Why Process substitution (<() and >()) in Bash Scripting? - Purpose & Use Cases

The Big Idea

Discover how to skip messy temporary files and make your scripts smarter with process substitution!

The Scenario

Imagine you want to compare the contents of two files using a command like diff. Normally, you need to create temporary files or run multiple commands to prepare the data before comparing.

The Problem

Manually creating temporary files is slow and messy. You might forget to delete them, cluttering your system. Also, juggling multiple commands increases the chance of mistakes and wastes time.

The Solution

Process substitution lets you treat the output of a command as if it were a file. This means you can directly compare or process command outputs without making temporary files, making your scripts cleaner and faster.

Before vs After

✗ Before

command1 > temp1.txt
command2 > temp2.txt
diff temp1.txt temp2.txt
rm temp1.txt temp2.txt

✓ After

diff <(command1) <(command2)

What It Enables

You can seamlessly connect commands that expect files, using live command outputs instead, simplifying complex workflows.

Real Life Example

Checking differences between two live system states, like current running processes vs saved snapshots, without creating extra files.

Key Takeaways

Process substitution replaces temporary files with live command outputs.

It makes scripts cleaner and reduces manual cleanup.

It helps connect commands that need file inputs with dynamic data.