curl Command in Linux: Practical Examples

Quick take: The curl command transfers data to and from servers. Download with curl -O url, follow redirects with -L, send headers with -H, and POST data with -d. It is the go-to tool for testing APIs from the terminal.

Introduction

The curl command transfers data over HTTP, HTTPS, FTP, and many other protocols. Administrators use it to download files and check endpoints; developers use it constantly to test REST APIs without leaving the terminal. Its flags map directly to the parts of an HTTP request — method, headers, body, and authentication.

This guide covers downloading files, inspecting responses, and building API requests with headers, data, and credentials.

Syntax

The basic syntax of the curl command is:

curl [OPTIONS] URL

Common Options and Parameters

The most useful options and parameters for the curl command:

Practical Examples

Real curl commands you can run today:

# Download a file with its remote name
curl -O https://example.com/app.tar.gz
# Save to a chosen filename and follow redirects
curl -L -o app.tar.gz https://example.com/latest
# Show only response headers
curl -I https://example.com
# GET a JSON API endpoint
curl https://api.example.com/v1/users
# POST JSON to an API
curl -X POST -H 'Content-Type: application/json' -d '{"name":"Irfan"}' https://api.example.com/users
# Send basic authentication
curl -u admin:secret https://api.example.com/admin

Testing REST APIs with curl

curl is the de facto tool for exercising HTTP APIs from the terminal. Its flags map directly onto the parts of a request, so you can reproduce almost any client call.

# GET with a bearer token, pretty-printed via jq
curl -s -H 'Authorization: Bearer $TOKEN' https://api.example.com/users | jq

# Create a resource with JSON
curl -X POST https://api.example.com/users \
  -H 'Content-Type: application/json' \
  -d '{"name":"Irfan","role":"admin"}'

# Update with PUT, delete with DELETE
curl -X PUT  https://api.example.com/users/7 -d '{"role":"editor"}'
curl -X DELETE https://api.example.com/users/7

Piping the response into jq turns dense JSON into readable, queryable output, making curl plus jq a complete API-testing workflow.

Debugging Requests with curl

When a request misbehaves, curl can show exactly what is happening on the wire. The -v (verbose) flag prints the request and response headers, while -w reports timing and status without the body.

# See the full request/response exchange
curl -v https://example.com

# Print just the HTTP status code
curl -s -o /dev/null -w '%{http_code}\n' https://example.com

# Measure how long the request takes
curl -s -o /dev/null -w 'time: %{time_total}s\n' https://example.com

These checks quickly distinguish a DNS or TLS problem from an application error — invaluable when a service is up but a specific endpoint is failing.

Tips and Best Practices

• Add -s for clean output in scripts, and combine with -S (-sS) so errors still show while progress is hidden.
• Use -I to check status codes and headers quickly — perfect for verifying redirects or caching.
• Pipe JSON responses into jq for readable, queryable output: curl -s url | jq.

Final Thoughts

curl is the Swiss-army knife of HTTP from the command line — downloading files, checking endpoints, and exercising APIs with full control over method, headers, body, and auth. Learn -O, -L, -I, -H, and -d, and you can test and automate almost any web request. For mirroring sites or resumable downloads, pair it with wget.