Pipes

Connecting Commands Together

The pipe operator | takes the output of one command and feeds it as input to the next. This is one of the most powerful ideas in Linux: small tools that do one thing well, combined into powerful pipelines.

Basic Syntax

command1 | command2

The standard output (stdout) of command1 becomes the standard input (stdin) of command2.

Example

cat notes.txt | grep "daily"

This does two things:

1. cat notes.txt reads the file and prints it
2. grep "daily" reads that output and filters for lines containing "daily"

If notes.txt contains:

Learn Linux
Practice daily
Have fun

Output:

Practice daily

Longer Pipelines

Pipes can be chained indefinitely:

cat notes.txt | grep "L" | head -n 1

1. cat reads the file
2. grep "L" keeps lines with "L"
3. head -n 1 keeps only the first

Output:

Learn Linux

The Philosophy

The Unix philosophy: "Write programs that do one thing and do it well. Write programs to work together." Pipes are the glue.

Instead of one giant program that filters, counts, and sorts, you have grep, wc, and sort — each tiny, each composable.

Your Task

Use a pipe to pass the contents of notes.txt through grep to find lines containing daily.