Diff

On unix systems find differences between 2 files

diff file1 file2

Show differences between the 2 files

diff -b file1 file2

Ignore space changes

diff -u file1 file2

diff -U <num> file1 file2

Report all differences between the files

Lines starting with < (-) need to be removed and starting with > (+) need to be added to go from file1 to file2

-u -U also report some lines before and after the actual difference (the context) (default 3) with -U <num> you can specify the number of context lines.