How to Use a Unix Command to Find and Replace a String in Multiple Files with Output

Описание: Learn how to efficiently find and replace strings in multiple files under nested directories using Unix commands, and see the changes reflected in your output.
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This video is based on the question https://stackoverflow.com/q/67082811/ asked by the user 'Learner' ( https://stackoverflow.com/u/7699912/ ) and on the answer https://stackoverflow.com/a/67084362/ provided by the user 'Cole Tierney' ( https://stackoverflow.com/u/2820422/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use a Unix Command to Find and Replace a String in Multiple Files with Output

In the realm of command-line utilities, manipulating files efficiently is a fundamental skill. If you've ever found yourself needing to replace a string across multiple files, you might have come across the challenge of ensuring you know what changes are being made without manually checking each file.

In this guide, we're going to tackle a common scenario: finding and replacing a string in files named app.properties within nested directories, while also viewing the changes made. Let’s dive into the problem and then explore the solution step by step.

The Problem: Find and Replace a String

You need to search for all files named app.properties within your directory tree and replace the string “username” with “user”. You were able to execute this with a command, but you want to see the output reflecting those changes.

Initial Approach

Here’s the command you initially used:

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This command efficiently locates app.properties files and replaces the specified string. However, you wanted to also view these changes in output.

The Solution: Bash Process Substitution

To see the changes made without modifying the original files, we can leverage Bash process substitution. This allows us to execute a command and view the output without creating any temporary files.

Step-by-Step Guide

Creating a Dry Run:
By using the diff command alongside a process substitution for sed, we can see changes without writing to files directly. Below is a simple example:

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This command compares the original 'file' with a version that has 'bird' replaced by 'frog' and highlights the differences.

Bash Script for Automation:
You can automate this using a Bash script that processes each path and displays the changes:

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Usage Example:
Here’s how you can use the script to find and replace content. First, get all the relevant files:

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Custom Patterns:
If you want to apply another string substitution, you can pass a different pattern as an argument:

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Example Output

Let’s look at the potential output you might see from the script:

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This output clearly indicates where the replacements would occur without changing the original files.

Conclusion

By following the steps we’ve outlined, you can easily find and replace strings across multiple files while simultaneously checking what those changes would look like. This method not only saves time but also reduces the risk of accidental modifications.

Feel free to play around with different patterns or extend the script further based on your needs. Happy scripting!