, network, environment, and more.

2. Step 2: Compare with other permission flags

   Other flags restrict permissions, but --allow-all removes all restrictions for convenience.

3. Final Answer:

   Gives the script full access to all system permissions -> Option A

4. Quick Check:

   --allow-all = full permissions [OK]

Hint: Remember: --allow-all means no permission limits [OK]

Common Mistakes:

• Thinking it restricts permissions
• Confusing it with --allow-read only
• Assuming it disables permissions

2. Which of the following is the correct way to run a Deno script named app.ts with all permissions?

easy

A. deno run app.ts --allow-all

B. deno run --allow-all app.ts

C. deno --allow-all run app.ts

D. deno run app.ts --allow-read

Solution

1. Step 1: Recall Deno command syntax

   The correct order is: deno run [flags] script.ts. Flags come before the script name.

2. Step 2: Identify the correct flag placement

   deno run --allow-all app.ts places --allow-all before app.ts, which is correct syntax.

3. Final Answer:

   deno run --allow-all app.ts -> Option B

4. Quick Check:

   Flags come before script name [OK]

Hint: Put flags right after 'run' before script name [OK]

Common Mistakes:

• Placing flags after script name
• Using wrong flag like --allow-read
• Mixing command order

3. Consider this Deno script read_file.ts that reads a file and prints its content:

const data = await Deno.readTextFile("secret.txt");
console.log(data);

What will happen if you run deno run read_file.ts without any permission flags?

medium

A. The script will throw a permission error

B. The script will print the file content successfully

C. The script will run but print nothing

D. The script will crash with a syntax error

Solution

1. Step 1: Understand default permission behavior

   Deno denies file system access by default unless explicitly allowed.

2. Step 2: Analyze running without --allow-read or --allow-all

   Running without permissions causes a runtime permission error when trying to read files.

3. Final Answer:

   The script will throw a permission error -> Option A

4. Quick Check:

   No permission flags = permission error [OK]

Hint: No flags means no file access, expect permission error [OK]

Common Mistakes:

• Assuming script runs without errors
• Confusing permission error with syntax error
• Thinking script prints empty output

4. You run the command deno run --allow-net app.ts but your script also needs to read files. What is the best fix to avoid permission errors?

medium

A. Remove --allow-net flag

B. Change the script to not read files

C. Run the script without any flags

D. Add --allow-read flag or use --allow-all

Solution

1. Step 1: Identify missing permission

   The script needs file read permission, but only network permission is given.

2. Step 2: Fix by adding correct permission flags

   Add --allow-read or use --allow-all to grant all permissions and avoid errors.

3. Final Answer:

   Add --allow-read flag or use --allow-all -> Option D

4. Quick Check:

   Missing permission? Add it or use --allow-all [OK]

Hint: Add needed flags or use --allow-all for all permissions [OK]

Common Mistakes:

• Removing needed flags
• Running without flags expecting no errors
• Ignoring permission errors

5. You have a Deno script that needs to read files, write logs, access environment variables, and make network requests. Which command is the safest way to run it without permission errors but limiting unnecessary access?

hard

A. deno run --allow-all script.ts

B. deno run script.ts

C. deno run --allow-read --allow-write --allow-env --allow-net script.ts

D. deno run --allow-net script.ts

Solution

1. Step 1: Identify required permissions

   The script needs read, write, environment, and network permissions.

2. Step 2: Choose the command granting only needed permissions

   deno run --allow-read --allow-write --allow-env --allow-net script.ts grants exactly those permissions, avoiding full access.

3. Step 3: Understand why --allow-all is less safe

   deno run --allow-all script.ts grants all permissions, which is less secure than specifying only needed ones.

4. Final Answer:

   deno run --allow-read --allow-write --allow-env --allow-net script.ts -> Option C

5. Quick Check:

   Grant only needed permissions, not all [OK]

Hint: Grant only needed permissions, avoid --allow-all if possible [OK]

Common Mistakes:

• Using --allow-all without need
• Running without permissions
• Granting too few permissions causing errors