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Discover how to utilize `make` and `cp` for copying only changed files in Linux. Learn step-by-step methods designed for efficiency.
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This video is based on the question https://stackoverflow.com/q/66560888/ asked by the user 'Carlos Granados' ( https://stackoverflow.com/u/1557651/ ) and on the answer https://stackoverflow.com/a/66564636/ provided by the user 'Jens' ( https://stackoverflow.com/u/648658/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Efficient File Management: Use make to Copy Only Changed Files

When managing a library in a development environment, particularly when working with header files, ensuring only the modified files are copied to a system folder becomes crucial. This approach helps save time and reduces unnecessary copying which can lead to performance degradation. If you’re a Linux user facing this dilemma — great news! With just make and cp, you can achieve this seamlessly without the need for additional tools like rsync.

The Problem: Copying Header Files

Imagine you have a folder filled with a multitude of header files (.h). Every time you need to install your library, copying these files over can become tedious, especially if most of them haven't changed since the last time you ran the command. How can we efficiently copy only the files that have changed?

The Solution: Using make and cp

To address this need, we can leverage GNU make to automate the process of only copying files that have been updated. Below, we will walk through the steps you need to follow.

Step 1: Setting Up Your Environment

Assuming you already have a directory structure set up that looks something like this:

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Ensure your local directory contains all the header files you want to manage.

Step 2: Create the Makefile

Now, let's create a Makefile in your project directory. This file will contain the rules and commands to perform the automated copying. Here's a sample Makefile you can use:

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Step 3: Understanding the Makefile Structure

This Makefile consists of several key components:

Variables:

SRCDIR denotes your source directory containing local header files.

DSTDIR refers to the directory where files will be copied.

Header Files: The HEADERS variable is dynamically populated with all .h files found in the local source directory using the ls command.

Function Definition: The copyheader function is where the magic happens. It defines how each individual header file should be copied. The command cp $$^ $$@ is executed when a header file is determined to be changed.

Automatic Dependency Generation: The line $(foreach file,$(HEADERS),$(eval $(call copyheader,$(file)))) automatically generates a rule for each header file using the function we just defined.

Default Target: The all target at the end specifies that running make will depend on all the headers in the destination directory.

Step 4: Running the Makefile

With your Makefile ready, it’s time to execute the command:

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This command will initiate the copying process. If executed again with no changes in your source headers, make will recognize that the destination files are up to date and will do nothing — saving you time and computational resources.

Conclusion

Using make to only copy changed files is a powerful technique that can streamline your development workflow in Linux. By following the steps outlined in this post, you can efficiently manage your header files without unnecessary duplication. This approach not only enhances performance but also simplifies your daily tasks, making development a more pleasant experience!

Give it a try today and enjoy the simplicity of working with your files using make!