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Discover how to efficiently copy the last 5 updated files in HDFS with a simple bash script. Follow this step-by-step guide for a seamless process!
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How to Copy the Last 5 Updated Files in HDFS Using Bash

Working with Hadoop Distributed File System (HDFS) can sometimes pose challenges, especially when it comes to managing files. One common task you may encounter is needing to copy the last updated files in HDFS to a target folder. Fortunately, with a few bash commands, you can easily identify and move these files. In this guide, we will walk through the entire process step by step.

Problem Overview

When you need to keep your HDFS organized, copying the last five updated files into a new directory can be a useful operation. This might be driven by requirements for backups, data processing steps, or just general housekeeping. The trick is to identify those files and then execute the copy command in HDFS.

Step-by-Step Solution

Step 1: Identify the Last Updated Files

To begin, we need a bash command that will allow us to list the files in your HDFS directory and determine which ones have been updated most recently. Here’s the command you'll use:

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Explanation of the Command:

hdfs dfs -ls -R /user/myfolder: Lists all files in the specified directory recursively.

awk -F" ": Processes the output to extract the necessary date and time fields.

sort -k6,7: Sorts the list based on the sixth (date) and seventh (time) columns.

tail -5: Returns the last five entries from the sorted list, which are the five most recently updated files.

Step 2: Copy the Files to the Target Directory

Now that we have the latest five files, the next task is to copy them to a target directory. Using a combination of more commands can achieve this efficiently. Below is a complete command that includes what we've done so far and adds the copying step:

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Flow of the Command:

The first part (latest_files=) executes the previous command and stores the file paths in the variable latest_files.

The second command (hdfs dfs -cp $latest_files /user/mytargetfolder) copies the identified files to the designated target directory.

Alternative Approach Using xargs

Another efficient way to handle this task involves the use of xargs. The following command combines everything into a single line that pipes the output directly into the copy command:

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What This Command Does:

Similar inputs and processing techniques as before, but we utilize xargs to handle each file copying operation individually. This method is efficient and handles multiple files gracefully.

Step 3: Verify the Files Have Been Copied

After running the copy command, it's always a good idea to confirm that the files have indeed been transferred to the target directory. You can verify this using:

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This will list the contents of your target folder, allowing you to double-check that everything is in place.

Conclusion

Managing files in HDFS doesn't have to be a daunting task. By utilizing simple bash commands, you can effectively identify and copy the last updated files to your preferred directories. Whether you choose the straightforward approach or the more efficient xargs method, you now have the tools to keep your HDFS data organized and up to date. Happy coding!