CURL - CMD
Overview
curl
is a command-line tool used to transfer data to or from a server using various protocols, including HTTP, HTTPS, FTP, FTPS, and more. It is widely utilized for testing, submitting forms, network diagnostics, downloading files, and interacting with APIs. curl
is valuable for developers, system administrators, and automation scripts due to its versatility and wide support across platforms.
Syntax
The basic syntax for curl
in CMD is:
curl [options] [URL...]
options
: This denotes the various flags and settings that you can apply to modify the behavior ofcurl
.URL
: This specifies the server URL thatcurl
will target.
Options/Flags
Below are several commonly used options in curl
:
-V, --version
: Displays thecurl
version information.-o, --output <file>
: Writes output to<file>
instead of stdout.-I, --head
: Fetches the headers only.-L, --location
: Follows HTTP redirects.-u, --user <user:password>
: Pass credentials for server authentication.-x, --proxy [protocol://]host[:port]
: Use the specified proxy.-H, --header <header>
: Pass custom header(s) to server.-X, --request <command>
: Specify a custom request method (e.g., GET, POST).-d, --data <data>
: Sends the specified data in a POST request.--data-urlencode <data>
: URL encodes and sends data in a POST request.
Default values are used for parameters not explicitly specified by the user, such as Content-Type
for POST data, which typically defaults to application/x-www-form-urlencoded
.
Examples
Example 1: Downloading a file
curl -o example.zip http://example.com/download.zip
Example 2: Using HTTP POST with data
curl -X POST -d "username=user&password=pass" http://example.com/login
Example 3: Sending JSON data
curl -H "Content-Type: application/json" -d "{\"user\":\"user\", \"pass\":\"pass\"}" http://example.com/api/login
Example 4: Saving response headers to a file
curl -D headers.txt http://example.com
Common Issues
Problem: Encountering SSL certificate verification failures.
Solution: Temporarily bypass SSL verification with -k
or --insecure
, although it’s a security risk. For a proper fix, ensure your system’s CA certificates are updated.
Problem: Data format issues with APIs.
Solution: Confirm that the Content-Type
is correctly set and that the data is properly structured (e.g., JSON).
Integration
curl
can be combined with scripts to monitor the health of web applications or to automate download and upload tasks. Here’s an example using a batch script:
@echo off
For /F "tokens=*" %%A in ('curl -s https://api.example.com/health') do (set response=%%A)
echo %response%
This script fetches the health status of an application and prints it.
Related Commands
- wget: Another command-line utility for downloading files.
- httpie: A more user-friendly HTTP client with colored output and simpler syntax for forms and JSON.
For additional resources, consult the official curl documentation.