Technically, there's no difference between for and foreach other than some style issues.
One is an alias of another. You can do things like this
foreach (my $i = 0; $i < 3; ++$i)
  { # normally this is foreach print $i, "n";}
  for my $i (0 .. 2)
  { # normally this is for print $i, "n";}
 - exec runs the given process, switches to its name and never returns while system forks off the given process, waits for it to complete and then returns.

 Files are opened using the open and sysopen function. Either function may be passed up to 4 arguments, the first is always the file handle thenfile name also known as a URL or filepath, flags, and finally any permissions to be granted to this file.
  $FH = "filehandle";
 $FilePath = "myhtml.html";
  open(FH, $FilePath, permissions);
or
 sysopen(FH, $FileName, permission);

 $ indicate scalar data type

 @ indicates an array and

 % indicates an hash or an associative array.

 we will get a no.of modules from CPAN, there so many module for database interface, database drivers.
to do the mathematical operations ,text processing .
each module is to handle a small tasks .

 My Favourite module is CGI.pm Bcoz it can handle almost all the tasks like
1. parsing the form input
2. printiing the headers
3. can handle cookies and sessions and much more

In the HTML form, you have to mention the perl script name.
Ex: <form action="test.pl" method="POST">. Then in the test.pl, you have to mention the content-type as print "content-type: text/html\n\n";. And read the form values and print them.

 It is having the features of scripting(shell) as well as programming(like c). Using perl u can easily do the system administration works where comparitively difficult with shell script.

 $str='Hello';
 $cnt= ($str=~s/l/i/g);
 print $cnt;
  $cnt stores the number of replacements.