1. Overview

In this tutorial, we are going to create a bash script that counts the files in a directory, and if there are more files than a specific number, it removes the oldest ones.

2. The Environment

Let’s assume we have a directory that has several files in it:

$ ls 
$ ls -t ./files
file15.txt  file13.txt  file11.txt  file9.txt  file7.txt  file5.txt  file3.txt  file1.txt
file14.txt  file12.txt  file10.txt  file8.txt  file6.txt  file4.txt  file2.txt

The -t option sorts the reported files by modification time, so the newest file is displayed first. As we can see, file15.txt is the newest file, and file1.txt is the oldest one.

3. The Script

Now, let’s create the script. It should receive the limit on the number of files as an argument:


# Print usage if requested.
if [[ $1 == "--help" || $1 == "-h" ]]
    echo "Usage: $0 [files limit]"
    exit 0

# The script receives the limit as an argument.

number_of_files=$(ls ./files | wc -l)

if [ $number_of_files -gt $limit ]
    # There are more files than the limit
    # So we need to remove the older ones.
    cd files
    ls -t | tail --lines=+$(expr $limit + 1) | xargs -d '\n' rm

In the above code, wc -l counts the files in ./files using the newline character, \n, as a delimiter.

ls -t lists the files by modification time and puts the newest file first.

tail –lines=+$(expr $limit + 1) outputs the files that come right after the limit. Therefore, we now have all the files that we need to delete.

Finally, xargs -d ‘\n’, using the newline character as a delimiter, gives each file to rm as an argument so it will remove them.

4. Executing the Script

After saving the script, we need to make it executable before we can execute it:

$ ls
count_then_remove.sh  files
$ chmod u+x count_then_remove.sh

chmod u+x makes the script executable. Let’s run it:

$ ./count_then_remove.sh 5 
$ ls -t ./files
file15.txt  file14.txt  file13.txt  file12.txt  file11.txt

We can see that the script has deleted the old files. As a result, there are five files remaining.

5. Conclusion

In this short article, we learned how to create a script that keeps the number of files in a directory no more than a predetermined number.

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