在UNIX系统中,Shell程序(21)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:$$
B.echo UserHome directory:$HOME echo Current shell'PID:$@
C.echO UserHOme directOIy:$LOGNAME echo Current shell'sPID:$@
D.echo UserHome directory:$HOME echo Current shell'sPID:$$