The Pipe Operator

Redirection sends output to a file. But what if you want to send one command's output directly into another command as input? That's what the pipe operator | does. It connects the stdout of one command to the stdin of the next, creating a chain.

ls | grep ".txt"          # list files, then filter for .txt
cat names.txt | sort       # read file, then sort the lines
ls -la | head -n 5         # list files in detail, show only first 5

The pipe is the vertical bar character | (usually Shift + Backslash on most keyboards). The command on the left runs first, and its output flows into the command on the right. Think of it as literally piping water from one container to the next — the output of the first command pours into the input of the second.

This is one of the most powerful ideas in the terminal: small, focused commands that each do one thing well, connected together to accomplish complex tasks. Instead of needing one monolithic command that lists files AND filters by name, you combine ls (which lists) with grep (which filters). Each command stays simple; the pipe makes them powerful together.

Your workspace has a directory full of different file types. Use ls piped to grep to filter and find only the JavaScript files.

ls project/ | grep ".js"