Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Help a perl apprentice
Message-ID: <10101@jpl-devvax.JPL.NASA.GOV>
Date: 25 Oct 90 07:24:03 GMT
References: <18840001@hp-lsd.COS.HP.COM> <10080@jpl-devvax.JPL.NASA.GOV> <1990Oct25.063526.1571@vlsi-mentor.jpl.nasa.gov>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 43

In article <1990Oct25.063526.1571@vlsi-mentor.jpl.nasa.gov> dave@vlsi-mentor.jpl.nasa.gov (David Hayes) writes:
: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) writes:
: >In general, use of index variables (such as $i) is a warning sign that
: >there's a better way to do it in Perl.
: 
: Really? Please enlighten me....
: 
: I want to process an array of stuff @stuff. Lets say that I want to 
: do a "tolower" on each element of stuff (an array of text strings).
: 
: The current way I do this is (yes I am a C programmer to the core):
:                                         
: for($i=0; $i<$#stuff; $i++) {
: 	$stuff[$i] =~ tr/A-Z/a-z/;
: }
: 
: Is there a better way?

Yes.  There are some iterators that cause the loop variable to refer to
each array element directly, much like a C programmer would use a pointer to
iterate through an array, only without having to dereference anything.
You can simply say

    foreach $elem (@stuff) {
	$elem =~ tr/A-Z/a-z/;
    }

or, more briefly,

    for (@stuff) {	# equivalent to "foreach $_ (@stuff)"
	tr/A-Z/a-z/;
    }

or even more briefly,

    grep(tr/A-Z/a-z/, @stuff);

The other place that index variables pop up unnecessarily is when people
write linear searches down a numerically indexed array, when they should be
using associative arrays to do a direct lookup, or using one of the other
built-in searching mechanisms.

Larry