Package diffutils

A GNU collection of diff utilities

http://www.gnu.org/software/diffutils/diffutils.html

Diffutils includes four utilities: diff, cmp, diff3 and sdiff. Diff
compares two files and shows the differences, line by line. The cmp
command shows the offset and line numbers where two files differ, or
cmp can show the characters that differ between the two files. The
diff3 command shows the differences between three files. Diff3 can be
used when two people have made independent changes to a common
original; diff3 can produce a merged file that contains both sets of
changes and warnings about conflicts. The sdiff command can be used
to merge two files interactively.

Install diffutils if you need to compare text files.

General Commands
Command Description
cmp compare two files byte by byte
diff compare files line by line
diff3 compare three files line by line
sdiff side-by-side merge of file differences