show a progress bar while copying

i did this more for the fact that sometimes it want to know what progress really large files are at.

this method does cause some overhead and is not as fast as just a regular cp, but who cares.

user $ pv ../test500M | dd of=../test/test500M
 500MB 0:00:13 [36.6MB/s] [==============================================>] 100%
1024000+0 records in
1024000+0 records out
524288000 bytes (524 MB) copied, 13.6377 s, 38.4 MB/s
user $ time cp ../test500M ../test/

real    0m9.524s
user    0m0.080s
sys     0m3.310s

in gentoo, just emerge -av sys-apps/pv
or grab the source here