if [ ! -e /tmp/ ]   #-e 为检测目录或文件是否存在  ！为取反

    then

         mkdir -v /tmp/

         echo 'ok'

 fi

 if [ $USER == 'root' ]

   then

     echo 'hey admin'

 else

     echo 'hey user'

 fi

if [ $ -eq $ ]  #$1 $2 为传参后的变量

   then

        echo "$1 eq $2"

elif [ $ -le $ ]

   then

        echo "$1 lesseq $2"

else

   echo "$1 greateq $2"

fi

if (( /+> ));then

    echo 'yes'

else

    echo 'no'

fi

for i in r1 rr1 ra1 abc

  do

     if [[ $i = r* ]];then

        echo $i

     fi

done