<|im_start|>user
Please write me a BASH script that classifies (recursively) the files of an input folder (that defaults to ~/Downloads). The script should create folder for each category found (Documents, Torrents, Music, Videos, Programs). Write also the commands necessary to ensure this script runs as a cronjob every day at noon.<|im_end|>
<|im_start|>assistant
Sure, here is a basic bash script that classifies files based on their extension. This script classifies documents (.doc, .docx, .txt, .pdf), torrents (.torrent), music (.mp3, .wav), videos (.mp4, .avi, .mkv), and programs (.exe, .dmg). 

```bash
#!/bin/bash

# Input directory
dir=${1:-"~/Downloads"}

# Convert the path to absolute
dir=$(readlink -f "$dir")

# Folders to organize files
declare -A folders
folders=(
  ["Documents"]="doc docx txt pdf"
  ["Torrents"]="torrent"
  ["Music"]="mp3 wav"
  ["Videos"]="mp4 avi mkv"
  ["Programs"]="exe dmg"
)

# Create folders
for folder in "${!folders[@]}"; do
  mkdir -p "${dir}/${folder}"
done

# Organize files
shopt -s globstar nullglob

for file in "$dir"/**/*.*; do
  if [[ -f $file ]]; then
    extension="${file##*.}"
    for folder in "${!folders[@]}"; do
      for ext in ${folders[$folder]}; do
        if [[ "$ext" == "$extension" ]]; then
          mv "$file" "${dir}/${folder}/"
          break 2
        fi
      done
    done
  fi
done
```

This script can be saved as `organize_files.sh`, and make sure to give it executable permissions with the command: 

```bash
chmod +x organize_files.sh
```

To run this script daily at noon using cron, you can add a cron job by opening the crontab editor:

```bash
crontab -e
```

Then, add the following line in the crontab file, replacing `/path/to/script` with the absolute path where you saved the `organize_files.sh` script:

```bash
0 12 * * * /bin/bash /path/to/script/organize_files.sh
```

This means that the script will be run every day at 12:00. Make sure the script has executable permissions and that you've specified the correct path in the crontab file.<|im_end|>
<|im_start|>user
What does the shopt -s globstar nullglob command do?<|im_end|>
<|im_start|>assistant
The command shopt -s globstar nullglob sets two shell options in bash: globstar and nullglob.

The globstar option enables the use of ** in filename patterns to match all files and zero or more directories and subdirectories. For example, echo **/*.txt would print all the .txt files in the current directory and its subdirectories.

The nullglob option prevents filename patterns that don’t match any files from expanding to themselves, and instead expands them to an empty list. For example, without nullglob, echo *.foo would print *.foo if there are no .foo files in the current directory, but with nullglob, it would print nothing.

These options can be useful for writing scripts that need to handle files recursively or avoid errors when no files match a pattern. However, they can also change the behavior of some commands or cause unexpected results if not used carefully.

To unset these options, you can use shopt -u globstar nullglob.<|im_end|>
