emailing diff output between two files only if there is a difference

How can I email the output between file1 and file2 but only if there is a difference? Lets say I’m using a shell script.

diff file1 file2 | mail -s "subject" "[e-mail]"

Answer

Use the || concatenation.

diff -q file1 file2 || diff file1 file2 | mail -s "subject" "[e-mail]"

More info here