如何在awk中获得系统输出？

awk '
  BEGIN {
    print "Before command execution:"
  }
  {
    cmd="ls -l"
    print $0 | "cmd"
  }
  END {
    print "After command execution:"
  }
'

awk '
  BEGIN {
    print "Before command execution:"
  }
  {
    cmd="cat /etc/passwd"
    print $0 | "cmd"
  }
  END {
    print "After command execution:"
  }
'