Bash – Keeping the number of files in the folder constant by deleting old files

bashfilesrmshell-script

I'm trying to create a script and run it in crontab every 5 min, so that the number of files in a folder always remain 50000. If there are more, I want the script to delete the old files. 

#!/bin/bash
LIMIT=500000
NO=0
#Get the number of files, that has `*.pcap` in its name, with last modified time 5 days     ago

NUMBER=$(find /mnt/md0/capture/DCN/ -maxdepth 1 -name "*.pcap" |wc -l)
if [[ $NUMBER -gt $LIMIT ]]  #if number greater than limit
 then
  del=$(($NUMBER-$LIMIT))
   if [ "$del" -lt "$NO" ]
    then
     del=$(($del*-1))
   fi
   echo $del
   FILES=$(
     find /mnt/md0/capture/DCN/ -maxdepth 1 -type f -name "*.pcap" -print0 |
       xargs -0 ls -lt |
       tail -$del |
       awk '{print $8}'
   )
  rm -f ${FILES[@]}
  #delete the originals

 fi

It doesn't really work, it doesn't run as the number of files are too large. Is there any other method to get this done?

Best Answer

I ran the command:

find /mnt/md0/capture/DCN/ -maxdepth 1 -type f -name "*.pcap" -print0 |
  xargs -0 ls -lt | tail -n "$del" | awk '{print $8}'

The problem that I observed was that awk '{print $8}' prints the time, not the file name. awk '{print $9}' would solve that.

Another problems is that xargs may run ls -lt several times which would give you a number of sorted lists of files one after the other, but the whole list would not be sorted.

But, there appear to be other simplifications one could make. You can get the oldest files with:

ls -dt /mnt/md0/capture/DCN/*.pcap | tail -n "$del"

This assumes, as your post seemed to, that the file names have no spaces, tabs, or newline characters in them.

So, the full command for deleting the oldest $del files could be:

ls -dt /mnt/md0/capture/DCN/*.pcap | tail -n "$del" | xargs rm

MORE: If your file names may contain spaces, tabs, backslashes, or quotes in them (but not newlines), use (assuming GNU ls 4.0 (1998) or newer):

ls -dt --quoting-style=shell-always /mnt/md0/capture/DCN/*.pcap |
  tail -n "$del" | xargs rm
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