Hi NoobiePerlist. There is indeed a very good reason for that. Because the interpreter does not know what you are trying to do, it only does what you tell it to do. When i first started seriously programming back in 1996 (with C++ no less) i felt the same way. "What the heck does that mean?!?!?!" With C++, there is no interpreter, but instead a compiler. The principle is still the same though ... something reads your program one line at a time and attempts to do something with it. When you tell something to do an instruction it does not understand, that something tries very hard to tell you why it cannot. Unfortunately, until you learn what is really going on under that hood, you will not understand what something is trying to tell you.

My best advice to you is the same advice i give to my C++ lab students. First: code in small chunks - don't write an entire program first and then try to debug the entire thing. Instead, code a couple of lines and debug those - at least then you will be more likely to guess what really went wrong. Second: when you do have errors, focus on the first one - not the last one. Solve the first one and the others might just go away too.

Oh yeah - regarding this statement:

Registered members can always find their posts by going to their home node and clicking on the number next to the Writeups attribute. For example, here are yours . :)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

Hi NoobiePerlist,

As I know from the CB that you are using Windows and ActiveState Perl, you might like to try this. Cut and paste the first program below into Notepad and save it as play.pl

#!perl -w
$|++;$,=' ';
print $/,'perl> ';
eval($_) || print $@,$/
and print $/,'perl> ' while(<>);
[download]

Then open a CMD window and type "perl play.pl". You end up with a prompt that looks like this perl>. This will allow you to try out simple perl programs easily, and if you make a mistake, you can use the arrow keys to retrieve the line and edit it before trying again.

I've pasted a short example session below. Have fun!

C:\test>perl play.pl

 perl> print 'hello world!'
hello world!
 perl> $x = 100

 perl> $y = 10

 perl> print $x/$y
10
 perl> print $_, "\n" for 1 .. 10
1
2
3
4
5
6
7
8
9
10


 perl>
[download]

This is close to what you probably have in mind when saying "interactive Perl". Unfortunately, this one has some confusing behaviour with scopes, caused by the eval block:

 perl> $_ = 'Foo'; print;
Foo
 perl> print;
print;

 perl> my $a = 'Bar'; print $a;
Bar
 perl> print $a;
Use of uninitialized value in print at (eval 4) line 1, <> line 4.
[download]

Writing the same commands in a file scoped script would produce different results.

I think it might be better to go this way:
Write a testscript in your favorite text editor. It might look like this:

#!perl            # header
use warnings;     # enable warnings
use diagnostics;  # explain warnings
                  # code to test:
print "Hey world, I'm coming!!!\n";
[download]

Then you can save the script (e.g. "C:\test.pl"). Open your DOS command window and type in the following to run your script:

perl C:\test.pl
[download]

When your script succeeds, you can modify it (trying out something else), save it and run the command again.

Hope this helps, have a lot of fun with Perl!

^~Django
"Why don't we ever challenge the spherical earth theory?"

I tried to put myself in the place of a 13 y/o kid with no programming experience sitting at his Windows/ME machine staring at a screen that looked like:

C:\>perl
ashdahskjd
kajhsdakjshd
[download]

I am aware that play.pl has scoping problems, but once his copy of Programming Perl for Win32 arrives, he may arrive at the point where he knows what scoping is.

I also thought about what would happen if his "favorite editor" is Word.

C:\>perl test.pl
Can't open perl script "test.pl": No such file or directory

C:\>dir test.pl
 Volume in drive C has no label.
 Volume Serial Number is 8C87-E163

 Directory of C:\

File Not Found

C:\>dir test*
 Volume in drive C has no label.
 Volume Serial Number is 8C87-E163

 Directory of C:\

02/09/08  07:18a        <DIR>          test
02/09/08  05:16p                19,456 test.pl.doc
               2 File(s)         19,456 bytes
                            302,397,440 bytes free

C:\>perl test.pl.doc
Unrecognized character \xD0 at test.pl.doc line 1.

C:\>
[download]

---

Well It's better than the Abottoire, but Yorkshire!

Why all the effort? perl -wde1 and then just play on the prompt. :-) It also lacks the scoping problems Django mentioned.

Makeshifts last the longest.

Maybe this is a matter of taste, but I think the Perl debugger might be confusing for the newbie. It has its own commands and doesn't execute programs the way they would normally run. Learning one thing after another, not all simultaneously is very important. I'd start with the most essential features and move on to the "specials" later. But as always, TMWTDI -- so check it out.

^~Django
"Why don't we ever challenge the spherical earth theory?"

C:\>perl -wde1
Default die handler restored.

Loading DB routines from perl5db.pl version 1.07
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(-e:1):   1
  DB<1>
[download]

"Ah! Help!"

  DB<1>h
T               Stack trace.
s [expr]        Single step [in expr].
n [expr]        Next, steps over subroutine calls [in expr].
<CR>            Repeat last n or s command.
r               Return from current subroutine.
c [line|sub]    Continue; optionally inserts a one-time-only breakpoin
+t
                at the specified position.
l min+incr      List incr+1 lines starting at min.
l min-max       List lines min through max.
l line          List single line.
l subname       List first window of lines from subroutine.
l $var          List first window of lines from subroutine referenced 
+by $var.
l               List next window of lines.
-               List previous window of lines.
w [line]        List window around line.
.               Return to the executed line.
[download]

"Um!"

Read more... (8 kB)

If you are purchasing "Programming Perl" (which I feel would be a wise choice once you have devoured "Learning Perl") you will find a marvelous section in the back of the book which catalogs many of the incomprehensible errors that you can receive.

Perl is, pretty much, designed to be fed a whole program and it will then attempt to interperet it. I remember the first Perl program that I wrote on my own. I typed and consulted references until I was sure that I had written a nice little command line based mailer that did only what I wanted. I ran the program and did not receive any useful error. Rather, I saw something along the lines of "You fool! You managed to core dump perl!"

Needless to say, I was astonished. But I have learned through trial and error, over the past two years, a bit more about coding. I cannot agree with my fellow monks enough: code in snippets.

A great thing I figured out is this: If you can contain some code in a subroutine (which you'll find out about soon enough) you can run it as a separate program. By breaking your code down into the smallest logical components you can think of, you can test them as small programs and then bring them back into the whole. This will let you test the functionality of each piece and you can learn where to look for errors.

Best of luck to you, and don't get disheartened by the learning curve. We've all gone through it, and are all willing to help as much as we can.

Your posts will appear lost unless you are looking the "Newest Nodes" section. Sometimes they might not appear for a while, depending on how long you have caching set for. But that's just a good guess on my part.

When you install ActivePerl on Windows, the default setting is to associate the .pl extension with perl.exe. When you double click a .pl file in explorer, windows opens a cmd window, runs the script and closes the window. I don't find this very useful and I know a lot of newbies find it confusing (error messages flash up and disappear).

I recommend associating .pl with your favourite editor instead (I'll refrain from making a recommendation).

I also recommend installing Micorosoft's Power Toys. Specifically the doshere.inf which allows you to right click on a folder in explorer and select 'Open a command prompt here'.