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

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