Syntax Overview

cURL follows a straightforward invocation pattern:

curl [options] <URL>

Core Options Reference

Option	Description
-A, --user-agent	Specifies client identification string
-b, --cookie	Sends cookies from string or file
-c, --cookie-jar	Persists cookies to file after transfer
-C, --continue-at	Resumes interrupted transfers
-D, --dump-header	Stores response headers to file
-e, --referer	Sets HTTP Referer header
-f, --fail	Returns error codes without server error pages
-o, --output	Writes content to specified filename
-O, --remote-name	Saves using the remote filename
-r, --range	Requests specific byte ranges
-s, --silent	Suppresses progress meters
-T, --upload-file	Transmits local files to server
-u, --user	Provides authentication credentials
-w, --write-out	Displays custom metrics after completion
-x, --proxy	Routes through specified proxy
-#, --progress-bar	Shows visual transfer progress

Basic Resource Retrieval

Fetch a web page content:

curl https://api.example.org

This operation sends a GET request and streams the response body to stdout, useful for testing connectivity or viewing raw HTML.

Managing Output

Shell Redirection

Leverage Unix output redirection to capture content:

curl https://api.example.org >> response.html

Explicit File Naming

Use lowercase -o to define the destination filename explicitly:

curl -o response.html https://api.example.org

Preserving Remote Filenames

Uppercase -O retains the original server-side filename:

curl -O https://api.example.org/assets/image.jpg

Note that -O requires the URL to include a specific filename rather than a directory path.

Response Analysis

Extract HTTP status codes for debugging:

curl -o /dev/null -s -w "%{http_code}" https://api.example.org

This suppresses download progress and body output, returning only the numeric status code (200, 301, 404, etc.).

Proxy Configuration

Route traffic through intermediary servers:

curl -x proxy.example.com:8080 https://external-site.com

Cookie Management

Persisting Session Data

Store cookies for subsequent authenticated requests:

curl -c session.dat https://api.example.org/login

Capturing Response Headers

Save server headers including Set-Cookie directives:

curl -D headers.txt https://api.example.org

Note that -D captures the entire header block, while -c extarcts only cookie data.

Reusing Stored Sessions

Attach previously saved cookies to new requests:

curl -b session.dat https://api.example.org/dashboard

Request Customization

Client Identification

Masquerade as specific browser versions:

curl -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36" \
  https://api.example.org

Referer Spoofing

Bypass hotlink protection mechanisms:

curl -e "https://trusted-domain.com" \
  https://api.example.org/protected/image.jpg

File Transfer Operations

Sequential Batch Downloads

Download numbered sequences using bracket expansion:

curl -O https://api.example.org/docs/manual_[1-5].pdf

This retrieves manual_1.pdf through manual_5.pdf sequentially.

Partial Content Retrieval

Download large files in segments for parallel processing:

curl -r 0-1048576 -o part_aa.bin https://api.example.org/large-archive.zip
curl -r 1048577-2097152 -o part_ab.bin https://api.example.org/large-archive.zip
curl -r 2097153- -o part_ac.bin https://api.example.org/large-archive.zip
cat part_*.bin > complete-archive.zip

Transfer Progress Visualization

Enable hash-mark progress indicators:

curl -# -O https://api.example.org/distribution.tar.gz

Resuming Interrupted Transfers

Continue broken downloads automatically:

curl -C - -O https://api.example.org/distribution.tar.gz

The hyphen after -C instructs cURL to determine the resume point automatically.

Uploading Files

Transmit local files to remote servers:

curl -T report.csv -u username:secretkey ftp://ftp.example.org/incoming/