This is not a typical question. I have a fully working script but I'm interested in optimizing it.
I frequently back up photos and movies from my digital camera and cell phone to both my home/work desktops, laptops, wife's netbook, and my home NAS and often end up with multiple versions of the same files in folders of varying completeness. I previously wrote a very slow script that checked if files with the same length were identical. It was also limited to a single directory. I recently wrote this much faster script that digs recursively through a directory tree (with find instead of ls), creates a field containing size, checksum, basename and full path name, sorts them, and deletes all but the first when size and checksum are identical. The script uses pipes to avoid arrays and executes quite fast. The alphabetically first basename gets kept. I use a comma to separate the size and checksum part (to test if identical) and a backslash before the path name so I can pass everything on the pipe and separate after. There is a dash between size and checksum that was useful for debugging and I don't think impacts speed. The path ends up being part of the sort, but that is harmless since it is after the basename. The parameter substitutions are robust for either comma or backslash occurring in the file name or path (God forbid!).
Code:
#! /bin/bash
#Delete duplicate files starting at $1 recursive
dir=${1:-.} #defaults to current directory '.'
find "$dir" | { while read path; do
name=${path##*/} #basename
if [ -f "$path" ]; then #if regular file
sum=$(md5sum "$path")
echo `stat -c %s "$path"`'-'${sum%%' '*}','"$name"'\\'"$path" #length-md5sum,basename\path
else continue #skip if not regular file
fi
done } | sort | { #sort files
test=''
while read line; do
front=${line%%,*} #size-md5sum
back=${line##*\\} #full file name with path
if [ "$front" = "$test" ]; then #same size-md5sum as previous file?
echo 'deleting duplicate file '"$back"; rm "$back" #if so, delete it.
fi
test="$front"
done }
Since it works so well, I'd like to use it as a general tool. Is md5sum good enough? Does adding size (was a legacy optimization from my first script) really add any benefit in collision resistance or execution speed in the sort command? Any ideas on how to make this script faster or more robust?
Edit: sha1sum is about 13% slower than md5sum but probably eliminates collision concerns.
Mike
Last edited by Michael Stora; 08-30-2010 at 05:44 PM..
First, if your system has no md5sum and stat commands, or not at default path, the command will have the risk to delete all files under the current folder.
Second, stat command is useless in your script. if MD5 key is same, the file size should be same.
The first find and while loop can be replaced by:
Code:
find . -type f -exec md5sum {} \; > /tmp/file_list
First, if your system has no md5sum and stat commands, or not at default path, the command will have the risk to delete all files under the current folder.
Wow! Thanks for pointing this out. I'll do something to detect this and abort the script.
Quote:
Second, stat command is useless in your script. if MD5 key is same, the file size should be same.
Not true in the case of all MD5 or Sha collisions but probably no practical risk.
Quote:
The first find and while loop can be replaced by:
Code:
find . -type f -exec md5sum {} \; > /tmp/file_list
Yes but I want to keep the first file in alphabetical basename order not alphabetical directory name order. That will require more than just the checksum command.
exec can only call a single command or script (which really slows things down with disk access) but it cannot call a function (because it looks to bulletins and $PATH to find the command)--it might work if I export the function, however. It is also subject to race conditions, while piping the completed output of find is not. However, the -type flag helps remove the if then else statement:
Code:
find "$dir" -type f | { while read -r path; do
name=${path##*/} #basename
sum=$(sha1sum "$path")
echo "${sum%%' '*}"','"$name"\\"$path" #sha1sum,basename\path.
done }
Quote:
Second while loop can be replaced by: (no need to sort it)
Hello,
First of all I want to apologize because i'm not a admin or coder and maybe all my efforts to write only this small script in my life would need one week full time reading man pages and forums but...
I don't have the money to offer me to get this time and the script I want to do seems... (5 Replies)
Hello.
I'm writing a script where every file you create will generate a md5sum and store it into a text file.
Say I create 2 files, it'll look like this in the text file:
d41d8cd98f00b204e9800998ecf8427e /helloworld/saystheman
d41d8cd98f00b204e9800998ecf8427e /helloworld/test
I... (3 Replies)
Hi there,
I found something very weird!
Should I report that as a bug or is it me misusing the command?
I've got a file with a backslash in its name.
I know it's a horrible policy but it's not me.
The file came from a mac computer because this is a backup server.
Anyway, when using... (8 Replies)
I am trying to download a file and make the filename of the file be the md5sum of the URL. I know to use wgets to download the file but I do not know how to do the rest...any help would be appreciated. (2 Replies)
hi All:
i write a adduser script in perl , but I don't know how to deal with the password , for it stored as md5. and i don't use the shell
command passwd. give me some advice...thanks (1 Reply)
Hi,
I currently have a shell script that takes an RPM and scp's it to a set of remote servers and installs it.
What I would like to be able to do is make the script get the md5sum of the RPM locally (so get the md5sum of the rpm from where im running the script) and then scp the rpm to the... (0 Replies)
Is it possible to call the unix command md5sum from within a C program. I am trying to write a C program that scans a directory and computes the MD5Sum of all the files in the directory. Whenever I use md5sum 'filename' I get the error 'md5sum undeclared'. Is there a header file or some library... (3 Replies)
Hi,
I am using isql and putting the output in a file in a shell script in Linux.
However in my output i am getting the banner and a SQL prompt(at the start and the end of query output)
+---------------------------------------+
| Connected! |
| ... (6 Replies)
i downloaded a Linux distribution from a FTP site today, and i found there is a file named MD5SUM in the same directory, with the following contents:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
c9a4d963a49e384e10dec9c2bd49ad73 valhalla-SRPMS-disc1.iso
41b03d068e84d2a17147aa27e704f79b ... (1 Reply)
Hi all,
I am kinda puzzled. When and Why do we use md5sum? I've read man pages for mp5sum, but didn't get anything out of it. Please, can someone explain this to me in couple of words.
Thank you all. (1 Reply)
08-31-2010
