What is the Purpose of the -L Flag in Curl?

The -L or --location flag in curl enables automatic handling of HTTP redirects, making it follow redirect responses to their final destination.

How HTTP Redirects Work

When a server moves content to a new location, it responds with a redirect status code (typically 301, 302, 303, or 307) and includes the new URL in the Location header. By default, curl stops at the redirect response and doesn't follow it.

Without -L Flag (Default Behavior)

# Without -L, curl stops at the redirect
curl -I http://example.com/old-page

Response: HTTP/1.1 301 Moved Permanently Location: http://example.com/new-page Content-Length: 0

With -L Flag

# With -L, curl follows the redirect automatically
curl -L http://example.com/old-page

This will automatically make a second request to http://example.com/new-page and return the final content.

Common Use Cases

1. Basic URL Following

# Follow redirects to get the final content
curl -L https://short.ly/abc123

2. Downloading Files Through Redirects

# Download a file that might be redirected
curl -L -o file.zip https://example.com/download-link

3. API Endpoints with Redirects

# Follow API redirects while preserving headers
curl -L -H "Authorization: Bearer token" https://api.example.com/endpoint

Method-Specific Behavior

GET and HEAD Requests

The -L flag works automatically with GET and HEAD requests:

# Both will follow redirects
curl -L https://example.com
curl -L -I https://example.com  # HEAD request

POST Requests

For POST requests, curl requires additional flags to follow redirects:

# POST request following all redirect types
curl -L --post301 --post302 --post303 -X POST -d "data=value" https://example.com

Explanation of POST redirect flags: - --post301: Follow 301 redirects with POST method - --post302: Follow 302 redirects with POST method
- --post303: Follow 303 redirects (typically changes to GET)

Advanced Options

Limiting Redirect Count

# Follow maximum 5 redirects
curl -L --max-redirs 5 https://example.com

Viewing Redirect Chain

# Show all redirect steps
curl -L -v https://example.com

Preserving Original Method

# Keep POST method through all redirects
curl -L --post301 --post302 --post303 -X POST https://example.com

Security Considerations

When using -L, be aware that: - Redirects can lead to different domains - Sensitive headers might be sent to unintended servers - Infinite redirect loops are possible (use --max-redirs to prevent)

Real-World Example

# GitHub releases often redirect to CDN URLs
curl -L -o latest-release.tar.gz https://github.com/user/repo/releases/latest/download/package.tar.gz

This command will follow the GitHub redirect to the actual CDN URL and download the file directly.

The -L flag is essential for robust web scraping and API interactions where redirects are common.