curl Cheat Sheet

Quick: Practical, consultant-style reference for using curl — from basic GETs to file uploads, API interactions, cookies, scripting tips and advanced flags. Friendly tone, focused on getting you productive fast.

Table of contents

1. What is curl?
2. Quick examples — Web browsing & headers
3. Downloading files
4. GET requests
5. POST requests & forms
6. API interaction & headers
7. File uploads with --form / -F
8. Cookies and sessions
9. Scripting with curl
10. Advanced & debugging flags
11. Partial downloads & ranges
12. Helpful one-line examples
13. Etiquette & safety note

What is curl?

curl (client URL) is a command-line tool for transferring data with URL syntax. It supports many protocols (HTTP/S, FTP, SCP, SMTP, IMAP, POP3, etc.) and is ideal for quick checks, automation, scripting, API calls, and sometimes creative (or mischievous) automation.

Use it when you need protocol-level control from the terminal.

Quick examples — Web browsing & headers

Downloading files

Batch download pattern (extract links then download):

curl -L http://example.com/list/ | grep '\.mp4' | cut -d '"' -f 8 | while read i; do curl http://example.com/${i} -O; done

(Adjust grep/cut to the page structure.)

GET requests

Example: fetch a JSON API (may require headers or tokens):

curl -X GET 'https://api.example.com/items?filter=all' -H 'Accept: application/json'

POST requests & forms

Examples with MongoDB Data API (illustrative):

# Insert document
curl --request POST 'https://data.mongodb-api/.../insertOne' \
  --header 'Content-Type: application/json' \
  --header 'api-key: YOUR_KEY' \
  --data-raw '{"dataSource":"Cluster0","database":"db","collection":"c","document":{ "name":"Alice" }}'

# Find one
curl --request POST 'https://data.mongodb-api/.../findOne' \
  --header 'Content-Type: application/json' \
  --header 'api-key: YOUR_KEY' \
  --data-raw '{"filter":{"name":"Alice"}}'

API interaction & headers

Examples:

curl -H 'Authorization: Bearer $TOKEN' -H 'Accept: application/json' https://api.example.com/me
curl -u 'user:password' 'https://example.com/protected'

File uploads with --form / -F

Use -F to emulate HTML form file uploads (multipart/form-data).

Notes:

• If the file is in the current directory, you can use @filename.
• If you supply an absolute path, omit the @ and pass field=/full/path.

Examples:

curl -F "email=test@me.com" -F "submit=Submit" 'https://docs.google.com/forms/d/e/FORM_ID/formResponse' > output.html
curl -F "entry.123456789=@/Users/me/pic.jpg" 'https://example.com/upload' > response.html

Cookies and sessions

Cookie file format (simple):

key1=value1;key2=value2

Scripting with curl

curl is a natural fit for bash automation. Example script patterns:

• Reusable function wrapper for API calls (add auth header once)
• Download + checksum verification loop
• Rate-limited loops for polite scraping (sleep between requests)

Example: simple reusable function

api_get(){
  local endpoint="$1"
  curl -s -H "Authorization: Bearer $API_KEY" "https://api.example.com/${endpoint}"
}

api_get "items"

Advanced & debugging flags

Examples:

curl -v https://example.com
curl --trace trace.txt https://twitter.com/
curl -s -w '%{remote_ip} %{time_total} %{http_code}\n' -o /dev/null http://ankush.io
curl -L 'https://short.url' --connect-timeout 0.1

Partial downloads & ranges

Use -r to request byte ranges from HTTP/FTP responses (helpful for resuming or grabbing file snippets).

Helpful one-line examples

# Show headers only
curl -I https://example.com

# Save response to file quietly
curl -sL https://example.com -o page.html

# POST JSON and pretty-print reply (using jq)
curl -s -H "Content-Type: application/json" -d '{"name":"A"}' https://api.example.com/insert | jq

# Upload file with field name "file"
curl -F "file=@./image.jpg" https://api.example.com/upload

# Send cookies from file and save response headers
curl -b cookies.txt -D headers.txt https://example.com

# Send URL-encoded form field
curl -d "field1=value1&field2=value2" -X POST https://form-endpoint

Request example (SMS via textbelt — use responsibly)

curl -X POST https://textbelt.com/text \
  --data-urlencode phone='+[E.164 number]' \
  --data-urlencode message='Please delete this message.' \
  -d key=textbelt

Response example: {"success":true,...} (service-dependent)

Etiquette & safety note

• Only target servers or forms you own or have explicit permission to test. Abuse (flooding, unauthorized automation, fraud) is illegal and unethical.
• Prefer --connect-timeout and rate-limiting in scripts to avoid hammering servers.
• Keep secrets out of command history — use environment variables or --netrc where appropriate.