Introduction to the curl Command: Syntax, Options, and Examples

curl command is a file transfer tool that works from the command line using URL syntax. It supports uploading and downloading over many protocols (HTTP, HTTPS, FTP, etc.) and offers features such as POST, cookies, authentication, partial downloads, user‑agent strings, rate limiting, progress display, and more.

Syntax : curl [options] [URL] . Common options include:

-a, --append : Append to target file when uploading.

-A, --user-agent <string> : Set the User‑Agent header.

-b, --cookie <name=string/file> : Provide cookie data or file.

--basic : Use HTTP Basic authentication.

-c, --cookie-jar <file> : Write cookies to a file after the operation.

-C, --continue-at <offset> : Resume a transfer at the given offset.

-d, --data <data> : Send data via HTTP POST.

-D, --dump-header <file> : Write response headers to a file.

-o, --output <file> : Write output to the specified file.

-O, --remote-name : Save with the remote file name.

-R, --remote-time : Preserve remote file timestamp.

-u, --user <user[:password]> : Specify server user and password.

-U, --proxy-user <user[:password]> : Specify proxy authentication.

Examples :

Download a single file: curl http://man.linuxde.net/text.iso

Download multiple files: curl -o http://man.linuxde.net/text1.iso -o http://man.linuxde.net/text.iso

Download with progress bar and output file: curl http://man.linuxde.net/text.iso -o filename.iso --progress-bar

Limit download speed: curl http://man.linuxde.net/text.iso --limit-rate 50k

Set maximum file size: curl http://man.linuxde.net/text.iso --max-filesize 1000k

Download from FTP with credentials: curl -u ftpuser:ftppass -O ftp://ftp_server/public_html/xss.php

Resume a broken download: curl http://man.linuxde.net/text.iso -C <offset> or curl -C - http://man.linuxde.net/text.iso

Upload a file: curl --form "[email protected]" http://hostname/resource

Additional HTTP request examples include viewing page source ( curl www.so.com ), performing GET and POST requests, displaying headers ( curl -i http://www.so.com ), showing the transfer process ( curl -v www.so.com ), using cookies, adding custom headers, and basic authentication ( curl -u name:password http://www.so.com ).

For more detailed usage, refer to the official curl manual at http://man.linuxde.net/curl .