Running with all permissions (--allow-all) in Deno - Step-by-Step Execution

Concept Flow - Running with all permissions (--allow-all)

Start Deno Script

↓

Check Permissions

↓

--allow-all Flag Present?

No→Block Restricted Actions

Yes↓

Grant All Permissions

↓

Execute Script Fully

↓

End Script

This flow shows how Deno checks permissions before running a script. If --allow-all is used, all permissions are granted and the script runs without restrictions.

Execution Sample

Deno

deno run --allow-all script.ts

console.log("File read and network access allowed.");

Runs a Deno script with all permissions granted, allowing file and network access.

Execution Table

Step	Action	Permission Check	Result	Script Behavior
1	Start script execution	No check yet	Waiting for permission check	No output
2	Detect --allow-all flag	All permissions granted	Permission granted	Script can access files, network, environment, etc.
3	Run script code	Permissions allowed	Access successful	Console logs message
4	Script finishes	No further checks	Execution ends	Program ends normally

💡 Script ends after running with all permissions granted by --allow-all flag

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
permissions	none	all granted	all granted	all granted
script_access	none	allowed	allowed	allowed
output	none	none	"File read and network access allowed."	"File read and network access allowed."

Key Moments - 2 Insights

Why does the script run without permission errors when using --allow-all?

Because the --allow-all flag grants every permission before the script runs, as shown in step 2 of the execution table.

What happens if --allow-all is not used?

Deno blocks actions that require permissions not explicitly granted, causing errors or denied access, unlike the granted state in step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the permission state at step 2?

A Only network permission granted

B No permissions granted

C All permissions granted

D Only file read permission granted

💡 Hint

Check the 'Permission Check' column at step 2 in the execution table.

At which step does the script output the console message?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Script Behavior' column for when the console logs the message.

If the --allow-all flag was removed, how would the 'permissions' variable change after step 2?

A It would be 'none' or limited

B It would remain 'all granted'

C It would be 'network only'

D It would be 'file only'

💡 Hint

Refer to the 'permissions' row in variable_tracker and the explanation in key_moments.

Concept Snapshot

Deno runs scripts with strict permissions by default.
Using --allow-all grants every permission.
This lets scripts access files, network, environment, and more.
Without it, Deno blocks unauthorized actions.
Use --allow-all carefully for trusted scripts.

Full Transcript

When you run a Deno script, it checks what permissions it has. Normally, it blocks actions like reading files or accessing the network unless you allow them. If you run the script with the --allow-all flag, Deno gives the script every permission it needs. This means the script can do anything without being stopped. The execution table shows that at step 2, all permissions are granted, so the script runs fully and prints its message. If you don't use --allow-all, the script might get blocked when trying to do restricted actions. So, --allow-all is a quick way to let your script run without permission errors, but only use it when you trust the code.

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