[Chicago-talk] Two Perl curiosities

Alan Mead amead2 at alanmead.org
Tue May 19 11:02:27 PDT 2015

I have two odd Perl things I've noticed recently. I'm using the stock
Centos 6.6 perl (v5.10.1 + whatever black magic Red Hat added).

Curiosity #1: I can't post the entire program code but I have a long script:


use strict;
use warnings;

[... about 150 lines omitted, including the beginning of a loop in a

          my $a = $$pars{'alpha'};
          my $delta = $$pars{'delta'};
          my $taus = $$pars{'taus'};
          print $fh join("\t", ($a, >>$b<<, 0, @$taus)), "\n"  # >> <<
is my emphasis

I meant to type "delta" but I typed "b".  Shouldn't Perl throw an error
because of the strict pragma or at least a warning? I get no warnings
when I "perl -c" and when running, all the warning I get is that $b is
uninitialized.  When I create a small test script with this kind of
error, I get a warning: "Name "main::b" used only once: possible typo at
./test.pl line 11."

Curiosity #2: Also, I converted a program from Pascal to Perl and I
forgot one assignment operator (e.g., something like my $a := 1;) and
Perl never complained.  What does := do in Perl? It's hard to google
ops. In a test program, it looks like it's a valid assignment operator?

$ cat test.pl
use strict;
use warnings;
my $a := 42;
print "$a\n";
$ ./test.pl



Alan D. Mead, Ph.D.
President, Talent Algorithms Inc.

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