>> /dev/null
redirects standard output (stdout
) to /dev/null
, which discards it.
(The >>
seems sort of superfluous, since >>
means append while >
means truncate and write, and either appending to or writing to /dev/null
has the same net effect. I usually just use >
for that reason.)
2>&1
redirects standard error (2
) to standard output (1
), which then discards it as well since standard output has already been redirected.
转自: http://stackoverflow.com/questions/10508843/what-is-dev-null-21