Powerful CLI Concepts

Complex tasks in Linux are often done by chaining simple commands together using Piping and Redirection.

Piping (|)

The pipe character takes the standard output (stdout) of one command and uses it as the standard input (stdin) for the next command.

Use Case: Searching the output of a lengthy command.

bash

List all processes and filter to only show processes containing 'ssh'

ps aux | grep ssh

Redirection (> and >>)

Redirection sends the output of a command to a file, rather than displaying it on the screen.

• >: Overwrites the file.
• >>: Appends to the end of the file.

Use Case: Saving the results of a scan (critical during reconnaissance).

bash

Save a list of files to 'file_list.txt'

ls -l > file_list.txt

Append another list to the same file

ls /etc >> file_list.txt