Linux Pipes Explained: Practical Examples for Everyday Use

Table of Contents

In Linux, the vertical bar (|), commonly called a pipe, is one of the most powerful tools available on the command line. Pipes allow the output of one command to be used directly as the input of another, making it possible to build complex workflows from simple, single-purpose tools.

This article introduces the core concept of Linux pipes and walks through practical examples commonly used in development and system operations.

🧠 Basic Concept of Linux Pipes
#

A pipe connects the standard output (stdout) of one command to the standard input (stdin) of the next. Instead of writing intermediate results to a file, data flows directly from one command to another.

A simple example:

cat file.txt | grep "keyword"

Here:

cat file.txt outputs the file contents
grep "keyword" receives that output and filters matching lines

This approach keeps commands concise, readable, and efficient.

📊 Counting Specific Log Entries
#

Log analysis is a classic use case for pipes. Suppose you want to count how many times "ERROR" appears in a log file:

cat error.log | grep "ERROR" | wc -l

Command breakdown:

cat error.log — outputs the log file
grep "ERROR" — filters lines containing ERROR
wc -l — counts matching lines

This pipeline turns a multi-step task into a single command.

📁 Finding the Top 3 File Extensions
#

To identify the most common file types in a directory:

ls -l | awk '{print $NF}' | rev | cut -d. -f1 | rev | sort | uniq -c | sort -nr | head -n 3

What each stage does:

ls -l — lists files
awk '{print $NF}' — extracts filenames
rev | cut -d. -f1 | rev — extracts file extensions
sort | uniq -c — counts occurrences
sort -nr — sorts by count (descending)
head -n 3 — shows the top three

This example highlights how pipes enable powerful data processing with standard tools.

🔌 Checking Port Usage and Killing a Process
#

To find and terminate the process using port 80:

sudo netstat -tuln | grep ':80' | awk '{print $7}' | cut -d/ -f1 | xargs sudo kill -9

Pipeline steps:

netstat -tuln — lists listening ports
grep ':80' — filters port 80
awk '{print $7}' — extracts PID information
cut -d/ -f1 — isolates the numeric PID
xargs sudo kill -9 — terminates the process

⚠️ Note: Use kill -9 with caution, as it forcefully stops processes without cleanup.

📝 Viewing and Saving Output Simultaneously
#

Sometimes you want to see command output while also saving it to a file. The tee command enables this:

ps aux | tee output.txt | wc -l

Explanation:

ps aux — lists all running processes
tee output.txt — writes output to a file and forwards it
wc -l — counts the number of processes

Think of tee as a T-junction in the pipeline.

✅ Summary
#

Linux pipes transform simple commands into flexible, expressive workflows. By chaining tools together:

Temporary files become unnecessary
Commands stay modular and readable
Complex tasks become fast and repeatable

The real power of pipes lies in composability. Each command focuses on one job, and the pipe handles data flow. Mastering this concept turns the Linux command line into a highly efficient problem-solving tool—whether you’re debugging logs, managing processes, or analyzing data.