curl

Since:		All Linux
		macOS(2001 Cheetah)
		Bash 1.0(1989)

curl is a tool for sending and receiving HTTP/HTTPS requests from the command line. You can use it for a wide range of tasks, including calling Web APIs, downloading files, and submitting form data.

Syntax

Send a basic GET request.

curl URL

Save the response to a file.

curl -o output_file URL

Save using the filename from the URL.

curl -O URL

Follow redirects.

curl -L URL

Send form data via a POST request.

curl -X POST -d "key=value&key2=value2" URL

Send JSON via a POST request.

curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' URL

Add a header.

curl -H "Authorization: Bearer token" URL

Options

Option	Description
-o file	Saves the response body to the specified file.
-O	Saves the file to the current directory using the filename from the URL.
-L	Follows redirects (301/302).
-s	Runs in silent mode, suppressing progress and error output.
-S	Used with -s to show errors only.
-w "%{http_code}"	Appends formatted output such as the HTTP status code.
-X method	Specifies the HTTP method (GET, POST, PUT, DELETE, etc.).
-H "header"	Adds a request header.
-d "data"	Specifies the body data for a POST request.
-F "field=value"	Sends data as multipart/form-data.
-u user:password	Specifies credentials for Basic authentication.
-I	Retrieves response headers only (HEAD request).
-v	Shows detailed request/response information (for debugging).
--max-time seconds	Sets the timeout duration.
-k	Skips SSL certificate verification (for development environments).

Sample Code

Sends a simple GET request. The response body is printed to standard output.

curl "https://wp-p.info/sandbox/api.php?series=like_a_dragon&id=1"
{
    "status": "ok",
    "series": "like_a_dragon",
    "title": "Like a Dragon",
    "character": {
        "id": 1,
        "name": "Kiryu Kazuma",
        "age": 37,
        "team": "Dojima Family",
        "email": "kiryu_kazuma@wp-p.info",
        "bgm": "Baka Mitai"
    }
}

Checks only the HTTP status code. The -s option enables silent mode, and -o /dev/null discards the response body.

curl -s -o /dev/null -w "%{http_code}" https://example.com
200

Inspects the response headers (uses -I to send a HEAD request).

curl -I https://example.com
HTTP/2 200
content-type: text/html; charset=UTF-8
content-length: 12345
last-modified: Thu, 01 Jan 2026 00:00:00 GMT

Sends JSON data via POST with Bearer token authentication.

sample_post_json.sh

curl -s -X POST \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer my_token_here" \
  -d '{"name":"Kiryu Kazuma","age":37}' \
  https://wp-p.info/sandbox/api.php

Run the following command:

bash sample_post_json.sh
{
    "status": "ok",
    "message": "Data received successfully.",
    "method": "POST",
    "received": {
        "name": "Kiryu Kazuma",
        "age": 37
    }
}

Downloads a file. -L follows redirects, and -sS shows errors only.

curl -sSL -o /tmp/file.tar.gz https://example.com/release.tar.gz

Uploads a file (multipart/form-data).

curl -F "file=@report.pdf" -F "title=Report" https://example.com/upload

Accesses a resource using Basic authentication.

curl -u admin:password https://example.com/admin/api

Stores the response in a variable for further processing.

sample_fetch_user.sh

response=$(curl -s "https://wp-p.info/sandbox/api.php?series=like_a_dragon&id=1")
echo "$response" | grep "name"

Run the following command:

bash sample_fetch_user.sh
        "name": "Kiryu Kazuma",

Common Mistakes

Common Mistake 1: Without -o, the response is printed to the terminal instead of being saved

By default, curl writes the response body to standard output. Without -o, the file is not saved.

curl https://example.com/file.tar.gz
（binary data floods the terminal）

Use -o to specify the output filename, or -O to use the remote filename.

curl -o file.tar.gz https://example.com/file.tar.gz

Common Mistake 2: curl stops without following redirects

By default, curl does not follow HTTP redirects (301/302). You receive only the redirect response.

curl https://example.com
<!DOCTYPE html><html><head><meta http-equiv="refresh" ...

Add -L to follow redirects automatically.

curl -L https://example.com

Notes

When using curl in scripts, combining -s (silent) and -S (show errors) as -sS is a common pattern. It is also common to use -w "%{http_code}" to check the status code and handle any response other than 200 as an error.

Only use -k (skip SSL verification) in development environments — never in production. For downloading files, wget is also a handy option.

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