REDIRECTIONS

0             stdin
1             stdout
2             stderr

<&-           close stdin
>&-           close stdout
<>filename    open filename for read-write
2>&1          open 2 for write and dup as 1

Examples:
  cmd 2>/dev/null
  cmd >/dev/null 2>&1
  exec 1<&-           # close descriptor 1
  exec 2<&-           # close descriptor 2
  exec 1< /dev/null   # open descriptor 1
  exec 2< /dev/null   # open descriptor 2