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

Answer 1

#!/bin/bash

tail -F -n0 /var/log/vsftpd.log | while read line; do
  if echo "$line" | grep -q 'OK UPLOAD:'; then
    filename=$(echo $line | cut -d, -f2 |awk '{print $1}')
    filename="${filename%\"}"
    filename="${filename#\"}"
    #sleep 1s
    if [ -s $filename ]; then
      # do something with $filename
      echo $filename
    fi
  fi
done

Answer 2

I don't know how people are uploading content to this folder, but you might want to use something lower-tech than monitoring the directory with inotify.

If the protocol is FTP and you have access to your FTP server's log, I suggest tailing that log to watch for successful uploads. This sort of event-triggered approach will be faster, more reliable, and less load than a polling approach with traditional cron, and more portable and easier to debug than something using inotify.

The way you handle this will of course depend on your FTP server. I have one running vsftpd whose logs include lines like this:

Fri May 25 07:36:02 2012 [pid 94378] [joe] OK LOGIN: Client "10.8.7.16"
Fri May 25 07:36:12 2012 [pid 94380] [joe] OK UPLOAD: Client "10.8.7.16", "/path/to/file.zip", 8395136 bytes, 845.75Kbyte/sec
Fri May 25 07:36:12 2012 [pid 94380] [joe] OK CHMOD: Client "10.8.7.16", "/path/to/file.zip 644"

The UPLOAD line only gets added when vsftpd has successfully saved the file. You could parse this in a shell script like this:

#!/bin/sh

tail -F /var/log/vsftpd.log | while read line; do
  if echo "$line" | grep -q 'OK UPLOAD:'; then
    filename=$(echo "$line" | cut -d, -f2)
    if [ -s "$filename" ]; then
      # do something with $filename
    fi
  fi
done

If you're using an HTTP upload tool, see if that tool has a text log file it uses to record incoming files. If it doesn't consider adding some sort of logger function to it, so it'll produce logs that you can tail.

Answer 3

If the file is added through an HTTP upload, and if your server is apache, you might want to check mod_security.

It enables you to run a script for every upload made through HTTP POST.

Answer 4

You might want to look at inotify

The inotify API provides a mechanism for monitoring file system events. Inotify can be used to monitor individual files, or to monitor directories. When a directory is monitored, inotify will return events for the directory itself, and for files inside the directory.

Answer 5

Like John commented the inotify API is a starting point, however you might be interested in some tools that use this API to perform file notification tasks:

For example incron which can be used to run cron-like tasks when file or directory changes are detected.

Or inotify-tools which is a set of command-line tools that you could use to build your own file notification shell script.

If you look at the bottom of the Wiki pake for inotify-tools you will see references to even more tools and support for higher-level languages like Python, Perl or Ruby (example code).

Answer 6

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