perl-basic-分支&循环

• if

1. elsif
2. shorter if: if+condition放在句子尾部。

use strict;
use warnings;

my $word = "antidisestablishmentarianism";
# get the length of a scalar
my $strlen = length $word;

if($strlen >= 15) {
	print "'", $word, "' is a very long word";
# elsif
} elsif(10 <= $strlen && $strlen < 15) {
	print "'", $word, "' is a medium-length word";
} else {
	print "'", $word, "' is a short word";
}
# short form of IF
print "'", $word, "' is actually enormous" if $strlen >= 20;

• unless...if

my $temperature = 10;

unless($temperature > 30) {
# condition is false
	print $temperature, " degrees Celsius is not very hot";
} else {
# condition is true
	print $temperature, " degrees Celsius is actually pretty hot";
}
# condition is false, then print
print "Oh no it's too cold" unless $temperature > 15;

• 允许使用三元运算符?:且可以嵌套：

my $eggs = 5;
print "You have ", $eggs == 0 ? "no eggs" :
                   $eggs == 1 ? "an egg"  :
                   "some eggs";

　

---

• while()，until(), do...while，do...until和for类似c
• 循环一个数组时不必用for循环。。用foreach

my @arr = ("hi", "my", "lady");
foreach my $str (@arr) {
    print $str;
    print "\n";
    }　　

或者极简形式：

print $_ foreach @arr;

如果需要索引值，用这个：

foreach my $i ( 0 .. $#arr ) {
	print $i, ": ", $arr[$i];
}

• 循环hash时：因为用keys返回hash的key是无序的，所以先用sort排序。

foreach my $key (sort keys %scientists) {
	print $key, ": ", $scientists{$key};
}

• 循环控制：next = continue, last = break, 可以从循环中跳转到label处，label必须全大写

CANDIDATE: for my $candidate ( 2 .. 100 ) {
	for my $divisor ( 2 .. sqrt $candidate ) {
		next CANDIDATE if $candidate % $divisor == 0;
	}
	print $candidate." is prime\n";
}