Embedding Perl in HTML with Mason

This book is available for free @_ http://www.masonbook.com/book/

Perl Inheritance Simplified

http://perl.active-venture.com/pod/perltoot-inheritance.html

Perl Special Literals list

__FILE__ = represent the current filename
__LINE__ = line number
__PACKAGE__ package name

If there is no current package (due to an empty package; directive),
__PACKAGE__ is the undefined value.

The two control characters ^D and ^Z, and the tokens __END__ and __DATA__ may be used to indicate the logical end of the script before the actual end of file. Any following text is ignored.

Text after __DATA__ may be read via the filehandle PACKNAME::DATA, where PACKNAME is the package that was current when the __DATA__ token was encountered. The filehandle is left open pointing to the contents after __DATA__. It is the program's responsibility to close DATA when it is done reading from it. For compatibility with older scripts written before __DATA__ was introduced, __END__ behaves like __DATA__ in the top level script (but not in files loaded with require or do) and leaves the remaining contents of the file accessible via main::DATA.

See SelfLoader for more description of __DATA__, and an example of its use. Note that you cannot read from the DATA filehandle in a BEGIN block: the BEGIN block is executed as soon as it is seen (during compilation), at which point the corresponding __DATA__ (or __END__) token has not yet been seen

How to determine Total memory (Total RAM, Used RAM, Free RAM) on Unix/Linux

'free' tool prints pretty much everything.

total used free shared buffers cached
Mem: 514592 274136 240456 0 20228 134104
-/+ buffers/cache: 119804 394788
Swap: 1052216 0 1052216

or

cat /etc/meminfo - has all the information.

How to find out which process is listening upon a port

For standard processes, Services names can be seen in /etc/services files associated with port numbers. This is pretty much standard TCP/IP.

For non-standard user defined services,

lsof -i :port_number

For example:

So to see which process is listening upon port 80 we can run:

root@mystery:~# lsof -i :80
This gives us the following output:

COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
apache2 10437 root 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 10438 www-data 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 10439 www-data 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 10440 www-data 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 10441 www-data 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 10442 www-data 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 25966 www-data 3u IPv6 22890556 TCP *:www (LISTEN)
apache2 25968 www-data 3u IPv6 22890556 TCP *:www (LISTEN)