|Perl: the Markov chain saw|
Comment on http://www.tizag.com/perlT/by blazar (Canon)
|on Oct 03, 2007 at 23:41 UTC||Need Help??|
At the request of Lady_Aleena I'm duplicating here some comments to excerpts from a site she had been somewhat naively "advertising". (In the original they've now been put in spoiler tags.) Perhaps someone may want to add further comments, since my reply was buried deep enough in the original thread not to have much visibility.
This tutorial will be covering the PERL syntax and should provide you with a very solid foundation of PERL for you to build upon.
There's Perl and there's perl, but not such a thing as PERL. This is even the subject of a faq entry. Please notice that this may seem a very lightweight flaw to you but as you can read e.g. in PERL as shibboleth and the Perl community it is much used in Perl circles to tell who's in the know from who is not, and it's not a matter of elitist attitude, trust me: whoever wrote that doesn't know Perl but in possibly a very superficial manner and I wouldn't want read on the site, but let's go on...
The language is very simplistic, offering optimum flexibility, perfect for short, straightforward scripting.
I can't see how one could claim Perl to be simplistic: it is often alleged to be awkwardly complex instead...
First things first, you must have PERL 5.005 installed on your web hosting machine. Version 5.005 is available for download via Perl.com, just follow the download links.
It's dealing with 5.005 and while Perl is mostly backwards compatible, this detail clearly shows that the tutorial is at best seriously outdated.
Regardless of the program you choose to use, a PERL file must be saved with a .pl (.PL) file extension in order to be recognized as a functioning PERL script.
Where? Why? How so? Funnily enough the "tutorial" is strongly geared at *NIX audience, where the concept of "extension" is even non-existant. And as far as the web server is concerned, it's all up to its configuration, but that claim with "must" is plainly wrong and misleading.
File names can contain numbers, symbols, and letters but must not contain a space. Use an underscore (_) in places of spaces.
Where? Why? How so? While I don't particularly like spaces in filenames, especially in programs, most modern enough osen can happily deal with them, from *NIX where anything but "\0" and "/" can be used, to Win where they're actually abused. So what?
Personally, however web-oriented the tutorial may be, I would introduce
and -T early. Good programming practices are good programming practices everywhere, even more where security matters...
Another great debugging technique is to isolate the code you are currently working on. To do this you can temporarily comment out lines of code to isolate only the section that is returning an error message.
Comments are necessary for any script you wish to publish to others or make readily available.
Not necessarily. Well crafted, self explaining code with proper POD documentation could happily have very few to no comments at all.
Whoa! What a nice practice to advertise...
In PERL we use the backslash (\) character to escape any type of character that might interfere with our code. For example there may become a time when you would like to print a dollar sign rather than use one to define a variable. To do this you must "escape" the character using a backslash (\).
Not in "PERL". In double quoted strings. Because he should say, first, that those strings interpolate variables. Outside of a string, the backslash befor a dollar sign has an entirely different meaning.
The latter example using the my parameter is another means to define a variable that you might run across as you gain more experience. It is not necessary to use the my parameter. Variables can be defined either way.
Funny: I had never heard anyone call my a "parameter"! Anyway, he who writes shows not to have understood what it is all about and if by any chance he/she did, then he's still giving that impression.
Scalar variables are simple variables containing only one element--a string or a number. Strings may contain any symbol, letter, or number.
No, they can contain much more.
Notice that we used a period (.) between each of our variables. This is a special kind of operator that temporarily appends one string to another.
"Temporarily"? Also, the IMHO bad example with print will get some people into the habit of always using the concatenation operator.
Numbers are scalar data. They exist in PERL as real numbers, float, integers, exponents, octal, and hexidecimal numbers.
Not exactly: some confusion between ways to specify numbers, and numbers.
Logical operators state and/or relationships. Meaning, you can take two variables and test an either or conditional. Logical operators are used later on in conditionals and loops. For now, just be able to recognize them in the upcoming examples.
Funnily enough, he mentions numeric and stringwise comparison operators at a time, in a table, without specifying in what they differ and thus giving the impression that e.g. > and ge are equivalent. To be sure, it claims that 7 ge 11 is a false value. But it is true!!!
There are two ways to set an array to scalar mode. We can use the scalar() function or we can redefine the array as a scalar variable.
Ok, I grew tired and I'm stopping here, but I'm sure there are quite a lot of other "gems"...