GNU DIFFUTILS is a set of utilities used to compare files for differences.

cmp:
The cmp utility compares two files. cmp will write no output if the files are the same. Under default options, if they differ, it writes to standard output the byte and line numbers at which the first difference occurred. Bytes and lines are numbered beginning with 1. If one file is an initial subsequence of the other, that fact is noted. skip1 and skip2 are initial byte offsets into file1 and file2 respectively, and may be either octal or decimal; a leading 0 denotes octal.

diff:
The diff utility will compare the contents of file1 and file2 and write to standard output a list of changes necessary to convert file1 into file2.

diff3:
diff3 compares three versions of a file, and publishes disagreeing ranges of text flagged with these codes:

==== all three files differ

====1 filename1 is different

====2 filename2 is different

====3 filename3 is different

patch:
The patch command reads a source (patch) file containing any of the three forms of difference (diff) listings produced by the diff(1) command (normal, context or in the style of ed(1)) and apply those differences to a file. By default, patch reads from the standard input.

sdiff:
sdiff uses the output of the diff command to produce a side-by-side listing of two files indicating lines that are different.