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Is there a Windows command-line diff tool that is free?

I need to compare two binary files and see if they are different or not. I'm not interested in how they are different I just need to know if they are.

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up vote 9 down vote accepted

Use the comp command under cmd.exe

[C:\]comp /?
Compares the contents of two files or sets of files.                                                                    

COMP [data1] [data2] [/D] [/A] [/L] [/N=number] [/C] [/OFF[LINE]]                                                       

  data1      Specifies location and name(s) of first file(s) to compare.                                                
  data2      Specifies location and name(s) of second files to compare.                                                 
  /D         Displays differences in decimal format.                                                                    
  /A         Displays differences in ASCII characters.                                                                  
  /L         Displays line numbers for differences.                                                                     
  /N=number  Compares only the first specified number of lines in each file.                                            
  /C         Disregards case of ASCII letters when comparing files.                                                     
  /OFF[LINE] Do not skip files with offline attribute set.                                                              

To compare sets of files, use wildcards in data1 and data2 parameters.
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The added benefit of using comp is that you know it'll work on any Windows machine without having to install anything. – dwj Sep 22 '09 at 13:44
And there's also the fc command for a more flexible file comparison, in case there is a need for diff-like behavior. – A Dwarf Sep 22 '09 at 13:53
I think you should edit your answer to mention fc. That seems useful, too. – Ehtesh Choudhury Sep 12 '12 at 16:09

To simply see if they are different, you could MD5 them. For more detailed information on differences there is GNU DiffUtils for Windows.

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The title is misleading, since the author doesn't really want a full diff. He only wants to know IF 2 files are different. The distinction is important if the files are big.

Checksumming methods will obviously read both files entirely. As far as I could tell, Windows' FC and COMP both also read the entire files, even if there was a difference in the first bytes.

As John T suggests, get GNU diffutils, which includes cmp.exe. With big files, cmp will be a lot faster than COMP or FC.

That is if you need it to be a command-line tool. If you can use a GUI shareware, Total Commander has a "Compare Files" command, and a "Synchronize dirs" command which can be set to compare files by content. Both are extremely fast.

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Mr. A Dwarf has given the exact answer above. Using command prompt you can even compare two folders. To understand all with example you can check the tutorial

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