echo

Description

void echo ( string arg1 [, string ...] )

Outputs all parameters.

echo() is not actually a function (it is a language construct), so you are not required to use parentheses with it. echo() (unlike some other language constructs) does not behave like a function, so it cannot always be used in the context of a function. Additionally, if you want to pass more than one parameter to echo(), the parameters must not be enclosed within parentheses.

例子 1. echo() examples
<?php echo "Hello World"; echo "This spans multiple lines. The newlines will be output as well"; echo "This spans\nmultiple lines. The newlines will be\noutput as well."; echo "Escaping characters is done \"Like this\"."; // You can use variables inside of an echo statement $foo = "foobar"; $bar = "barbaz"; echo "foo is $foo"; // foo is foobar // You can also use arrays $bar = array("value" => "foo"); echo "this is {$bar['value']} !"; // this is foo ! // Using single quotes will print the variable name, not the value echo 'foo is $foo'; // foo is $foo // If you are not using any other characters, you can just echo variables echo $foo; // foobar echo $foo,$bar; // foobarbarbaz // Some people prefer passing multiple parameters to echo over concatenation. echo 'This ', 'string ', 'was ', 'made ', 'with multiple parameters.', chr(10); echo 'This ' . 'string ' . 'was ' . 'made ' . 'with concatenation.' . "\n"; echo <<<END This uses the "here document" syntax to output multiple lines with $variable interpolation. Note that the here document terminator must appear on a line with just a semicolon. no extra whitespace! END; // Because echo does not behave like a function, the following code is invalid. ($some_var) ? echo 'true' : echo 'false'; // However, the following examples will work: ($some_var) ? print 'true' : print 'false'; // print is also a construct, but // it behaves like a function, so // it may be used in this context. echo $some_var ? 'true': 'false'; // changing the statement around ?>

echo() also has a shortcut syntax, where you can immediately follow the opening tag with an equals sign. This short syntax only works with the short_open_tag configuration setting enabled.


I have <?=$foo?> foo.

For a short discussion about the differences between print() and echo(), see this FAQTs Knowledge Base Article: http://www.faqts.com/knowledge_base/view.phtml/aid/1/fid/40

注: 由于这是一个语言结构而非函数，因此它无法被变量函数调用。

See also print(), printf(), and flush().

add a note User Contributed Notes

rwruck
28-Jan-2006 05:15


It should be mentioned here that the script will be aborted if you output something in response to a HTTP HEAD request.

In the following example, the second line will NOT be written to the file. Any registered shutdown function will be called, though:



<?php

$hf = fopen('head.log', 'ab');

fwrite($hf, "before output\n");

echo "Test";

fwrite($hf, "after output\n");

fclose($hf);

?>



This is normal behaviour; see the description of $_SERVER.

lorenpr at gmail dot com
15-Sep-2005 12:12


I hope this ternary thing isn't overkill. Last thing - I would just like to make you aware of the side effect when you do this statement, 

 

echo $some_var ? print 'true': print 'false';



The result would be either 'true1' or 'false1', depending on whether $some_var is true or false respectively. This happens because of what I mentioned earlier. Figure it out.

lorenpr at gmail dot com
15-Sep-2005 11:58


linus is correct.

The ternary relationship is evaluated first, then echo prints the result.



Also, keep in mind

(condition? a : b) 

reads 

if(condition) return a; else return b;



So what makes 

A. echo ($somevar) ? 'true' : 'false';



different from



B. ($somevar) ? echo 'true' : echo 'false';



is the ternary relationship in A reads

if (condition) return 'true'; else return 'false';



while in B it reads

if(condition) return (echo 'true'); else return (echo 'false');



- an invalid statement, since echo evaluates to void.

linus.martensson a gmail
25-Aug-2005 05:03


Simple. it reads like echo (($somevar)?'true';'false'); and outputs the result, unless I'm mistaken.

shannonmoeller at gmail dot com
10-Aug-2005 07:31


In reply to lorenpr at gmail dot com:



If what you say is true, why does this work?



