Questions[bash](server)

What are the functional differences between the .profile, .bash_profile and .bashrc files?

How do I get the current Unix time in milliseconds (i.e number of milliseconds since Unix epoch January 1 1970)?

I need to get a list of human readable du output.

However, du does not have a "sort by size" option, and piping to sort doesn't work with the human readable flag.

For example, running:

du | sort -n -r 

Outputs a sorted disk usage by size (descending):

du |sort -n -r
65108   .
61508   ./dir3
2056    ./dir4
1032    ./dir1
508     ./dir2

However, running it with the human readable flag, does not sort properly:

du -h | sort -n -r

508K    ./dir2
64M     .
61M     ./dir3
2.1M    ./dir4
1.1M    ./dir1

Does anyone know of a way to sort du -h by size?

I just wondered what exactly the difference between

[[ $STRING != foo ]]

and

[ $STRING != foo ]

is, apart from that the latter is POSIX-compliant, found in sh and the former is an extension found in bash.

What is the best way to determine if a variable in bash is empty ("")?

I have heard that it is recommended that I do if [ "x$variable" = "x" ]

Is that the correct way? (there must be something more straightforward)