Intro to Perl Programming - Day 4

Goals

• learn to use DBM hashes
• use file testing and directory ops
• use a simple object-oriented module

POST

• What are some differences between these two statements:
  $someVar = <DATA>;
@someVar = <DATA>;
• What are some differences between these two statements:
  $someVar = $array[0];
$someVar = @array[0];
• Spot the bug:

  
  format _TOP =
  @>>
  $id
  
  

• Spot the bug:print("The chicken says "bock! bock! bock");
• Spot the bug:@result = split(/:/, 'Mario;555-1212;Dayton, OH');
• What does this syntax do? qq//
• What does this symbol indicate? $
• What does this symbol indicate? @
• What does this symbol indicate? %
• What does this symbol indicate? &

learn to use DBM hashes

• dbmopen(%hash, [dbm_name], [mode]);
• dbmclose(%hash);
• two-field workaround: compound value, ie: $office{11981}="John Price:1100 Elm Street:blah:foo:bar";

use file testing and directory ops

• file testing for control structures: (-x [filename] ). See chart on 113
• opendir(HANDLE, "path");
• @filenames=readdir(HANDLE);
• close(HANDLE);

use a simple object-oriented module - subroutine style

[perldoc Trig]
NAME
Math::Trig - trigonometric functions
        
SYNOPSIS
use Math::Trig;
	        
$x = tan(0.9);
$y = acos(3.7);
$z = asin(2.4);
							      
$halfpi = pi/2;
				      
$rad = deg2rad(120);

use a simple object-oriented module - method style

[perldoc Ping]
NAME
Net::Ping - check a remote host for reachability
        
SYNOPSIS
use Net::Ping;
		    
$p = Net::Ping->new();
print "$host is alive.\n" if $p->ping($host);
$p->close();
						      
$p = Net::Ping->new("icmp");
foreach $host (@host_array)
	{
	print "$host is ";
	print "NOT " unless $p->ping($host, 2);
	print "reachable.\n";
	sleep(1);
        }
$p->close();

...


 Net::Ping->new([$proto [, $def_timeout [, $bytes]]]);      
Create a new ping object.  All of the parameters are
optional.  $proto specifies the protocol to use when
doing a ping.  The current choices are "tcp", "udp" or
"icmp".  The default is "udp".

...

$p->ping($host [, $timeout]);
Ping the remote host and wait for a response.  $host
can be either the hostname or the IP number of the
remote host.  The optional timeout must be greater
than 0 seconds and defaults to whatever was specified
when the ping object was created.  If the hostname
cannot be found or there is a problem with the IP
number, undef is returned.  Otherwise, 1 is returned
if the host is reachable and 0 if it is not.  For all
practical purposes, undef and 0 and can be treated as
the same case.

looking ahead (optional material)

1. references
   • to scalars
   • to arrays
   • to hashes
   • to subroutines and typeglobs
   • anonymous scalars, arrays, and hashes
2. symbolic references
3. Something.pm
4. packages (namespace), exporting
5. modules (reusable units of code)
6. class objects

Conclusion

Where to go from here

• Grab a perl interpreter
• perl 2
• debugger, profiler
• use Modules;
• write your own function libraries and modules