HTTP requests with curl in scripts in Bash Scripting - Time & Space Complexity

Time Complexity: HTTP requests with curl in scripts

O(n)

Understanding Time Complexity

When running HTTP requests in a script, it is important to understand how the time to complete grows as you make more requests.

We want to know how the script's running time changes when the number of curl requests increases.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

for url in "$@"; do
  curl -s "$url" > /dev/null
  echo "Fetched $url"
done
    

This script takes a list of URLs and fetches each one using curl, printing a message after each fetch.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The for-loop that runs curl for each URL.
• How many times: Once for each URL passed to the script.

How Execution Grows With Input

Each additional URL adds one more curl request, so the total time grows directly with the number of URLs.

Input Size (n)	Approx. Operations
10	10 curl requests
100	100 curl requests
1000	1000 curl requests

Pattern observation: The time grows linearly as you add more URLs.

Final Time Complexity

Time Complexity: O(n)

This means the total time increases in direct proportion to the number of URLs you fetch.

Common Mistake

[X] Wrong: "Running multiple curl commands in a loop happens instantly or all at once."

[OK] Correct: Each curl command waits for the server response before moving on, so the time adds up with each request.

Interview Connect

Understanding how loops with network calls grow helps you write efficient scripts and explain your reasoning clearly in interviews.

Self-Check

"What if we ran multiple curl requests in parallel instead of one after another? How would the time complexity change?"

Practice

1. What does the curl command do in a bash script?

easy

A. It creates a new directory on the system.

B. It sends HTTP requests to websites or APIs.

C. It compiles the bash script into an executable.

D. It displays the current date and time.

Solution

1. Step 1: Understand the purpose of curl

   The curl command is designed to transfer data from or to a server using various protocols, mainly HTTP.

2. Step 2: Match curl's function to the options

   Among the options, only sending HTTP requests matches curl's purpose.

3. Final Answer:

   It sends HTTP requests to websites or APIs. -> Option B

4. Quick Check:

   curl = HTTP requests [OK]

Hint: Remember curl talks to websites using HTTP [OK]

Common Mistakes:

• Confusing curl with system commands like mkdir or date
• Thinking curl compiles scripts
• Assuming curl only downloads files

2. Which of the following is the correct syntax to send a GET request with curl in a bash script?

easy

A. curl -send https://example.com

B. curl --post https://example.com

C. curl -X GET https://example.com

D. curl get https://example.com

Solution

1. Step 1: Identify the correct curl option for GET

   The -X GET option explicitly tells curl to use the GET method, which is the default.

2. Step 2: Check other options for correctness

   Options B, C, and D use invalid or incorrect flags for curl.

3. Final Answer:

   curl -X GET https://example.com -> Option C

4. Quick Check:

   GET request syntax = curl -X GET [OK]

Hint: Use -X GET to specify GET method explicitly [OK]

Common Mistakes:

• Using --post instead of -X POST for POST requests
• Typing invalid flags like -send or get
• Omitting the URL

3. What will the following script output?

response=$(curl -s -o /dev/null -w "%{http_code}" https://httpbin.org/status/200)
echo $response

medium

A. 200

B. OK

C. 404

D. curl: command not found

Solution

1. Step 1: Understand curl options used

   The -s option silences progress, -o /dev/null discards output, and -w "%{http_code}" prints the HTTP status code.

2. Step 2: Analyze the URL and expected status

   The URL https://httpbin.org/status/200 returns HTTP status 200, so the variable response will hold "200".

3. Final Answer:

   200 -> Option A

4. Quick Check:

   HTTP status code = 200 [OK]

Hint: Use -w "%{http_code}" to get HTTP status code [OK]

Common Mistakes:

• Expecting full page content instead of status code
• Missing quotes around %{http_code}
• Not using -s to silence output

4. Identify the error in this script snippet:

curl -X POST -d 'name=John' https://example.com/api
if [ $? -eq 0 ]; then
  echo "Success"
else
  echo "Failed"
fi

medium

A. No error; script works correctly

B. Missing quotes around URL

C. Single quotes prevent variable expansion in -d

D. Using -X POST with -d is invalid

Solution

1. Step 1: Check curl command syntax

   The command uses -X POST with -d 'name=John' correctly to send POST data.

2. Step 2: Verify script logic for success check

   The script checks the exit status $? properly and echoes success or failure accordingly.

3. Final Answer:

   No error; script works correctly -> Option A

4. Quick Check:

   Script syntax and logic = correct [OK]

Hint: Check exit status $? after curl for success [OK]

Common Mistakes:

• Thinking single quotes block variable expansion here (no variables used)
• Assuming -X POST and -d can't be combined
• Forgetting to check curl exit status

5. You want to write a bash script that sends a JSON POST request with curl to https://api.example.com/data and saves the response to response.json. Which script snippet correctly does this?

hard

A. curl -X POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data >> response.json

B. curl -POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data > response.json

C. curl -X POST -H Content-Type application/json -d '{"key":"value"}' https://api.example.com/data > response.json

D. curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json

Solution

1. Step 1: Check HTTP method and headers

   curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json correctly uses -X POST and sets the header -H 'Content-Type: application/json' with quotes.

2. Step 2: Validate JSON data and output redirection

   curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json uses valid JSON with escaped quotes and redirects output with > to overwrite response.json.

3. Step 3: Identify errors in other options

   curl -POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data > response.json uses invalid -POST flag and unquoted JSON keys. curl -X POST -H Content-Type application/json -d '{"key":"value"}' https://api.example.com/data > response.json misses quotes around header value. curl -X POST -H 'Content-Type: application/json' -d '{key:value}' https://api.example.com/data >> response.json appends with >> and has invalid JSON keys.

4. Final Answer:

   curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json -> Option D

5. Quick Check:

   Correct POST JSON syntax and output redirection = curl -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/data > response.json [OK]

Hint: Use -H for headers, -d with valid JSON, > to save output [OK]

Common Mistakes:

• Forgetting quotes around JSON keys and values
• Using invalid curl flags like -POST
• Appending instead of overwriting output file