test command

do:  man test
NAME
       test - check file types and compare values

SYNOPSIS
       test EXPRESSION
       test

       [ EXPRESSION ]
       [ ]
       [ OPTION





 -a:
                                                                                                                                     EXPRESSION1 -a EXPRESSION2
    both EXPRESSION1 and EXPRESSION2 are true

-f : FILE
              FILE exists and is a regular file
 -x FILE
              FILE exists and execute (or search) permission is granted