API interaction scripts in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an API in the context of scripting?

An API (Application Programming Interface) is a way for programs to talk to each other. In scripting, it lets your script send requests to a service and get data back.

beginner

Which command is commonly used in bash scripts to interact with APIs?

The curl command is commonly used to send HTTP requests to APIs from bash scripts.

intermediate

How do you include headers like API keys in a curl request?

Use the -H option with curl. For example: curl -H "Authorization: Bearer YOUR_API_KEY" URL

beginner

What does the -X POST option do in a curl command?

It tells curl to send a POST request instead of the default GET request. POST is used to send data to the API.

intermediate

Why is it useful to parse API responses in bash scripts?

Parsing API responses lets your script understand the data returned, so it can make decisions or show useful info. Tools like jq help extract data from JSON responses.

Which command sends a GET request to an API in bash?

A curl https://api.example.com/data

B curl -X POST https://api.example.com/data

C curl -d '{"key":"value"}' https://api.example.com/data

D curl -H 'Content-Type: application/json' https://api.example.com/data

By default, curl sends a GET request. Option A is a simple GET request.

How do you add a header for an API key in a curl request?

A curl -H 'Authorization: Bearer YOUR_API_KEY' URL

B curl -X GET YOUR_API_KEY URL

C curl --api-key YOUR_API_KEY URL

D curl -d 'Authorization=YOUR_API_KEY' URL

Headers are added with -H option. Authorization header is common for API keys.

What tool helps parse JSON responses in bash scripts?

A sed

B grep

C awk

D jq

jq is designed to parse and filter JSON data easily.

Which HTTP method is used to send data to an API?

A GET

B DELETE

C POST

D HEAD

POST is used to send data to an API, often to create or update resources.

What does the -d option do in a curl command?

A Deletes data from the server

B Adds data to send in the request body

C Displays detailed output

D Downloads a file

-d sends data in the request body, usually with POST requests.

Explain how you would write a bash script to get data from an API that requires an API key.

Think about how to include the API key in the request headers.

Describe how to handle and extract useful information from a JSON API response in a bash script.

Consider tools that help read JSON in bash.

Practice

1. What is the primary tool used in bash scripts to interact with web APIs?

easy

A. sed

B. grep

C. awk

D. curl

Solution

1. Step 1: Understand the purpose of each tool

   curl is used to send HTTP requests, while grep, awk, and sed are text processing tools.

2. Step 2: Identify the tool for API interaction

   Since APIs communicate over HTTP, curl is the correct tool to send requests and receive responses.

3. Final Answer:

   curl -> Option D

4. Quick Check:

   API calls use curl [OK]

Hint: Remember: curl sends web requests in bash [OK]

Common Mistakes:

• Confusing text tools like grep with API tools
• Using sed or awk for HTTP requests
• Thinking bash has a built-in HTTP client

2. Which of the following is the correct syntax to send a GET request to https://api.example.com/data using curl?

easy

A. curl https://api.example.com/data

B. curl --data https://api.example.com/data

C. curl -d https://api.example.com/data

D. curl -X POST https://api.example.com/data

Solution

1. Step 1: Understand default curl behavior

   By default, curl sends a GET request if no method is specified.

2. Step 2: Analyze options

   curl https://api.example.com/data sends a GET request simply by specifying the URL. The other options either specify POST or data, which changes the method.

3. Final Answer:

   curl https://api.example.com/data -> Option A

4. Quick Check:

   Default curl = GET request [OK]

Hint: No method means GET by default in curl [OK]

Common Mistakes:

• Using -X POST when GET is needed
• Adding -d or --data without POST method
• Confusing GET and POST syntax

3. What will be the output of this script snippet?

response=$(curl -s -H "Accept: application/json" https://api.example.com/status)
echo "$response"

medium

A. An error message about missing POST data

B. The raw JSON response from the API

C. Nothing, because the script has a syntax error

D. The HTTP status code only

Solution

1. Step 1: Understand the command

   The curl command uses -s for silent mode and sets the header to accept JSON. It fetches data from the API URL.

2. Step 2: Analyze the output

   The response variable stores the full API response body, which is expected to be JSON. The echo prints this JSON string.

3. Final Answer:

   The raw JSON response from the API -> Option B

4. Quick Check:

   Silent curl with JSON header returns JSON [OK]

Hint: Silent curl (-s) returns response body only [OK]

Common Mistakes:

• Expecting HTTP status code instead of body
• Thinking -H sets request method
• Assuming syntax error due to quotes

4. Identify the error in this script that sends JSON data to an API:

curl -X POST https://api.example.com/update -d '{"name":"John"}' -H 'Content-Type: application/json'

medium

A. The JSON data is not properly escaped

B. The -X POST option is missing

C. The Content-Type header should be text/plain

D. The URL is missing the protocol

Solution

1. Step 1: Check JSON data quoting

   The JSON string uses double quotes inside single quotes, but the inner double quotes are escaped with backslashes, which is unnecessary and can cause errors in bash.

2. Step 2: Correct quoting for JSON in bash

   Use single quotes around JSON without escaping double quotes, or use double quotes outside and escape inner quotes properly.

3. Final Answer:

   The JSON data is not properly escaped -> Option A

4. Quick Check:

   Proper JSON quoting avoids escape errors [OK]

Hint: Use single quotes around JSON to avoid escaping double quotes [OK]

Common Mistakes:

• Over-escaping quotes inside JSON
• Wrong Content-Type header
• Omitting -X POST when sending data

5. You want to write a bash script that sends a POST request with JSON data and saves the HTTP status code to a variable. Which command correctly does this?

hard

A. status=$(curl -X POST https://api.example.com/api -d '{"key":"value"}' -H 'Content-Type: application/json')

B. status=$(curl -X POST -H 'Content-Type: application/json' https://api.example.com/api -d '{"key":"value"}')

C. status=$(curl -X POST -d '{"key":"value"}' -H 'Content-Type: application/json' https://api.example.com/api -w "%{http_code}" -o /dev/null -s)

D. status=$(curl -X POST -d '{"key":"value"}' https://api.example.com/api -H 'Content-Type: application/json' -i)

Solution

1. Step 1: Understand how to capture HTTP status code

   The -w "%{http_code}" option tells curl to output the HTTP status code after the response. The -o /dev/null discards the response body, and -s silences progress.

2. Step 2: Check command correctness

   status=$(curl -X POST -d '{"key":"value"}' -H 'Content-Type: application/json' https://api.example.com/api -w "%{http_code}" -o /dev/null -s) correctly uses all these options and assigns the status code to the variable. Other options either capture the response body or include headers, not just the status code.

3. Final Answer:

   status=$(curl -X POST -d '{"key":"value"}' -H 'Content-Type: application/json' https://api.example.com/api -w "%{http_code}" -o /dev/null -s) -> Option C

4. Quick Check:

   Use -w with -o /dev/null to get status code [OK]

Hint: Use curl -w with -o /dev/null to get only status code [OK]

Common Mistakes:

• Capturing full response instead of status code
• Missing -w option for status code
• Not silencing output with -s