Скачать или смотреть How to Insert a Number in Front of a Keyword in Perl

Learn how to use Perl to insert a sequence of numbers right before a specific keyword in your text files, ensuring that you maintain all original content.
---
This video is based on the question https://stackoverflow.com/q/63822993/ asked by the user 'Andrew' ( https://stackoverflow.com/u/14251814/ ) and on the answer https://stackoverflow.com/a/63823063/ provided by the user 'ikegami' ( https://stackoverflow.com/u/589924/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Perl how to introduce a text in front of a keyword(match) and keep the rest from a file

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Insert a Number in Front of a Keyword in Perl: A Simple Guide

Are you struggling to edit a text file in Perl without losing any data? If you are looking to insert a number before a specific keyword while keeping the rest of your file intact, you're in the right place! In this guide, we will walk through the solution to this common issue step by step.

The Problem

Imagine you have a text file containing various lines of data, and your objective is to prepend a sequence of numbers (for instance, 00000001, 00000002, etc.) in front of every occurrence of a specific keyword, which in this case is < DATA >. The challenge is to perform this manipulation without losing any existing data in the file.

Example Input

Here’s an example of what the content of your file might look like:

[[See Video to Reveal this Text or Code Snippet]]

Desired Output

You aim to achieve an output like this:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To tackle this problem, we can use Perl scripting. Below is a simple yet effective solution that utilizes Perl's powerful regex functionality to modify the file as needed.

Step-by-Step Instructions

Setup the Script: Create a new Perl script and make sure you have the required permissions to access and modify the file.

Read the File: Open your text file for reading. This is done using the open function in Perl.

Replace the Keyword: Use a regex substitution command to replace the empty string after < DATA > with a sequence-controlled counter.

Write Back to the File: Finally, overwrite the original file with the new contents.

Here is the complete Perl script:

[[See Video to Reveal this Text or Code Snippet]]

Using the Script

To use this script, follow these instructions:

Save the script as add_numbers.pl.

Run the script from your terminal:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of Key Components

\K in Regex: The \K assertion allows you to "keep" the text matched before it and only replace what comes after it. This is crucial for ensuring that we only insert our numbers right in front of the keyword without disrupting the existing data.

Counter Increment: The $counter+ + will automatically increment the number each time it finds another < DATA > keyword.

Alternative One-Liner Command

For those who prefer brevity, the task can also be accomplished with a one-liner in the terminal:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Editing a text file by inserting numbers before a specific keyword using Perl is straightforward once you understand the syntax and regex functionality. With the provided script and instructions above, you can effectively modify your files while safeguarding their original content.

Feel encouraged to tweak the script to suit your needs, and happy coding!