API interaction scripts in Bash Scripting - Mini Project: Build & Apply

API Interaction Scripts

📖 Scenario: You work in a small company that needs to get weather information from an online service. You will write a simple Bash script to interact with a public weather API to get the current temperature for a city.

🎯 Goal: Build a Bash script that fetches weather data from an API and shows the temperature for a specific city.

📋 What You'll Learn

Create a variable with the city name

Create a variable with the API endpoint URL

Use curl to get the weather data

Extract the temperature value from the JSON response using jq

Print the temperature with a friendly message

💡 Why This Matters

🌍 Real World

Many jobs require fetching data from online services using scripts. This project shows how to automate getting live data like weather.

💼 Career

Scripting API calls is a common task for system administrators, developers, and data analysts to automate data retrieval and processing.

1

Set the city variable

Create a Bash variable called CITY and set it to the exact value London.

Bash Scripting

# Create a variable called CITY and set it to London
# Your code here

Hint

Use the syntax VARIABLE_NAME="value" to create a variable in Bash.

2

Set the API URL variable

Create a Bash variable called API_URL and set it to the exact value https://api.open-meteo.com/v1/forecast?latitude=51.5074&longitude=-0.1278¤t_weather=true.

Bash Scripting

CITY="London"
# Create a variable called API_URL with the given URL
# Your code here

Hint

Use double quotes to include the full URL string in the variable.

3

Fetch weather data and extract temperature

Use curl with the variable API_URL to get the weather data. Then use jq to extract the current temperature from the JSON path .current_weather.temperature. Save this temperature in a variable called TEMP.

Bash Scripting

CITY="London"
API_URL="https://api.open-meteo.com/v1/forecast?latitude=51.5074&longitude=-0.1278&current_weather=true"
# Use curl and jq to get temperature and save it in TEMP
# Your code here

Hint

Use $(command) to capture command output into a variable.

Use curl -s to get data silently.

Use jq '.current_weather.temperature' to extract temperature.

4

Print the temperature with a message

Write a echo command to print: "The current temperature in London is X°C", where X is the value stored in the variable TEMP.

Bash Scripting

CITY="London"
API_URL="https://api.open-meteo.com/v1/forecast?latitude=51.5074&longitude=-0.1278&current_weather=true"
TEMP=$(curl -s "$API_URL" | jq '.current_weather.temperature')
# Print the temperature with a friendly message
# Your code here

Hint

Use echo and include the variable ${TEMP} inside the string.

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