Deleting files but keeping some in bash

delete_old.sh

#!/usr/bin/env bash

# With this tool you can delete files using a mask, but keeping some files
# I've wrote this tool to house keep log files

# Usage: bash delete_old.sh <number of files to keep> "folder/mask" 
# If you use mask like * or ? in your command, add quotes to prevent enumeration

keep=$(($1))
folder=${2:-...}

if [ $keep -le 0 ] || [ "$folder" = "..." ]; then
    echo "Usage:"
    echo "  $(basename $0) <files_to_keep_as_integer> \"<folder/mask>\""
    exit 1
fi

files=($folder)
len=${#files[@]}

if [ $len -eq 0 ] || [ ! -f "${files[0]}" ]; then
    echo "No files found @ $folder"
    exit 2
else
    if [ $len -le $keep ]; then
        echo "Found $len files @ $folder - No need to delete"
        exit 1
    fi

    echo "Found $len files @ $folder - keeping $keep files"
fi

slice=${files[@]:0:$(($len - $keep))}
for file in $slice; do    
    if [[ -d $file ]]; then
        if rm -r $file; then
            echo "Removed dir: $file"
        else
            echo "Failed to remove dir: $file"
        fi
    else
        if [[ -f $file ]]; then
            if rm $file; then
                echo "Removed file: $file"
            else
                echo "Failed to remove file: $file"
            fi
        fi
    fi
done

exit 0