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 (Section 1)
cmp
Compare two files byte by byte. The optional SKIP1 and SKIP2 specify the number of bytes to skip at the beginning of each file (zero by default). Mandatory...
diff
Compare FILES line by line. Mandatory arguments to long options are mandatory for short options too.
diff3
Compare three files line by line. Mandatory arguments to long options are mandatory for short options too.
sdiff
Side-by-side merge of differences between FILE1 and FILE2. Mandatory arguments to long options are mandatory for short options too.