Compares two files or sets of files and displays the differences between them.


fc /a [/c] [/l] [/lb<n>] [/n] [/off[line]] [/t] [/u] [/w] [/<nnnn>] [<drive1>:][<path1>]<filename1> [<drive2>:][<path2>]<filename2>
fc /b [<drive1:>][<path1>]<filename1> [<drive2:>][<path2>]<filename2>


Parameter Description
/a Abbreviates the output of an ASCII comparison. Instead of displaying all of the lines that are different, fc displays only the first and last line for each set of differences.
/b Compares the two files in binary mode, byte by byte, and does not attempt to resynchronize the files after finding a mismatch. This is the default mode for comparing files that have the following file extensions: .exe, .com, .sys, .obj, .lib, or .bin.
/c Ignores the letter case.
/l Compares the files in ASCII mode, line-by-line, and attempts to resynchronize the files after finding a mismatch. This is the default mode for comparing files, except files with the following file extensions: .exe, .com, .sys, .obj, .lib, or .bin.
/lb<n> Sets the number of lines for the internal line buffer to N. The default length of the line buffer is 100 lines. If the files that you are comparing have more than 100 consecutive differing lines, fc cancels the comparison.
/n Displays the line numbers during an ASCII comparison.
/off[line] Doesn't skip files that have the offline attribute set.
/t Prevents fc from converting tabs to spaces. The default behavior is to treat tabs as spaces, with stops at each eighth character position.
/u Compares files as Unicode text files.
/w Compresses white space (that is, tabs and spaces) during the comparison. If a line contains many consecutive spaces or tabs, /w treats these characters as a single space. When used with /w, fc ignores white space at the beginning and end of a line.
/<nnnn> Specifies the number of consecutive lines that must match following a mismatch, before fc considers the files to be resynchronized. If the number of matching lines in the files is less than nnnn, fc displays the matching lines as differences. The default value is 2.
[<drive1>:][<path1>]<filename1> Specifies the location and name of the first file or set of files to compare. filename1 is required.
[<drive2>:][<path2>]<filename2> Specifies the location and name of the second file or set of files to compare. filename2 is required.
/? Displays help at the command prompt.


  • This command is implemented by c:\WINDOWS\fc.exe. You can use this command within PowerShell, but be sure to spell out the full executable (fc.exe) since 'fc' is also an alias for Format-Custom.

  • When you use fc for an ASCII comparison, fc displays the differences between two files in the following order:

    • Name of the first file

    • Lines from filename1 that differ between the files

    • First line to match in both files

    • Name of the second file

    • Lines from filename2 that differ

    • First line to match

  • /b displays mismatches that are found during a binary comparison in the following syntax:


    The value of XXXXXXXX specifies the relative hexadecimal address for the pair of bytes, measured from the beginning of the file. Addresses start at 00000000. The hexadecimal values for YY and ZZ represent the mismatched bytes from filename1 and filename2, respectively.

  • You can use wildcard characters (* and ?) in filename1 and filename2. If you use a wildcard in filename1, fc compares all the specified files to the file or set of files specified by filename2. If you use a wildcard in filename2, fc uses the corresponding value from filename1.

  • When comparing ASCII files, fc uses an internal buffer (large enough to hold 100 lines) as storage. If the files are larger than the buffer, fc compares what it can load into the buffer. If fc doesn't find a match in the loaded portions of the files, it stops and displays the following message:

    Resynch failed. Files are too different.

    When comparing binary files that are larger than the available memory, fc compares both files completely, overlaying the portions in memory with the next portions from the disk. The output is the same as that for files that fit completely in memory.


To make an ASCII comparison of two text files, monthly.rpt and sales.rpt, and display the results in abbreviated format, type:

fc /a monthly.rpt sales.rpt

To make a binary comparison of two batch files, profits.bat and earnings.bat, type:

fc /b profits.bat earnings.bat

Results similar to the following appear:

00000002: 72 43
00000004: 65 3A
0000000E: 56 92
000005E8: 00 6E
FC: earnings.bat longer than profits.bat

If the profits.bat and earnings.bat files are identical, fc displays the following message:

Comparing files profits.bat and earnings.bat
FC: no differences encountered

To compare every .bat file in the current directory with the file new.bat, type:

fc *.bat new.bat

To compare the file new.bat on drive C with the file new.bat on drive D, type:

fc c:new.bat d:*.bat

To compare each batch file in the root directory on drive C to the file with the same name in the root directory on drive D, type:

fc c:*.bat d:*.bat