regexp - character class containing zero does not find zero

princepawn has asked for the wisdom of the Perl Monks concerning the following question:

For the following code:

my $test = shift;  # we want a binary "tape" of 1s and 0s as the arg

unless ( $test and $test =~ /^[01]+$/ ) {
    die "Your input was: $test\nGive a string (tape) of zeros and ones
+ only!\n";
}
my @test_queue = split '', $test; # turn string into queue/array
[download]

We get the following behavior even though a single zero should pass the regexp test. A single one does pass, BTW.

Anyone know why? Gracias.

c:\Documents and Settings\1\My Documents\perl\dfa\simple>code.pl 0
code.pl 0
Your input was: 0
Give a string (tape) of zeros and ones only!
[download]

Comment on regexp - character class containing zero does not find zero Select or Download Code

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Re: regexp - character class containing zero does not find zero by diotalevi (Canon) on Sep 27, 2002 at 05:43 UTC
The value '0' evaluates to false in a boolean context so your `and` test fails. Why not use defined() or m/^./ to test for the presence of a $test value?	[reply] [d/l]
Re: regexp - character class containing zero does not find zero by tadman (Prior) on Sep 27, 2002 at 06:05 UTC
There's a few responses about why it's failing. Here's an idea on how to repair it: `my ($test) = @ARGV; unless (defined($test) && test =~ /^[01]+$/) { die "..."; } my @test_queue = split('', $test);` [download]	[reply] [d/l]
Re: regexp - character class containing zero does not find zero by Zaxo (Archbishop) on Sep 27, 2002 at 05:45 UTC
`unless ( $test and $test =~ /^[01]+$/ ) { ...` never gets to the regex since $test is false. After Compline, Zaxo	[reply] [d/l]