What does the @ in ls -al mean?
When doing an ls -l some files are tagged with "@" like this:
-rw-r--r--@ 1 master staff 2074042 Feb 3 19:26 openssh-5.1p1-vs-openbsd.diff
What does that mean?
They are extended attributes. ls -l@ shows them (mostly they are flags to indicate that the file is coming from the internet, in those cases, when opening the file (or installing a DMG) MacOS will ask if you really want to open it). The xattr command allows you to change them.
There is another one too. ls -lO (upper case O) shows the flags set via chflags command. ls -lO@ shows the file in it's full glory.