为什么比较运算符==不适用于perl中的字符串？

Question

I'm new to Perl. I want to understand why does == operator is treating both these strings alike? It works ok if I use eq instead if ==. If name is kuldeep or rahul, it prints 'Right name'.

my $name="kuldeep";

if ($name == "rahul")
{
  print 'Right name!',"\n";
}
else
{
  print 'Wrong name!','\n';
}

Answer 1

You are mistaken. The numerical equality comparison operator works perfectly fine with strings!

$ perl -e'CORE::say "123" == "123.0" ? "same" : "different"'
same

$ perl -e'CORE::say "123" == "123.1" ? "same" : "different"'
different

In your example, you are asking Perl to compare the numerical value of the string kuldeep (zero with a warning) with the numerical value of the string rahul (zero with a warning), and they are indeed equal.

ALWAYS USE use strict; use warnings; use strict; use warnings; !!!

And use eq to compare strings.

Answer 2

Interpreter realizes (from the == operator) that it's doing a numeric comparison. The value of $name is converted to a numeric, which gets you a 0. "rahul" is converted to a numeric, which is a 0. 0 == 0, so that's true, and thus "Right name" is chosen.

If I compare it against my name, works the same way.

However, if there really is a string with a number in it, like you made either string "12345" (specifically with the quotes), Perl will assume you knew what you were doing by requesting the == operator, and will dutifully auto-convert ("cast" in programmer-speak) that to numeric 12345. Then your comparison will fail.

TL/DR: use 'eq' for string comparison! :-)