Using curl to Test APIs

Introduction

curl is a versatile command-line tool used to send HTTP requests. Developers and system administrators often use it to test APIs, download files, and debug network issues. This guide walks through common tasks with curl.

Prerequisites

• A Linux or macOS system (Ubuntu typically has curl preinstalled).
• Basic familiarity with HTTP requests.

Send a Simple GET Request

curl https://api.github.com/users/octocat

This fetches a JSON object containing details for the GitHub user octocat.

Add Headers

Include an authorization header when accessing APIs:

curl -H "Authorization: Bearer $TOKEN" https://api.example.com/data

POST Data

Send a JSON payload to an API endpoint:

curl -X POST -H "Content-Type: application/json" \
-d '{"name":"test","value":42}' \
https://api.example.com/submit

Save Output to a File

curl -o response.json https://api.github.com/users/octocat

Pretty-print JSON with jq (Optional)

Combine curl with jq for readable JSON output:

curl https://api.github.com/users/octocat | jq .

Automating with a Script

Save multiple curl calls in a shell script (test-api.sh):

#!/bin/bash
curl -s https://api.example.com/health | jq .
curl -s -H "Authorization: Bearer $TOKEN" https://api.example.com/data | jq .

Run with:

bash test-api.sh

Troubleshooting

Common Issues

SSL certificate errors

Use -k to ignore SSL warnings (not recommended in production):

curl -k https://self-signed.badssl.com/

Debugging requests Use -v for verbose output:

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