Howto write good perl programs

(Or at least not making the same mistakes again and again).

Avoid creating circular memory references at all costs

Use modules like Devel::Cycle to check for circular references. And never do stuff like:

	$this->{stuff} = $this;
	

Bad examples of code that does this are Mail::SpamAssassin, Mail::Audit (now unmaintained), etc.

Try to use the /o modifier in regular expressions as much as possible.

So the regex is only compiled once. This can't be done when the regex depends on a variable, like in:
m/some stuff \d $text/
So it's better to make regex static whenever possible. Even if you have to check against a group of regexps.

Filenames end at the end of string, not in newline

This is bad: $filename =~ m/^stuff this and that$/o # check if filename is "stuff this and that". *WRONG*
Filename could be: "stuff this and that\n" and "stuff this and that". Newline is a valid character in filenames.

While this is good: $filename =~ m/\Astuff this and that\z/o

Also filenames can have spaces and regexp metacharacters, so if you have the filename stored in a variable and want to check that in a regex, disable metacharacters before the variable read on.

Be careful with regexp interpolation

As I was saying previously, a filename like:
$fname = "stuff priced at 50.xml"; When used in a regex like:
$file =~ m/\A$fname\z/;
Would match "stuff priced at 509xml" and "stuff priced at 50-xml", so you have to do it like:
$file =~ m/\A\Q$fname\E\z/

Use "strict" and "warnings" when your program grows more than 25 lines

Use it early and keep your code clean. Reduce the use of global variables.