Скачать или смотреть Echoing a Progress Bar in Perl While Executing External Processes

Learn how to display a `progress bar`, capture STDOUT, and manage external processes in Perl using standard modules.
---
This video is based on the question https://stackoverflow.com/q/70934602/ asked by the user 'osevo' ( https://stackoverflow.com/u/18086026/ ) and on the answer https://stackoverflow.com/a/70939475/ provided by the user 'Polar Bear' ( https://stackoverflow.com/u/12313309/ ) 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: Echo progress bar for while external process executing and take STDOUT when it done

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.
---
Echoing a Progress Bar in Perl While Executing External Processes

When utilizing external processes in Perl, you may find yourself needing to execute a command while displaying a progress bar and simultaneously capturing the output of that command. This guide delves into the steps required to accomplish this task using standard Perl modules without the need for forking the process. Let’s explore how we can achieve this effectively.

Problem Overview

The main task at hand is to run an external command, such as listing files in a directory, while providing visual feedback through a progress bar. Additionally, we need to capture the output of that command once it has completed. The challenge is to do this seamlessly and efficiently, especially considering that Perl offers several ways to handle external processes.

Solution Breakdown

To create a progress bar while an external process executes and capture its STDOUT when done, we can use the alarm signal feature in Perl. Here’s a breakdown of the method step-by-step:

Step 1: Setup the Environment

Before diving into the code, ensure your Perl environment is ready. The script will work with basic Perl modules, so no additional installations are needed. You will, however, be using a sample external Bash script for demonstration.

Step 2: Define the Alarm Handler

We will set up a signal handler for $SIG{ALRM}. This handler will be triggered by an alarm set to go off every second. When the signal occurs, it will print a dot (.) indicating that the external process is still running.

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

Step 3: Execute the External Process

We will use backticks (`) to run the external command. In this example, let's assume the command is a script named sig_alarm_sleep that waits for 20 seconds before listing the files.

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

Step 4: Turn Off the Alarm

Once the external command completes, we’ll disable the alarm handler to stop the progress updates.

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

Step 5: Process and Capture Output

After execution, split and format the output as needed. For this, we analyze the captured output to organize it into a more accessible format.

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

Step 6: Define the Handler Subroutine

Finally, we need to define the handler subroutine that gets called by the alarm. This prints the progress bar indicator (i.e., the dot .).

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

Complete Sample Code

Here is the complete Perl script demonstrating the above steps:

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

Sample Bash Script for Testing

Your external command script might look like the following:

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

Conclusion

By following the outlined steps in this guide, you can echo a progress bar in Perl while an external process is executing, all without needing to fork any processes. This technique not only improves user experience through real-time feedback but also ensures that you can capture important output from external commands effectively.

Whether you're developing command-line tools or other applications that require external command interaction, mastering these concepts will enhance your Perl scripting skills.