Perl 数字与字符串运算符之区别

在Perl中，字符串比较和数字比较是由不同的运算符来完成的：

• 数字比较运算符： <,>,<=,>=,==,!=
• 字符串比较运算符： lt,gt,le,ge,eq,ne
• cmp： 比较字符串，返回 -1,0 或者 1。
• <=>： 比较数字，返回 -1,0 或者 1。
• =~：用正则表达式来匹配，匹配的话返回True。
• !~：和 =~ 相反，不匹配返回True。

我有好几次都用错了，结果浪费了很多时间在调试上面。

#!/usr/bin/env perl
use strict;
use warnings;
 
my $num1 = 1;
my $num2 = 1.0;
my $two_numbers = "$num1 and $num2";
 
my $str1 = "1abc";
my $str2 = "1xyz";
my $two_strings = "$str1 and $str2";
 
print "Compare two numbers using !=\n";
if ($num1 != $num2) {
    print "$two_numbers are not equal\n";
} else {
    print "$two_numbers are equal\n";
}
 
print "Compare two strings using !=: get wrong result\n";
if ($str1 != $str2) {
    print "$two_strings are not equal\n";
} else {
    print "$two_strings are equal\n";
}
 
print "Compare two numbers using ne\n";
if ($num1 ne $num2) {
    print "$two_numbers are not equal\n";
} else {
    print "$two_numbers are equal\n";
}
 
print "Compare two strings using ne\n";
if ($str1 ne $str2) {
    print "$two_strings are not equal\n";
} else {
    print "$two_strings are equal\n";
}

Compare two numbers using !=
1 and 1 are equal
Compare two strings using !=: get wrong result
Argument "1xyz" isn't numeric in numeric ne (!=) at compare_operators.pl line 23.
Argument "1abc" isn't numeric in numeric ne (!=) at compare_operators.pl line 23.
1abc and 1xyz are equal
Compare two numbers using ne
1 and 1 are equal
Compare two strings using ne
1abc and 1xyz are not equal