Let's speculate on a context that might help make sense of this snippet:
#!/usr/bin/perl -w
use strict;
# List all non-common words in a block of text
my %stopwords = (a => 1, an => 1, in => 1, the => 1);
my %D2;
while ( <DATA> ) {
@D2{ map { my $l = lc;
exists $stopwords{$l} ? () : $l
} split /\W+/
} = ();
}
print "$_\n" for sort keys %D2;
__DATA__
This is a demo of an
interesting example
in the post
from PerlMonks.
Prints:
demo
example
from
interesting
is
of
perlmonks
post
this
In answer to your specific question,
exists $stopwords{$l}?():$l
uses the ? : trinary operator to say: If $l exists in the %stopwords hash return nothing (specifically, a null list), otherwise return $l itself. (Note that it is dollar-el, not dollar-one.)
Considering my imagined context for this snippet, we have a list of common (uninteresting) words commonly called stopwords. These we want to ignore. So we read through the file (I used the DATA filehandle) a line at a time. For each line we split out the words, force each one to lowercase, drop the stopwords, and then use the others to specify a hash slice on the hash called %D2. Every key in that slice (whether new or pre-existing at that point) is set to an empty value (I'm skipping over some nuances here). When we have finished with all the data, the %D2 hash contains an entry for every "interesting" word in the data set (ignoring duplicates).
Update: Trying to stay focused on the stated problem, I avoided the issue of the variable name $l (dollar-ell). Nkuvu is correct to point this out.
I would also add that this code will return odd results for text containing words with apostrophes or hyphens: "isn't" and "good-by" will be reported as: "isn", "t", "good", "by".
So this code is not recommended for Real Text in a situation where accuracy of results matters.
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"Perl is a mess
and that's good because the
problem space is also a mess." - Larry Wall
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