How to diff two folders from a Windows command prompt

In most cases where I need to compare two folders recursively on a Windows system I use my go-to tool Beyond Compare. It is an excellent utility, and one that I think should be among the first utilities any developer should install on a new machine.

However, today I was doing a reconciliation as part of a very large file migration project that required comparing two folders that each contained hundreds of millions of files spread across thousands of sub-folders. BC was having a lot of trouble and choked on many of my comparisons. It just wasn’t the tool for today’s job. I needed another solution.

Necessity mothered some invention and I found an inventive way to use a combination of command switches on  RoboCopy to perform the comparison. If you are not familiar with RoboCopy, and you do a lot of mass copying of files, you need to stop what you are doing and learn about it pronto. It is a supercharged version of XCopy that has been included with Windows since Vista. It has a ton of great features such as multi-threaded file copying, selectively copying changed files, and resumable copies that make it a must especially for big file copy jobs over flaky network connections.

Diff Command Using RoboCopy

So here’s the command to perform a basic comparison of two folders and write a log file listing the differences.

ROBOCOPY “\\FileShare\SourceFolder” “\\FileShare\ComparisonFolder” /e /l /ns /njs /njh /ndl /fp /log:reconcile.txt

Explanation of the command switches used above:

/e  Recurse through sub-directories (including empty ones)
/l  Don’t modify or copy files, log differences only
/fp  Include the full path of files in log (only necessary if you omit /ndl)
/ns  Don’t include file sizes in log
/ndl  Don’t include folders in log
/njs   Don’t include Job Summary
/njh   Don’t include Job Header
/log:reconcile.txt   Write log to reconcile.txt (Recreate if exists)
/log+: reconcile.txt   (Optional variant) Write log to reconcile.txt (Append if exists)

Usage Notes and Warnings Regarding the /NDL Option

The /NDL option is a handy way to suppress the inclusion of every folder checked (regardless of whether it contains differences) in the log, but there because of the way it works it is not a good idea in all circumstances. Consider the following before you use /NDL.

  • Folders that exist only on source or destination are not logged unless at least one mismatched file is present or a source file is missing on destination.
  • Folders that exist only on the destination are not logged at all regardless of contents.

If you omit the /NDL option, it is necessary to include the /FP option if you want full paths listed for each file.

Example Output

(with /NDL option)

*EXTRA File         c:\dest\log.txt
New File              c:\source\newfolder\Blah.txt
Newer                 c:\source\Files\CONCORD.DAT
New File              c:\source\Files\COWCO.DAT

(without NDL Option)

 c:\work\test\source\    (extraneous folder listing)
*EXTRA Dir      c:\dest\newfolderdest\
*EXTRA Dir      c:\dest\newfolderrestempty\
*EXTRA File     c:\dest\log.txt
New Dir           c:\source\newfolder\
New File          c:\source\newfolder\Blah.txt
New Dir           c:\source\newfolderempty\
c:\source\Files\   (extraneous folder listing)
Newer             c:\source\Files\CONCORD.DAT
New File          c:\source\Files\COWCO.DAT
c:\test\source\FilesSame\   (Included despite no diffs)


13 Responses

  1. I suggest to try “Long Path Tool” program. It’s really work for me.

  2. […] /how-to-diff-two-folders-from-a-windows-command-prompt/ […]

  3. […] via How to diff two folders from a Windows command prompt | Improving Software. […]

  4. Worked well for me to check my NAS migration. I was able to utilize the other switches especially the number of processor threads. Nicely done.

  5. Beyond Compare is buggy — attempted to move files on other devices. Maybe it worked in the past, but in 2016 — dangerous.

  6. Thanks !!!! This worked .

  7. Thank you so much for posting this! It is exactly what I needed. I left off off the /njs and /njh since the output “header” echoes options used, the source and dest folders and “summary” shows total dirs, files, bytes, skips, mismatches, failed and extras… very helpful for verification of what was done.

  8. […] and a great solution for some of your more challenging backup needs.  Leveraging some help from this post, I constructed the following robocopy command to see what July photos still needed backing […]

  9. Thank you so much for this. I had to compare two super-huge directories at work and I had to use only the software that was already installed on my computer.

    I have been using Robocopy everyday for incremental backups of my Documents folder to a drive on the LAN but I never thought to use Robocopy with the /l option (don’t modify or copy files, log differences only). Your solution worked perfectly for me.

    Thanks for saving me a bunch of time!

  10. Thank you – excellent suggestions. However, I run into a practical problem: when a new folder with numerous subdirectories has been added, robocopy will list, besides the new root directory that I want, also all the subdirectories of it (which is tautological, as when the root is missing, then obviously all files and all subdirectories must be, too). Any ideas on how to get only the new root dirs listed?

  11. Thanks! Drag that txt file into Excel and you can then sort/filter.

  12. […] you want to compare the 2 folders, use the technique here. It basically uses the command line and robocopy (included with […]

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