if list; then list; [ elif list; then list; ] ... [ else list; ] fi
       The  if list is executed.  If its exit status is zero, the then list is executed.  Otherwise, each
       elif list is executed in turn, and if its exit status is zero,  the  corresponding  then  list  is
       executed  and  the command completes.  Otherwise, the else list is executed, if present.  The exit
       status is the exit status of the last command executed, or zero if no condition tested true.

check file types and compare values

-e FILE
       FILE exists

command language