How to Find the Intersection of Multiple Text Files in Linux Shell

Discover efficient methods to get the intersection of multiple text files in Linux shell using `awk`. This comprehensive guide breaks down the solutions step-by-step for both duplicate and non-duplicate scenarios.
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How to Find the Intersection of Multiple Text Files in Linux Shell

The Problem

Let's assume we have the following files:

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From this data, we aim to find the intersection, which in this case is the number 1, since it's the only common entry across all files.

The Traditional Approach

Traditionally, one might use a combination of cat, sort, and uniq commands to merge and filter through the files, such as:

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However, there's a more elegant and efficient way to achieve the same result using awk.

The Solutions

We will present two solutions using awk, depending on whether your text files contain duplicates or not.

1st Solution: Handling Duplicates

If you anticipate that your input files may contain duplicate entries within themselves, you can use the following awk command:

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Explanation

!arr2[FILENAME,$0]++: This prevents counting duplicates within the same file.

arr1[$0]++: This builds an associative array arr1 where the keys are the unique lines and the values are their counts.

The END block checks if a line appeared in all provided files (equal to ARGC-1, which is the count of all input files) and prints those lines.

2nd Solution: No Duplicates Assumed

If you are confident that there are no duplicates in your input files, you can simplify your awk command:

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Explanation

In this version, we omit the duplicate check. We simply count occurrences as before.

Again, the END block will print lines that appear in all files, following the same logic as the first solution.

Final Notes

Both methods leverage the power of awk to efficiently compute the intersection of multiple text files. Whether your files contain duplicates or not, these solutions will help streamline the process, avoiding the need for multiple intermediate files and commands.

Conclusion

Finding the intersection of multiple files in a Linux shell environment can be effortlessly accomplished with the right awk commands. By taking advantage of these techniques, you can simplify your workflow and obtain the results you need without unnecessary complexity.

Now, give these commands a try and see how they can enhance your file manipulation tasks in the Linux shell!