using and (&&) operator in if statement bash script -

i have 3 variables:

var1="file1" var2="file2" var3="file3" 

how use , (&&) operator in if statement this:

if [ -f $var1 && -f $var2 && -f $var3 ]    ... fi 

when write code gives error. right way?

so make expression work, changing && -a trick.

it correct this:

 if [ -f $var1 ] && [ -f $var2 ] && [ -f $var3 ]   .... 

or like

 if [[ -f $var1 && -f $var2 && -f $var3 ]]   .... 

or even

 if [ -f $var1 -a -f $var2 -a -f $var3 ]   .... 

you can find further details in question bash : multiple unary operators in if statement , references given there what difference between test, [ , [[ ?.