API interaction scripts in Bash Scripting - Time & Space Complexity

Time Complexity: API interaction scripts

O(n)

Understanding Time Complexity

When writing scripts that talk to APIs, it is important to know how the time to finish grows as we ask for more data or make more requests.

We want to understand how the script's work changes when the number of API calls or data size changes.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

#!/bin/bash

urls=("https://api.example.com/data1" "https://api.example.com/data2" "https://api.example.com/data3")

for url in "${urls[@]}"; do
  response=$(curl -s "$url")
  echo "$response" | jq '.items[]'
done

This script loops over a list of API URLs, fetches data from each using curl, and processes the returned JSON items.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping over the list of URLs and making an API call for each.
• How many times: Once per URL in the list.

How Execution Grows With Input

As the number of URLs increases, the script makes more API calls, so the total work grows directly with the number of URLs.

Input Size (n)	Approx. Operations
10	10 API calls and processing
100	100 API calls and processing
1000	1000 API calls and processing

Pattern observation: The work grows in a straight line as the number of URLs grows.

Final Time Complexity

Time Complexity: O(n)

This means the time to finish grows directly in proportion to the number of API requests made.

Common Mistake

[X] Wrong: "The script runs in constant time because each API call is independent."

[OK] Correct: Even though calls are independent, the total time adds up with each call, so more URLs mean more total time.

Interview Connect

Understanding how your script's time grows with input size shows you can write efficient automation and predict performance, a valuable skill in real projects.

Self-Check

"What if we changed the script to fetch data from each URL in parallel? How would the time complexity change?"

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