Pipe Operator in Bash: Unlocking the Power of Command Chaining


Bash, the default shell for most Unix-like operating systems, offers a powerful feature called the pipe operator (|). This operator allows you to connect the output of one command as the input of another, enabling seamless data flow between processes. Understanding how to use the pipe operator is essential for any Linux user or aspiring sysadmin, as it unlocks the ability to compose complex commands and build efficient workflows.

In this article, we will delve into the world of pipes in Bash. We’ll discuss their core concepts, explore practical examples, and provide tips for safe and efficient usage. By the end of this guide, you’ll have a solid understanding of how to leverage the pipe operator to take your command-line skills to the next level.

Key Takeaways

  • The pipe operator (|) in Bash connects the output of one command to the input of another, allowing for seamless data flow between processes.
  • Pipes are consistent and flexible, allowing you to chain together as many commands as needed.
  • Understanding the default file descriptors in Linux and Unix and how Bash utilizes various operators (>, <, etc.) is crucial for effective pipe usage.
  • Proper readability, maintainability, and robustness should be kept in mind when working with pipes in Bash.

What Is the Pipe Operator in Bash?

The pipe operator (|) in Bash serves as a conduit for data between processes. It connects the standard output (STDOUT) of one command to the standard input (STDIN) of another command. By piping the output of one command to the input of another, you can build powerful chains of commands that perform complex operations.

The pipe operator is extremely flexible and consistent throughout Bash scripts. When multiple pipe operators are used consecutively (e.g., command1 | command2 | command3), each pipe connects the STDOUT and STDIN of adjacent commands. This enables you to create complex workflows by seamlessly passing the output of one command as the input to another.

How to Use Pipes in Bash

Now that we understand the basics of pipes, let’s dive into practical examples to demonstrate how to use them effectively in Bash. We’ll start by exploring how to pipe output to a script and then move on to piping output to functions.

1. How to Pipe Output to a Script

Piping output to a script involves redirecting the output of a command to a file and then passing that file as input to the script. Here’s a step-by-step guide on how to achieve this:

  1. Execute the command that produces the desired output. For example, let’s assume we want to count the number of files in a directory:
    $ ls | wc -l > file_count.txt
  2. In the command above, we used the pipe operator (|) to redirect the output of the ls command to the wc -l command. The wc -l command counts the number of lines in its input. We then redirect the output of wc -l to a file named file_count.txt.

With the output redirected to a file, you can now use that file as input to a script by reading its contents within the script.

2. How to Pipe Output to a Function

Piping output to a function allows you to leverage the power of functions within your Bash scripts. Here’s an example of how to pipe output to a function:

function process_input()
  while read line; do
    # Process each line of input here
    echo "Processing: $line"

# Pipe output to the process_input function
ls | process_input

In the example above, we define a Bash function named process_input() that reads input from STDIN and processes each line. By piping the output of the ls command to the process_input function, each line of the ls output will be processed within the function.

3. How to Pipe Safely

While pipes are incredibly powerful, it’s important to implement them safely to ensure readability, maintainability, and robustness. Let’s take a look at some techniques for safe piping in Bash.

3.1 Readability with /dev/stdin

Using the /dev/stdin device file can enhance the readability of pipes. Instead of using explicit file redirection (command < file), you can pass the input directly as command-line arguments. Here’s an example:

echo "Hello, World!" | grep "Hello" /dev/stdin

In the example above, we pass the string “Hello, World!” to the grep command. Instead of redirecting the output of echo via a pipe, we use /dev/stdin as the input file for grep.

3.2 Maintainability with read

The read command in Bash allows you to safely process input line by line within a loop. By using read, you can avoid potential issues with special characters or unexpected input. Here’s an example:

while read line; do
  # Process each line of input here
  echo "Processing: $line"
done < input.txt

In the example above, we read input from the file input.txt, line by line, using the read command. This approach ensures that each line is processed correctly, regardless of its contents.

3.3 Robustness with test

The test command, also known as the [ command, helps enhance the robustness of your scripts when input is involved. By using test, you can ensure the existence or validity of input before processing it further. Here’s an example:

read -r file

# Check if the file exists
if [ -f "$file" ]; then
  # Process the file here
  echo "Processing $file"
  echo "File not found: $file"

In the example above, we read the name of a file from the user using read. We then use the [ command to check if the file exists (-f). By performing this check, we prevent potential errors or undesired behavior when processing the file.

Who Is the Pipe Operator for?

The pipe operator in Bash is an invaluable tool for a range of users, including:

  • Developers: Pipes allow developers to streamline their workflows, automate tasks, and build powerful scripts.
  • System Administrators: Pipes enable sysadmins to efficiently configure systems, process logs, and analyze data.
  • Data Engineers: Pipes play a crucial role in data processing pipelines, enabling the integration and transformation of data at scale.

Regardless of your technical background, understanding how to leverage the power of the pipe operator will undoubtedly enhance your command-line skills and productivity.


The pipe operator (|) in Bash opens up a world of possibilities when it comes to command-line usage. Whether you’re a developer, sysadmin, or data engineer, understanding how to utilize pipes effectively will unlock new levels of productivity and efficiency.

In this article, we covered the fundamental concepts of pipes in Bash and explored practical examples of piping output to scripts and functions. We also touched on techniques for safe piping, emphasizing readability, maintainability, and robustness.

Now it’s time to put your newfound knowledge into practice! Experiment with pipes, explore additional commands and utilities, and build powerful command-line workflows tailored to your needs. The possibilities are limitless.

