curl (Client URL) is a command-line tool used to transfer data to or from a server using various protocols (HTTP, HTTPS, FTP, etc.). For example, just some uses include:

• “GET” a URL (the rought equivalent of just pasting the URL into your browser address bar)
• Interact with an API (Usually REST, but it doesn’t have to be)
• Download a file in a scripted/automated fashion

Yes, you can find a curl tutorial just about anywhere. These are just a few of my notes for later reference, and maybe something you (dear reader) can learn from as well.

Note: while these notes are Linux specific you can also use curl via PowerShell or the Windows command line.

1. Basic Usage & Syntax

Basic GET Request

curl https://api.example.com/data

Key Concepts

• Default method: GET
• Outputs response directly to stdout (terminal)

2. Passing a Bearer Token

This is especially useful when interacting with an API that requires this level of authentication. Simply use the -H (or --header) flag to send an Authorization header containing a Bearer token.

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" https://api.example.com/protected

Passing Multiple Headers

Of course there are other times when you need to pass more than 1 header…

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
     -H "Content-Type: application/json" \
     https://api.example.com/protected

3. Saving Output / Downloading Files

Option A: Save with Remote Filename (-O / --remote-name)

Saves the file using the original filename from the URL.

curl -O https://example.com/files/document.pdf

Option B: Save with Custom Output Path (-o / --output)

Saves the output to a specific path or filename.

curl -o /path/to/local_file.pdf https://example.com/files/document.pdf

Option C: Follow Redirects (-L / --location)

Combine -L with -o or -O if the URL redirects (HTTP 301/302).

curl -L -o download.tar.gz https://example.com/download/latest

4. Capturing Output

Capture Response in a Shell Variable

response=$(curl -s https://api.example.com/data)
echo "$response"

Capture Response Body and HTTP Status Code

# Save status code to variable and body to file
http_code=$(curl -s -o response.json -w "%{http_code}" https://api.example.com/data)

echo "HTTP Status Code: $http_code"

Capture Response Headers (-i or -I)

• Include headers with body (-i):

curl -i https://api.example.com/data

• Fetch headers only (-I or --head):

curl -I https://api.example.com/data

5. Quick Reference Flags

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