10 Must Know And Powerful CURL Commands
cURL is an essential tool for diagnosing API, TLS, DNS, and HTTP issues. Below are ten practical patterns with the command, a concise explanation of what it reveals, and real‑world scenarios where it helps most.
1. Verbose Mode
curl -v https://api.example.com/resourceWhat it shows: request headers, response headers, redirects, and TLS handshake details. When to use: first step for API failures, authentication problems, or HTTPS misconfigurations.
2. Full Wire Level Trace
curl --trace-ascii trace.log https://api.example.com/resource
# or
curl --trace trace.log https://api.example.com/resourceWhat it shows: every byte sent and received, including raw HTTP and binary data. When to use: deep debugging for corrupted payloads, proxy issues, or TLS handshake anomalies.
3. Response Headers Only
curl -s -o /dev/null -D - https://api.example.com/resourceWhat it shows: only the response headers. When to use: check status codes, caching, redirects, rate limits, and server metadata without the body.
4. Headers and Body Inline
curl -i https://api.example.com/resourceWhat it shows: response headers followed by the body in one stream. When to use: quick API checks and verifying content type or response formatting.
5. Override DNS Resolution
curl --resolve api.example.com:443:1.2.3.4 https://api.example.com/resourceWhat it does: forces the hostname to resolve to a specific IP while preserving the Host header. When to use: test new backends, bypass DNS propagation, validate SSL on a particular node, or debug load balancer routing.
6. Follow and Inspect Redirect Chains
curl -v -L https://api.example.com/redirectWhat it shows: each redirect hop and the final response. When to use: debug OAuth flows, CDN redirects, SEO issues, or redirect loops.
7. Debug Request Payloads
curl -v -X POST https://api.example.com/resource \
-H "Content-Type: application/json" \
-d '{"name":"test","enabled":true}'What it shows: the exact request line, headers, and body sent to the server. When to use: validate JSON formatting, content type, authentication headers, and payload encoding.
8. Print Only HTTP Status Code
curl -s -o /dev/null -w '%{http_code}\n' https://api.example.com/resourceWhat it shows: only the numeric HTTP status code. When to use: health checks, CI/CD assertions, and simple monitoring scripts.
9. Save Body and Debug Output Separately
curl -s https://api.example.com/resource \
-o response.json \
--stderr debug.log \
-vWhat it does: writes the response body to a file and verbose diagnostics to a separate log. When to use: reproducible debugging, sharing logs with teammates, and analyzing intermittent failures.
10. Debug TLS SSL and Mutual TLS
curl -v https://api.example.com/resource \
--cacert /path/to/ca.pem \
--cert /path/to/client.crt \
--key /path/to/client.keyWhat it shows: TLS handshake details, certificate chain validation, and client certificate usage. When to use: diagnose expired certs, CA bundle issues, or mTLS authentication failures.
Quick Reference Table
| Task | Command |
|---|---|
| Verbose | curl -v URL |
| Wire trace | curl --trace-ascii trace.log URL |
| Headers only | curl -s -o /dev/null -D - URL |
| Headers + body | curl -i URL |
| Custom resolve | curl --resolve host:port:ip URL |
| Follow redirects | curl -v -L URL |
| Payload debug | curl -v -X POST -H "Content-Type:..." -d '...' URL |
| Status code only | curl -s -o /dev/null -w '%{http_code}\n' URL |
| Separate logs | curl -s URL -o response.json --stderr debug.log -v |
| TLS and mTLS | curl -v --cacert ca.pem --cert client.crt --key client.key URL |
Wrap Up
These patterns provide fast, actionable visibility into what happens between your client and server. Use them to isolate DNS and routing issues, validate TLS and mTLS, inspect payloads, and automate health checks. If you want a printable one‑page cheat sheet or a tailored set of examples for APIs, load balancers, or mTLS, say which area to focus on and I will prepare it.
Comments
Post a Comment