I've just been using this code to check if a string is empty:
if ($str == "")
{
// ...
}
And also the same with the not equals operator...
if ($str != "")
{
// ...
}
This seems to work (I think), but I'm not sure it's the correct way, or if there are any unforeseen drawbacks. Something just doesn't feel right about it.
转载于:https://stackoverflow.com/questions/2045644/what-is-the-proper-way-to-check-if-a-string-is-empty-in-perl
For string comparisons in Perl, use eq or ne:
if ($str eq "")
{
// ...
}
The == and != operators are numeric comparison operators. They will attempt to convert both operands to integers before comparing them.
See the perlop man page for more information.
The very concept of a "proper" way to do anything, apart from using CPAN, is non existent in Perl.
Anyways those are numeric operators, you should use
if($foo eq "")
or
if(length($foo) == 0)
You probably want to use "eq" instead of "==". If you worry about some edge cases you may also want to check for undefined:
if (not defined $str) {
# this variable is undefined
}
As already mentioned by several people, eq is the right operator here.
If you use warnings; in your script, you'll get warnings about this (and many other useful things); I'd recommend use strict; as well.
Due to the way that strings are stored in Perl, getting the length of a string is optimized.if (length $str) is a good way of checking that a string is non-empty.
If you're in a situation where you haven't already guarded against undef, then the catch-all for "non-empty" that won't warn is if (defined $str and length $str).
To check for an empty string you could also do something as follows
if (!defined $val || $val eq '')
{
# empty
}