在UNIX系统中,Shell程序( )实现显示用户主目录以及当前命令的进程标识符。
A、echo UserHome directory: $LOGNAME
echo Current shell’s PID: $$
B、echo UserHome directory: $HOME
echo Current shell’s PID: $@
C、echo UserHome directory: $LOGNAME
echo Current shell’s PID: $@
D、echo UserHome directory: $HOME
echo Current shell’s PID: $$