lftp can orchestrate complex, multi-protocol file transfers, acting as a programmable client for both FTP and SFTP.
Here’s lftp in action, performing a series of operations:
lftp -c "
open sftp://user@remote.server.com -u username,password;
cd /remote/path;
mirror -R /local/path/to/upload /remote/path;
lcd /local/path/to/download;
mirror /remote/path/to/files . ;
bye
"
This script connects via SFTP, navigates to a directory, uploads a local directory (mirror -R), then downloads files from the remote server into the current local directory (mirror .), and finally disconnects.
The core problem lftp solves is the need for robust, scriptable, and automated file transfers across different protocols. Unlike basic ftp or sftp commands, lftp offers advanced features like mirroring, resuming interrupted transfers, parallel transfers, and a powerful scripting language. It abstracts away the protocol differences, allowing you to write a single script for both FTP and SFTP.
Internally, lftp maintains a connection state and a current working directory for each connection. Its mirror command is particularly sophisticated. When uploading (mirror -R), it compares the local directory structure and file modification times with the remote, transferring only new or modified files. For downloading (mirror), it does the opposite, synchronizing the remote directory to the local one. The . in mirror /remote/path/to/files . signifies the current local directory.
The exact levers you control are numerous. You can specify authentication methods (password, SSH keys), set transfer modes (ASCII vs. binary), control recursion depth, define filters for files to include or exclude, and manage connection timeouts. The -e option allows executing a single command, while -c executes a series of commands within a script. You can also create dedicated script files and execute them with lftp -f your_script.lftp.
The most surprising thing about lftp is its ability to perform complex, stateful operations across multiple remote servers within a single, continuous session, without requiring explicit cd commands for every subsequent operation if you use open multiple times and manage them with set ftp:parallel-transfer-count.
The next hurdle you’ll likely encounter is handling sensitive credentials securely, moving beyond hardcoding passwords directly in scripts.