FC.exe

Compare the contents of two files or sets of files. Display any lines which do NOT match.

Syntax
      FC /B pathname1 pathname2

      FC [options] pathname1 pathname2

Key
   /B  : Perform a binary comparison.

options
   /C  : Do a case insensitive string comparison

   /A  : Displays only first and last lines for each set of differences.

   /U  : Compare files as UNICODE text files.
   /L  : Compares files as ASCII text. (default)

   /N  : Display line numbers (ASCII only)

   /LBn: Limit the number of lines that will be read, "n" sets a maximum number
         of mismatches after which the File Comparison will abort (resync failed)
         When FC aborts (resync failed) then "n" number of mismatches will be shown. 

  /nnnn  : Specify a number of consecutive lines that must match after a mismatch.
           This can be used to prevent the display of the two files from getting 
           too out of sync

  /T     : Do not expand tabs to spaces.
  /W     : Compress white space (tabs and spaces) for comparison.

To compare sets of files, use wildcards in pathname1 and pathname2 parameters.

Powershell also has an Alias FC for the Format-Custom cmdlet, therefore to run the 'old' FC under powershell you need to explicitly run C:\windows\system32\fc.exe

To identify 2 identical files use this syntax:

   FC file1.txt file2.txt | FIND "FC: no dif" > nul 
   IF ERRORLEVEL 1 goto :s_files_are_different

Example:

If two files are compared and the four lines of text match as follows

1: different
2: same
3: same
4: different

Specifying /nnnn =2 the file compare will display the 4th line and continue
Specifying /nnnn =3 the file compare will halt at the 4th line (files too different)
Specifying /LB1 the file compare will halt after the first line

# Oh lord won't you buy me a Mercedes Benz, my friends all drive Porsches, I must make amends # - Janice Joplin

Related:

Q953929 - FC.exe command does not work correctly in Windows XP when files differ on every 128th byte
COMP - Compare two files and display any characters which do NOT match
FIND - Search for a text string in a file
FINDSTR - Search for strings in files
WinDiff - GUI to compare files
Powershell: Compare-Object - Compare the properties of objects, e.g. compare content of files.
Equivalent bash command (Linux): cmp - Compare two files