The perl binary aquires memory for the perl program but this memory is never released to the operating system as long as the perl program runs.

So inside a running program the memory is reused but never freed.

Dear busunl ,
Do you meant to say that each perl program will consume their required memory when it starts ?
One more question is whether it acquires more memory during run time

It does not acquire all memory when it starts.

It will get more memory during runtime when needed.

There are two major points in perl memory management:

1. You don't have to bother, perl will do that for you
2. Memory will not be freed during runtime

That's all.

As other Monks have answered the main bit of your question i.e. the memory is 'freed' but not 'released' - one tip that i have found useful for when i really do need to release memory is to separate the work of into a child process, and when this process finishes the memory really will be cleared. Introduction to Parallel::ForkManager may help you with this.

Some other useful stuff if you want to find out more:

Hope this helps

It depends upon the version and platform of Perl.

Under Windows, perl can and does release some memory back to the OS when it is done with it, as demonstrated below:

c:\test>p1
Name "Data::Dump::MAX_WIDTH" used only once: possible typo at C:\Perl6
+4\bin\p1.p
[0] Perl> system qq[ tasklist /fi "pid eq $$"];;

Image Name                     PID Session Name        Session#    Mem
+ Usage
========================= ======== ================ =========== ======
+======
perl.exe                      5600 Console                    1      9
+,972 K
[0] Perl> $big = 'x' x 10e6;;
[0] Perl> system qq[ tasklist /fi "pid eq $$"];;

Image Name                     PID Session Name        Session#    Mem
+ Usage
========================= ======== ================ =========== ======
+======
perl.exe                      5600 Console                    1     19
+,764 K
[0] Perl> undef $big;;
[0] Perl> system qq[ tasklist /fi "pid eq $$"];;

Image Name                     PID Session Name        Session#    Mem
+ Usage
========================= ======== ================ =========== ======
+======
perl.exe                      5600 Console                    1      9
+,976 K
[download]

And I've heard tell, but cannot verify that under some circumstances, Perl will do the same on some other platforms. YMMV.

But in the end, it is irrelevant, and your trainers should be taken to task for even mentioning it at your stage of learning.

Does the trainer mean that other comparible languages behave in a differnt way? That is the implication of the question.

I would, personally, not imply something which hasn't been asked, but indeed maybe an even more interesting question would be: Is there ANY modern (i.e. post-C++) language at all which does NOT handle memory allocation automatically? I don't talk about ongoing developments in "old" languages (such as FORTRAN, C or COBOL), or newer ones which for compatibility reason have to carry some burden from an older language (such as C++).

-- 
Ronald Fischer <ynnor@mm.st>

From the viewpoint of language definition of Perl, there is nothing which dictates that memory must be reused, though an implementation of Perl, which does not free memory, would hardly be useful except for the most simple tasks. So I would say: The question whether "Perl" (as a language) reuses memory, is meaningless, but all existing Perl implementations certainly re-use memory. Of course this does not mean that part of the memory not used by Perl, automatically can be used by other application. This question belongs to the architecture of the undrelying OS, and is not related to Perl.

can't I free a memory and assign to some other ?

my $a='abcd';
...
$a='efgh';
[download]

Of course this does not mean that part of the memory not used by Perl, automatically can be used by other application. This question belongs to the architecture of the undrelying OS, and is not related to Perl.

That's not entirely true. Certainly, whether or not the OS is able to accept memory back from the OS isn't related to perl. But if perl runs on an OS that does allow for processes to return memory back to the OS during the lifetime of the process, then it becomes related to perl. Because then perl would actually have to make the appropriate system calls to give memory back.

then it becomes related to perl.

Thank you for clarification. To be more precise: It becomes related to the Perl implementation (not to Perl as a language), i.e. ActiveState Perl could do it one way and Strawberry Perl could do it another way.

-- 
Ronald Fischer <ynnor@mm.st>

Because then perl would actually have to make the appropriate system calls to give memory back.

Perl should just use standard free(3) function and this function will make appropriate system call to return memory to OS.