regex - 正则表达式锚定到包含单词 "hello"的任何行的开头，以便它们在字符串中出现

Question

应该首先找到 hello，打印字符位置...找到下一个 hello 并打印字符位置... anchor 可以是具有第一个 你好...

为什么它不起作用？

尝试 #1:

$line = "\n hi\n   hiya \n   hello\n hi \n hello2";
$match = $line =~ m/^\s*(hello)/;
if (!$match) {
    die("not found\n");
}

print "found at pos: " . pos($line) . "\n";
$line = $';
$match = $line =~ m/^\s*(hello)/;
if (!$match) {
    die("not found\n");
}
print "found at pos: " . pos($line) . "\n";

结果:未找到

尝试#2:

$line = "\n hi\n   hiya \n   hello\n hi \n hello2";
$match = $line =~ m/\A\s*(hello)/;
if (!$match) {
    die("not found\n");
}

$line = $';
$match = $line =~ m/\A\s*(hello)/;
if (!$match) {
    die("not found\n");
}
print "found at pos: " . pos($line) . "\n";

结果:未找到

Answer 1

对于“多行”字符串需要/m modifier ^ 匹配字符串中的行开头

use warnings;
use strict;
use feature 'say';

my $line = "\n hi\n   hiya \n   hello\n hi \n hello2";


while ( $line =~ /^\s*(hello)/mg ) { 
    say $1; 
    say pos $line 
}

打印

hello
22
hello
34