perl中的“<<”，“ - ”和php中的实现是什么意思？

Question

I am converting some Perl code to PHP.
However, I do not know much about Perl, so I have to code it with a rough meaning.

And, I do not understand what the below Perl code means...

What is the meaning of $req2->content(<<"POST_DATA") and --$boundary?
I've searched the Perl documentation, but it's too hard to find.

PHP code:

...
$boundary= 'Nobody-has-the-intention-to-erect-a-wall'; 

$req2 = curl_init($search_url); 
curl_setopt($req2, CURLOPT_SSL_VERIFYPEER, 0); 
curl_setopt($req2, CURLOPT_CUSTOMREQUEST, "POST"); 
curl_setopt($req2, CURLOPT_POSTFIELDS, $data_string); 
curl_setopt($req2, CURLOPT_RETURNTRANSFER, true); 
curl_setopt($req2, CURLOPT_COOKIE, $cookie); 
curl_setopt($req2, CURLOPT_HTTPHEADER, array( 
'Content-Type: multipart/form-data;boundary='.$boundary, 
'Content-Length: ' . strlen($data_string)) 
); 
$result= curl_exec($req2); 
...

Perl code:

...
my $boundary= 'Nobody-has-the-intention-to-erect-a-wall';
$req2->content_type('multipart/form-data;boundary='.$boundary);
$req2->header("Cookie"=>"access_token_cookie=$access_token_cookie; csrf_access_token=$csrf_access_token");

$req2->content(<<"POST_DATA"); #what means this?

--$boundary
Content-Disposition: form-data; name="num_result"
Content-Type: text/plain

$num_result
--$boundary
Content-Disposition: form-data; name="img"; filename="search.jpg"
Content-Type: image/jpeg

$image
--$boundary--
POST_DATA

my $res = $ua->request($req2);
...

Answer 1

Nothing very different from PHP actually.

• << Heredoc, also present in PHP with slight differences:

  echo (<<<"POST_DATA"
  First line
  Second line
  POST_DATA
  );
  

• -- Variable decrease, as in <?php $a=2; echo --$a;

Note:

Of course, inside a Heredoc -- is just text.

---

Suggestion:

If you don't fully understand the Perl, try to run it (it's not evil code).

my $boundary = 'Nobody-has-the-intention-to-erect-a-wall';
print(<<"POST_DATA");

--$boundary
Content-Disposition: form-data; name="num_result"
Content-Type: text/plain

$num_result
--$boundary
Content-Disposition: form-data; name="img"; filename="search.jpg"
Content-Type: image/jpeg

$image
--$boundary--
POST_DATA

Will yield:

 
--Nobody-has-the-intention-to-erect-a-wall
Content-Disposition: form-data; name="num_result"
Content-Type: text/plain


--Nobody-has-the-intention-to-erect-a-wall
Content-Disposition: form-data; name="img"; filename="search.jpg"
Content-Type: image/jpeg


--Nobody-has-the-intention-to-erect-a-wall--