shell脚本：

#!/bin/bash

if [ $USER == "root" ];then
   yum -y install vsftpd
else
   echo "You are not root account,installing software is not needed."
fi

OR

#!/bin/bash

if [ $UID -eq 0 ];then
   yum -y install vsftpd
else
   echo "You are not root account,installing software is not needed."
fi

shell脚本运行：

root-1.sh

[root@elasticsearch ~]# sh root-1.sh 
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
CentOS7                                                                             | 3.6 kB  00:00:00     
Resolving Dependencies
--> Running transaction check
---> Package vsftpd.x86_64 0:3.0.2-28.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

===========================================================================================================
 Package                Arch                   Version                       Repository               Size
===========================================================================================================
Installing:
 vsftpd                 x86_64                 3.0.2-28.el7                  CentOS7                 172 k

Transaction Summary
===========================================================================================================
Install  1 Package

Total download size: 172 k
Installed size: 353 k
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : vsftpd-3.0.2-28.el7.x86_64                                                              1/1 
  Verifying  : vsftpd-3.0.2-28.el7.x86_64                                                              1/1 

Installed:
  vsftpd.x86_64 0:3.0.2-28.el7                                                                             

Complete!
[root@elasticsearch ~]#

root-2.sh

[root@elasticsearch ~]# sh root-2.sh 
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package vsftpd.x86_64 0:3.0.2-28.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

===========================================================================================================
 Package                Arch                   Version                       Repository               Size
===========================================================================================================
Installing:
 vsftpd                 x86_64                 3.0.2-28.el7                  CentOS7                 172 k

Transaction Summary
===========================================================================================================
Install  1 Package

Total download size: 172 k
Installed size: 353 k
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : vsftpd-3.0.2-28.el7.x86_64                                                              1/1 
  Verifying  : vsftpd-3.0.2-28.el7.x86_64                                                              1/1 

Installed:
  vsftpd.x86_64 0:3.0.2-28.el7                                                                             

Complete!
[root@elasticsearch ~]#