Run a shell command when a file is added

Question

I have a folder named images on my linux box. This folder is connected to a website and the admin of the site has the ability to add pictures to this site. However, when a picture is added, I want a command to run resizing all of the pictures a directory.

In short, I want to know how I can make the server run a specific command when a new file is added to a specific location.

Answer 1

Using ghotis work

Here is what I did to get the users free space:

#!/bin/bash

tail -F -n 1 /var/log/vsftpd.log | while read line; do
  if echo "$line" | grep -q 'OK LOGIN:'; then
    pid=$(sed 's/.*\[\([^]]*\)\].*/\1/g' <<< "$line")
    #the operator '<<<' doesnt exist in dash so use bash
    if [[ $pid != *"pid"* ]]; then
      echo -e "Disk 1: Contains Games:\n" > /home/vftp/"$pid"/FreeSpace.txt; df -h /media/Disk1/ >> /home/vftp/"$pid"/FreeSpace.txt
      echo -e "\r\n\r\nIn order to read this properly you need to use a text editor that can read *nix format files" >> /home/vftp/"$pid"/FreeSpace.txt
    fi
echo "checked"
#  awk '{ sub("\r$", ""); print }' /home/vftp/"$pid"/FreeSpace.txt > /home/vftp/"$pid"/FreeSpace.txt
  fi
done