Environment variable permissions in Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of environment variable permissions in Deno?

Environment variable permissions in Deno control access to system environment variables, ensuring scripts only read variables when explicitly allowed, enhancing security.

beginner

How do you allow a Deno script to read a specific environment variable?

Use the flag --allow-env=VARIABLE_NAME when running the script, for example: deno run --allow-env=API_KEY script.ts allows reading only the API_KEY variable.

beginner

What happens if you try to access an environment variable without permission in Deno?

Deno throws a PermissionDenied error and prevents access to the environment variable to protect the system from unauthorized data exposure.

intermediate

How can you allow a Deno script to read all environment variables?

Use the flag --allow-env without specifying variable names, like deno run --allow-env script.ts, which grants access to all environment variables.

intermediate

Why is it safer to specify environment variable names instead of allowing all in Deno?

Specifying variable names limits exposure to only needed data, reducing risk if the script is compromised or shared, following the principle of least privilege.

Which flag allows a Deno script to read environment variables?

A --allow-net

B --allow-read

C --allow-env

D --allow-run

The --allow-env flag grants permission to access environment variables in Deno.

How do you allow access to only the environment variable named 'TOKEN'?

A --allow-env=TOKEN

B --allow-env

C --allow-env=ALL

D --allow-env=token

Using --allow-env=TOKEN grants access only to the 'TOKEN' variable. Variable names are case-sensitive.

What error occurs if a script tries to read an environment variable without permission?

A TypeError

B PermissionDenied

C ReferenceError

D SyntaxError

Deno throws a PermissionDenied error when environment variable access is blocked.

Which is the safest way to grant environment variable access in Deno?

A Allow variables only in development

B Allow all variables

C Never allow any variables

D Allow only specific variables needed

Allowing only specific variables follows the principle of least privilege and improves security.

What is the default behavior of Deno regarding environment variable access?

A No access unless explicitly allowed

B Full access by default

C Access only to variables starting with 'DENO_'

D Access only in interactive mode

Deno denies environment variable access by default to protect security.

Explain how environment variable permissions work in Deno and why they are important.

Think about how Deno protects your system from unauthorized data access.

Describe the difference between using --allow-env and --allow-env=VARIABLE_NAME in Deno.

Consider the principle of least privilege.

Practice

1. What does the --allow-env flag do in Deno?

easy

A. It encrypts environment variables.

B. It grants permission to access environment variables.

C. It sets environment variables automatically.

D. It disables environment variable access.

Solution

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

   This flag is used to allow a Deno program to read environment variables, which are otherwise blocked by default for security.

2. Step 2: Identify the correct description

   Among the options, only granting permission to access environment variables matches the flag's purpose.

3. Final Answer:

   It grants permission to access environment variables. -> Option B

4. Quick Check:

   Permission flag for env vars = D [OK]

Hint: Remember: --allow-env means allow environment access [OK]

Common Mistakes:

• Thinking it disables environment access
• Confusing it with setting variables
• Assuming it encrypts variables

2. Which of the following is the correct way to allow access only to the environment variable API_KEY in Deno?

easy

A. deno run --allow-env=API_KEY script.ts

B. deno run --allow-env API_KEY script.ts

C. deno run --allow-env API_KEY=script.ts

D. deno run --allow-env:API_KEY script.ts

Solution

1. Step 1: Recall the syntax for environment variable permission

   Deno uses --allow-env=VAR_NAME to allow access only to a specific variable.

2. Step 2: Match the correct syntax

   deno run --allow-env=API_KEY script.ts correctly uses --allow-env=API_KEY. Other options misuse spaces, equal signs, or colons.

3. Final Answer:

   deno run --allow-env=API_KEY script.ts -> Option A

4. Quick Check:

   Specific env var permission uses = [OK]

Hint: Use = to specify variable after --allow-env [OK]

Common Mistakes:

• Using space instead of = after --allow-env
• Adding extra characters like : or = in wrong places
• Confusing argument order

3. Given this command: deno run --allow-env=HOME script.ts and this code inside script.ts:

console.log(Deno.env.get("HOME"));
console.log(Deno.env.get("PATH"));

What will be the output?

medium

A. Prints undefined for both variables.

B. Prints HOME variable value, then prints PATH variable value.

C. Throws a permission error on accessing PATH.

D. Prints HOME variable value, then prints undefined.

Solution

1. Step 1: Understand permission scope

   The command allows access only to the HOME environment variable, not PATH.

2. Step 2: Predict output for each variable

   Accessing HOME prints its value. Accessing PATH returns undefined because permission is not granted.

3. Final Answer:

   Prints HOME variable value, then prints undefined. -> Option D

4. Quick Check:

   Allowed var prints value, others undefined [OK]

Hint: Only allowed env vars return values; others give undefined [OK]

Common Mistakes:

• Assuming all env vars print values
• Expecting a permission error instead of undefined
• Confusing variable names

4. You run deno run --allow-env=USER script.ts but inside script.ts you try to access Deno.env.get("HOME"). What will happen?

medium

A. It returns undefined without error.

B. It prints the HOME variable value.

C. It throws a runtime permission error.

D. It crashes the program.

Solution

1. Step 1: Check permission granted

   Only USER variable access is allowed, not HOME.

2. Step 2: Behavior when accessing disallowed env var

   Deno returns undefined for disallowed environment variables instead of throwing errors.

3. Final Answer:

   It returns undefined without error. -> Option A

4. Quick Check:

   Disallowed env vars return undefined, no error [OK]

Hint: Disallowed env vars return undefined, no crash [OK]

Common Mistakes:

• Expecting a permission error
• Thinking it prints the value anyway
• Assuming program crashes

5. You want to run a Deno script that needs access to API_KEY and DB_PASS environment variables only. Which command correctly grants minimal permissions?

hard

A. deno run --allow-env=API_KEY script.ts && deno run --allow-env=DB_PASS script.ts

B. deno run --allow-env script.ts

C. deno run --allow-env=API_KEY,DB_PASS script.ts

D. deno run --allow-env=API_KEY DB_PASS script.ts

Solution

1. Step 1: Understand how to specify multiple env vars

   Deno allows multiple variables by comma-separating them after --allow-env=.

2. Step 2: Evaluate each option

   deno run --allow-env=API_KEY,DB_PASS script.ts correctly uses comma separation. deno run --allow-env script.ts grants all env vars (too broad). deno run --allow-env=API_KEY script.ts && deno run --allow-env=DB_PASS script.ts runs script twice separately (inefficient). deno run --allow-env=API_KEY DB_PASS script.ts syntax is invalid.

3. Final Answer:

   deno run --allow-env=API_KEY,DB_PASS script.ts -> Option C

4. Quick Check:

   Multiple vars comma-separated after --allow-env= [OK]

Hint: Use commas to list multiple env vars after --allow-env= [OK]

Common Mistakes:

• Granting all env vars instead of specific ones
• Running script multiple times instead of once
• Using spaces instead of commas