Why does "bob" == "godzilla" in Perl? - perl

Question

In Perl class today, a student turned in an assignment which vexes me. We are studying ARGV, but the result was not what I expected. His program (meme.pl) was:
#!/usr/bin/perl
$A = $ARGV[0];
chomp($A);
if ($A == "godzilla"){
print "$A\n";
}
else {
print "We need a monster's name\n";
}
If I type:
% ./meme.pl bob
the result is
% bob
So the variable assignment works, and but the condition ($A == "godzilla") is true no matter what is typed on the command line. I expected that since $ARGV[0] is "bob" and $A=$ARGV[0], then it should not true that $A="godzilla."
What am I missing? I have combed through this code for hours, and I know I am just overlooking some small thing.

Answer 1

Use eq, not ==, to test string equality:
if ($A eq "godzilla"){
More information is available at perldoc perlop.
Note: Adding use strict; and use warnings; to the top of your script would have led you in the right direction.

Answer 2

use strict; and use warnings; should be on...instant F in my book.
But no...evaluations of strings using "==" evaluate all strings - except those that start with a number like '123bob' (see comment below) - as numerical 0. That is why it is evaluating to true - it's "turning into" the statement 0 == 0. use warnings; would have told you something was up.
As many have said - use eq for strings.
More evidence and options can be found here: (http://perlmeme.org/howtos/syntax/comparing_values.html)
The pertinent excerpt (example program):
#!/usr/bin/perl
use strict;
use warnings;
my $string1 = 'three';
my $string2 = 'five';
if ($string1 == $string2) {
print "Equal\n";
} else {
print "Not equal\n";
}
From the above example, you would get warning messages and both strings would evaluate to zero:
Argument "five" isn't numeric in numeric eq (==) at ./test.pl line 8.
Argument "three" isn't numeric in numeric eq (==) at ./test.pl line 8.
Equal
You aren't getting those warnings...just the "Equal", thanks to the absence of use warnings; at the top of your - errr...your student's...cough... - code. ;)

Answer 3

When you are comparing strings, you must use "eq" instead of "==". So replace
($A == "godzilla")
by
($A eq "godzilla")

Answer 4

What the others said is correct about using eq to compare strings. However, the test passes, because when compared numerically with == the string 'bob' and the string 'godzilla' both evaluate to 0, so the test passes and you get bob.