Re: [MacPerl-Scribes] "Basic Perl Filters in BBEdit" Column

[Brian McNett <webmaster@mycoinfo.com>]

AT&F1&K3&W
OK

Jim Correia said in Re: [MacPerl-Scribes] "Basic Perl Filters in BBEdit" 
Colum at Apr/19/2000, Wed 13:30:03.

> Here is quickie example that reverses the selected lines.  If it looks
> like C it is because I write C all day long and it influences my perl
> (of which I don't do or know too much):
> 
> #!perl -w
> use strict;
> 
> while ( <> )
> {
>     my $s = $_;
>     
>     chomp($s);
>     
>     my $ct = length($s);
>     
>     for(my $i=$ct-1; $i>=0; $i--)
>     {
>         print substr($s, $i, 1);
>     }
> 
>     print "\n";
> }

Yup, looks like a C programmer wrote it. ;-) Yes, I'm still here.  
Snail-mail hasn't arrived with my memory yet, and the local parts place 
(where I can get a 28.8K modem for $6) just now opened for the day.  Jim's 
script is a good case study on using #! switches. Perl also does advanced 
string handling far better than C (which as I recall doesn't actually *do* 
string handling, but I never got anywhere close to understanding C), so a 
simple:

#!perl -pl
$_ = reverse

does the same thing.  This kinda stuff happens on BBEdit-Talk a lot, seeing 
as Perl is a second language to a many programmers.  Jim's version also 
works, BTW, with much re-invention of the wheel. ;-)  I'm not, conversely, 
able to hold my own on *his* ground, so this says nothing against Jim.  I'd 
be at a complete loss in C  (C being one of the fifteen "Seven programming 
languages I failed to become proficient in before learning Perl"), so that 
Jim's script runs, and works as expected is either a tribute to Perl or Jim 
or both.

Now perhaps, since I'm online at the moment, I can explain how to get from 
Jim's example to mine:

First, note that the entire script is encased in a while().  This calls for 
either -p or -n on the hash-bang to remove that construction.  Second, note 
that the while() ends with a print().  This makes it -p without a doubt.

Third, note that the script chomp()s input and appends "\n" to its output.  
Assigning  $_ to $s is an uncessary step.  It's more idiomatically perlish 
to just "chomp;", which performs chomp($_) by default, thus dropping $s 
from the namespace.  This calls for -l, thus removing both chomp() and 
print().

Since the purpose of the for() loop is duplicated by the built-in function 
reverse(), and reverse applies to $_ by default, the entire for loop 
becomes "$_ = reverse", and all the associated variables are dropped from 
the namespace.  The idiomatic version is **trivially** faster and less 
memory intensive.  In practice, both versions are too fast to time.

+++
NO CARRIER


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