cURL is a command-line tool for transferring data across various protocols, including FTP and SFTP. FTP is used to transfer files between a client and a server but operates without encryption, making it suitable for environments where data security is not a concern. In contrast, SFTP uses SSH to encrypt both file transfers and credentials, providing a more secure solution for sensitive data.

cURL allows direct interaction with FTP and SFTP servers, enabling uploads, downloads, and file listings. It simplifies the transfer process by providing authentication through the command line, which is ideal for automating tasks in scripts or cron jobs. Its ability to handle both protocols makes it a useful tool for system administrators who need to manage remote files securely or otherwise.

SFTP is the preferred protocol when encryption is needed because it protects data and credentials during transfers. FTP can still be used in less secure environments, where encryption is not required. cURL's ability to work with both protocols gives users the flexibility to choose the right solution based on their security requirements.

Steps to use cURL with FTP and SFTP:

  1. Uploading a file via FTP.
    $ curl -T example.txt ftp://ftp.example.com/public_html/ --user user:password
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
    100  1192    0     0  100  1192      0      0     --:--:-- --:--:--  --:--:--   1192

    This command uploads example.txt to the directory public_html on the FTP server ftp.example.com.

  2. Downloading a file via FTP.
    $ curl -O ftp://ftp.example.com/public_html/example.txt --user user:password
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
    100  1192    0  1192    0     0    1932      0 --:--:-- --:--:-- --:--:--   1932

    This command downloads the file example.txt from the directory public_html on the FTP server.

  3. Listing files on an FTP server.
    $ curl ftp://ftp.example.com/public_html/ --user user:password
    -rw-r--r-- 1 user group    1192 Sep 13 12:34 example.txt
    -rw-r--r-- 1 user group    2048 Sep 13 12:35 index.html

    This command lists the files in the public_html directory on the FTP server.

  4. Uploading a file via SFTP.
    $ curl -T example.txt sftp://sftp.example.com/home/user/ --user user:password
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
    100  1192    0     0  100  1192      0      0     --:--:-- --:--:--  --:--:--   1192

    This command uploads example.txt to the directory /home/user on the SFTP server sftp.example.com.

  5. Downloading a file via SFTP.
    $ curl -O sftp://sftp.example.com/home/user/example.txt --user user:password
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
    100  1192    0  1192    0     0    1932      0 --:--:-- --:--:-- --:--:--   1932

    This command downloads example.txt from the directory /home/user on the SFTP server.

  6. Listing files on an SFTP server.
    $ curl sftp://sftp.example.com/home/user/ --user user:password
    -rw-r--r-- 1 user group    1192 Sep 13 12:34 example.txt
    -rw-r--r-- 1 user group    2048 Sep 13 12:35 index.html

    This command lists the files in the /home/user directory on the SFTP server.

  7. Resuming a transfer.
    $ curl -C - -O ftp://ftp.example.com/public_html/example.txt --user user:password
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
    100  1192    0  1192    0     0    1932      0 --:--:-- --:--:-- --:--:--   1932

    This command resumes the download of example.txt from where it was interrupted.

  8. Using a private key for SFTP.
    $ curl -T example.txt sftp://sftp.example.com/home/user/ --key ~/.ssh/id_rsa --pubkey ~/.ssh/id_rsa.pub --user user
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
    100  1192    0     0  100  1192      0      0     --:--:-- --:--:--  --:--:--   1192

    This command uses the private key id_rsa and public key id_rsa.pub to upload example.txt securely to the /home/user directory on the SFTP server.

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