Happy piping!

[COMPLETED]# A Beginner’s Guide to Using the Pipe Operator in Bash

If you’ve ever worked with the Linux command line or shell scripting, you’ve likely come across the pipe operator (|). But what is it exactly, and how can you use it effectively in your Bash scripts? In this article, we’ll explore the concept of pipes in Bash, understand their role in connecting processes, and learn how to leverage the pipe operator efficiently. Whether you’re a beginner or an intermediate user, this guide will help you level up your command line skills.

Key Takeaways

  • The pipe operator (|) connects the standard output (STDOUT) of one process to the standard input (STDIN) of another process.
  • Pipes are consistent everywhere in a Bash script and the pipe character (|) represents the connection between processes.
  • Multiple pipes in a command line are no different than using a single pipe. Each pipe links the STDOUT and STDIN of adjacent processes.
  • The return code of a command line with pipes is set to the last command’s return code.

What are Pipes and Why Should You Use Them?

Simply put, pipes allow you to use the output of one program as the input to another program. This means you can chain multiple commands together, passing data from one command to the next. Pipes are incredibly powerful and enable collaboration between programs.

For example, let’s say you want to list all the files in a folder and filter out the ones with the .txt extension. Instead of running separate commands, you can achieve this in a single line using pipes:

ls | grep '.txt'

In this command, the ls command lists all the files in the current directory and the grep command filters the output, displaying only the files that contain .txt in their name. By connecting these two commands with a pipe, you can seamlessly pass the output from ls to grep, creating a powerful and efficient workflow.

How to Use the Pipe Operator in Bash

Using the pipe operator in Bash is straightforward. You can connect any two commands by using the pipe character (|) between them. The STDOUT of the first command becomes the STDIN of the second command.

Let’s explore a few examples to solidify the concept:

Example 1: Simple Pipe with sed

In this example, we’ll use a basic pipe to convert lowercase text to uppercase using the sed command:

echo "hello world" | sed 's/.*/\U&/'

The echo command prints “hello world”, which then gets piped to sed. The sed command uses the substitution command (s) to transform the input to uppercase (\U) and prints the output as “HELLO WORLD”.

Example 2: An Alternative to ls -l *.txt

To illustrate the power of pipes, let’s consider a scenario where we want to list all .txt files in a directory while displaying detailed file information. Instead of using the ls -l *.txt command, let’s explore a pipe alternative:

find . -iname '*.txt' -exec ls -l {} \; | awk '{print $9, $5, $6, $7, $8}'

In this pipeline, we use the find command to locate all .txt files in the current directory (.). We then execute the ls -l command on each file found using the -exec option. The output of ls -l is piped to the awk command, which selects and prints specific columns (filename, size, month, day, and time) for a cleaner and more readable output.

How to Pipe Output to a Function

While piping output to commands is common, you can also pipe output to a function within a Bash script. This technique allows you to encapsulate functionality and reuse it across your script.

To pipe output to a function, you can define the function in your script and then use the pipe operator to pass the output to the function. Here’s an example:

function process_output() {
    while IFS= read -r line; do
        # Process each line of the output here
        echo "Processing line: $line"

ls | process_output

In this example, we define a function called process_output that accepts the output from the ls command through a pipe. The function reads each line of the input (IFS= read -r line) and processes it as needed. Here, we simply echo each line with a prefix of “Processing line:”. You can customize the function to meet your specific requirements and perform any desired actions on the input.

How to Pipe Output Safely

When working with pipes in Bash, it’s important to ensure readability, maintainability, and robustness in your scripts. Here are three techniques to help you achieve these goals when piping output:

1. Readability with /dev/stdin

Sometimes, command line arguments can interfere with piping output to commands that don’t accept command line arguments effectively. In such cases, you can use the /dev/stdin file to read input from the pipe. Here’s an example:

grep 'pattern' /dev/stdin <<< $(command)

In this example, we use the grep command to search for a specific pattern within the output of command. By redirecting the output of command to /dev/stdin using the here-string (<<<), we avoid any interference from command line arguments and ensure that grep operates solely on the piped output.

2. Maintainability with read

The read command allows you to read input from a pipe and store it in variables, making it easier to manipulate and process the data. Here’s an example:

command | while IFS= read -r line; do
    # Process each line using the $line variable
    echo "Processing line: $line"

In this example, we use a while loop to iterate over each line of the input from the command using the read command. The read command reads each line into the $line variable, which we can then use within the loop to perform custom processing.

3. Robustness with test

To ensure robustness when piping output, you can use the test command to validate the input before processing it further. By checking conditions, you can prevent errors and unexpected behavior in your scripts. Here’s an example:

if command | test -t 0; then
    # Process the piped output here
    echo "No input received from pipe."

In this example, we use the test -t 0 command to validate whether input has been received from the pipe. If input is present (test returns true), we can proceed with processing. Otherwise, we display an error message indicating that no input was received.


Pipes play a crucial role in Bash scripting, enabling seamless collaboration between commands and allowing for the efficient processing of data. By understanding the pipe operator (|) and its usage, you can streamline your workflows, reduce the need for intermediate files, and create powerful command line solutions.

In this beginner’s guide, we’ve covered the basics of pipes, explored examples of pipe usage, and discussed techniques for piping to functions safely. Remember to prioritize readability, maintainability, and robustness when working with pipes to ensure the longevity and effectiveness of your scripts.

So go ahead, start experimenting with pipes in your Bash scripts, and unlock the true potential of the command line!