Perl regexp 如何仅转义某些字符

使用 Perl 正则表达式仅转义某些字符

perl
my $string = "Hello.world";
if ($string =~ /Hello\.world/) {
    print "Matched!";
}

perl
my $string = "apple|orange";
if ($string =~ /apple\|orange/) {
    print "Matched!";
}

perl
my $string = "";
if ($string =~ /\/) {
    print "Matched!";
}

perl
my $string = "http://www.example.com";
if ($string =~ /http:\/\/www\.example\.com/) {
    print "Matched!";
}

perl
my $string = "Hello.world";
if ($string =~ /Hello[.]world/) {
    print "Matched!";
}