Check file existence

You check file existence using test command.

if test ! -s "dirname/filename"
then
 echo "File does not exist"
else
 echo "File exists"
fi

Here is the alternative way to check file existence. You can also check for multiple files

if [ -f dirname/filename1 ] && [ -f dirname/filename2 ]
then
 echo "File exists"
else
 echo "File does not exist"
fi