Diff command in Unix is used to find the differences between files(all types). Since directory is also a type of file, the differences between two directories can easily be figure out by using diff commands. For more option use man diff on your unix box.
-b Ignores trailing blanks (spaces and tabs)
and treats other strings of blanks as
equivalent.
-i Ignores the case of letters. For example,
`A' will compare equal to `a'.
-t Expands <TAB> characters in output lines.
Normal or -c output adds character(s) to the
front of each line that may adversely affect
the indentation of the original source lines
and make the output lines difficult to
interpret. This option will preserve the
original source's indentation.
-w Ignores all blanks (<SPACE> and <TAB> char-
acters) and treats all other strings of
blanks as equivalent. For example,
`if ( a == b )' will compare equal to
`if(a==b)'.
and there are many more.