<?php

echo ($somevar) ? 'true' : 'false'; //works

?>

lorenpr at gmail dot com
29-Jul-2005 01:17


I just want to point out something to beginners. The documentation is misleading where it says:



// Because echo is not a function, following code is invalid.

($some_var) ? echo 'true' : echo 'false';



The code is invalid, but not because 'echo' is a language construct, but rather because 'echo' does not return a value. 

So don't be mislead: the syntax used above is certainly not limited to functions.



You must keep in mind that the job of the ternary syntax used is not actually to display anything, but to test a boolean relationship. The 'print' statement would work because it always returns a 1, which in php, is interpreted to a boolean  'true'. Things that return 'void' cannot be expected to evaluate to a 'true' or 'false', and that is why using 'echo' in this particular case is invalid.

Jason Carlson - SiteSanity
17-May-2005 01:28


In response to Ryan's post with his echobig() function, using str_split wastes memory resources for what you are doing. 



If all you want to do is echo smaller chunks of a large string, I found the following code to perform better and it will work in PHP versions 3+



<?php

function echobig($string, $bufferSize = 8192)

{

  // suggest doing a test for Integer & positive bufferSize

  for ($chars=strlen($string)-1,$start=0;$start <= $chars;$start += $bufferSize) {

    echo substr($string,$start,$buffer_size);

  }

}

?>

renrutal at gmail dot com
29-Mar-2005 07:34


Note that:



<?php

echo "2 + 2 = " . 2+2; // This will print 4

echo "2 + 2 = " , 2+2; // This will print 2+2 = 4

?>



The commas will parse the result of the expressions correctly.

ryan at wonko dot com
27-Feb-2005 04:56


Due to the way TCP/IP packets are buffered, using echo to send large strings to the client may cause a severe performance hit. Sometimes it can add as much as an entire second to the processing time of the script. This even happens when output buffering is used.



If you need to echo a large string, break it into smaller chunks first and then echo each chunk. The following function will do the trick in PHP5:



<?php

function echobig($string, $bufferSize = 8192)

{

    $splitString = str_split($string, $bufferSize);



    foreach($splitString as $chunk)

        echo $chunk;

}

?>

Truffy
15-Jan-2005 05:02


You can use braces around variables as well as array items. This is useful to help recognition of your variables in your code, but most useful where the variable iteslf cannot be separated with spaces from the preceding/following code, for exmple in a file path:



If a path is assigned the variable $path, then this code will not work:



echo "$pathindex.php";



whereas this will



echo "{$path}index.php";

zombie)at(localm)dot(org)
26-Jan-2003 03:26


[Ed. Note: During normal execution, the buffer (where echo's arguments go) is not flushed (sent) after each write to the buffer. To do that you'd need to use the flush() function, and even that may not cause the data to be sent, depending on your web server.]





Echo is an i/o process and i/o processes are typically time consuming. For the longest time i have been outputting content by echoing as i get the data to output. Therefore i might have hundreds of echoes in my document. Recently, i have switched to concatenating all my string output together and then just doing one echo at the end. This organizes the code more, and i do believe cuts down on a bit of time. Likewise, i benchmark all my pages and echo seems to influence this as well. At the top of the page i get the micro time, and at the end i figure out how long the page took to process. With the old method of "echo as you go" the processing time seemed to be dependent on the user's net connection as well as the servers processing speed. This was probably due to how echo works and the sending of packets of info back and forth to the user. One an one script i was getting .0004 secs on a cable modem, and a friend of mine in on dialup was getting .2 secs. Finally, to test that echo is slow; I built strings of XML and XSLT and used the PHP sablotron functions to do a transformation and return a new string. I then echoed the string. Before the echo, the process time was around .025 seconds and .4 after the echo. So if you are big into getting the actual processing time of your scripts, don't include echoes since they seem to be user dependent. Note that this is just my experience and it could be a fluke.

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