Mastering curl: Essential Commands, Options, and Real‑World Examples

Overview

curl (Client URL) is a command‑line tool and library for transferring data over URLs. It supports more than 100 protocols, including HTTP/HTTPS, FTP, SMTP, POP3, RTSP and DICT. curl is lightweight, cross‑platform (Linux, Windows, macOS) and script‑friendly, making it suitable for API testing, file transfer and network diagnostics.

Typical Use Cases

API debugging – test RESTful endpoints (GET, POST, PUT, DELETE, …).

File transfer – download or upload files via FTP, SCP, SFTP, etc.

Network diagnosis – inspect server response status and headers.

Data collection – fetch web pages (respect robots.txt).

Scripting – embed network requests in shell or Python scripts.

Installation

# Debian/Ubuntu
apt install -y curl
# CentOS/RHEL
yum install -y curl

Basic Syntax

curl [options] [url]

options

are command‑line flags; url is the target resource.

Commonly Used Options

Request Control

-X, --request <method>

– specify HTTP method (GET, POST, PUT, DELETE, …). -H, --header <header> – add custom request headers; can be repeated. -d, --data <data> – send POST data (application/x‑www‑form‑urlencoded). -b, --cookie <name=value|file> – send cookies.

Data Transfer

-o, --output <file>

– write response body to a file. -O, --remote-name – download using the remote file name. -F, --form <name=content> – submit multipart/form‑data (file upload). -T, --upload-file <file> – upload a file with PUT or POST.

Output & Debugging

-v, --verbose

– show detailed request/response information. -s, --silent – suppress progress bar (errors still shown). -S, --show-error – display errors when used with -s. -D, --dump-header <file> – save response headers to a file.

Advanced Options

--proxy <host:port>

– route traffic through an HTTP or SOCKS5 proxy. -k, --insecure – skip HTTPS certificate verification (useful for testing). --limit-rate <speed> – throttle transfer speed (e.g., 100k for 100 KB/s). --retry <num> – number of retries on transient failures. --range <byte-range> – request a specific byte range for resumable downloads.

Practical Examples

GET request with custom Host header:

curl -H "Host: fake.example.com" http://192.0.2.1

Download a page to a specific file:

curl -o filename.html https://example.com/page.html

Download using remote filename: curl -O https://example.com/file.zip POST form data:

curl -d "name=John&age=30" https://api.example.com/submit

Upload a file via FTP:

curl -T report.pdf ftp://ftp.example.com/upload/

Follow redirects automatically: curl -L http://example.com Save response headers to a file:

curl -D headers.txt https://www.example.com

References

Official documentation: https://curl.se/docs/

GitHub repository: https://github.com/curl/curl