DCPM: perltutopen blues....

[Matthew Browning]

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On Friday 04 July 2003 23:37, Simon Waters wrote:
> Thanks, I think I was just getting confused with the documentation.
> I'm still slightly vague on when perl is doing file handles, and when
> it is expecting file names... When they look vaguely like good old
> fashioned Bourne shell file handles all is clear.
>

Perl filehandles look pretty much the same as in C.  The ones you are 
dealing with are hidden behind two layers of obscurity.  First, your 
module takes a filename as an argument and manipulates the filhandle 
internally, second it does so by means of the IO::File (standard) 
module.

FWIW, I typically use IO::File because it allows you to treat a 
filehandle as a scalar (by returning a reference to one) which is cool 
if you want a painless way to build an array of them or chuck them 
around various functions etc.


> My script has gained a plethora of "options", including the
> ubiquitous "--debug" ;-)
>
> Maybe trying to learn emacs and perl at the same time was a bit
> ambitious, but it will be the best indented code I've written in
> ages.
>

They make a good team:

C-x h C-u M-| perl -pe 'EXPR' (Mark Jason Dominus)

...I have bound F12 to a Lisp function that runs the script I am 
working on, diplaying the output in a new buffer. That is quite handy.  
Also, check out M-x cperl-perldoc for context-specific help.  Use 
cperl-mode, not the default perl-mode with GNU Emacs.


> Next fun bit will be a signal handler, it all looks simple("use
> sigtrap" ?), but I never seen to find any example scripts - maybe I
> should squander another book token. Hmm 15GBP book tokens, 10GBP
> extra if WH Smiths... I'll go check the review section.
>

I guess the Camel is your best bet.  I have read pretty much all the 
books there are on Perl (seriously) and if there is one that really 
made me think *wow* it is `Object-Oriented Perl' by Damien Conway 
(Manning).  Having said that, it does not address your problem.

> Then ensuring it is self documenting.... 

$ perldoc perlpod

> then sorting the output
> routines, and I'll be ready to fix the special cases...
>
...
> Why does "use warnings" dislike "@array[2]" and suggest "$array[2]",
> seems less clear to me, or am I missing something elementary?


The first is an array slice, the second an array element.  While 
contrary to the conventions we see in other languages, Perl wants you 
to refer to a scalar as a scalar, even if it is an element of an array. 
 The first is a list, albeit with one element.

Just keep telling yourself: `it all makes perfect sense'...


Matthew Browning.



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