I saw a code today that went like:

if (-e ...) {

}

what is the -e for??

"-e" is a boolean operator; it returns a true value if the following expression  evaluates to the name of an object which can be seen by your perl program to exist on the file system.   Put rather more colloquially, it checks whether a file exists (but that's a loose definition as it will return true for a directory, a named pipe, a device, or any other object ... and it may return false if a file does exist, but can't be seen because it's in a directory that can't be read by your program).

Other similar operators that you'll often use include
-f      is it a plain file
-d      is it a directory
-z      is it an empty file
-r      can I read the contents of ...
-w      can I write to ...

Further operators that follow the same structure return something rather more than just a "yes/no" response - for example
     print -s "/usr/bin/perl"
will print out the size in bytes of your perl executable and
     $age = -M "index.html"
will set $age to be the number of days ago (yes, it will have a decimal part) that the index.html file in the current directory was modified

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