PHP echo output string function details

echo "asd";//string
echo "ads$c";//String + variable
echo 'ads$c';//stringasd$c $c Is not a variable  
echo "sd"."vs"; 
echo "sd","vs"; 
echo $a; 
echo $a.$b; 
echo $a,$b; 
echo $a.$b.$c; 
echo $a,$b,$c; 
echo "kaskd{$c}asd"; 
echo "kakskd{$arr['lo']}"; 
echo "kakskd{$obj->a}"; 
echo "kaskd".$c."kasd"; 
echo "kaskd".$arr['lo']."kasd"; 
echo "kaskd".$obj->a."kasd"; 
echo "kaskd".func($c)."kasd"; 
echo "kaksk".($a+1)."dkkasd"; 
echo $c."jaksd"; 
echo $c,"jaksd"; 
//PHP multiline output method
echo <<<END 
This uses the "here document" syntax to output 
END; 
//Output short
<?php echo $a;?> 　　<?=$a?> 

<?php 
echo "Hello World"; 

echo "This spans 
multiple lines. The newlines will be 
output as well"; 

echo "This spansnmultiple lines. The newlines will benoutput 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 
$baz = array("value" => "foo"); 

echo "this is {$baz['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 
?> 

Here is the official manual:
The Definition and the Usage
Definition and usage
The echo() function output one or more strings.
The echo() function outputs one or more strings.
Syntax
grammar
Echo (strings)
The Parameter Parameter Description
One or more strings to be sent to the output
Required parameters. Specifies one or more strings that need to be sent to the result
Tips and Notes
Tips and attention points
Note: The echo () function is not later a function, so you are not required to use parentheses with it. Or, if you want to pass more than one parameter to echo (), Using parentheses will generate a parse error.
Note: the echo() function is not really a function, so you don't have to use it. If you want to pass more than one argument to the echo() function, using the parenthesis "()" will cause an error.
The echo() function is slightly faster than print().
Tip: the echo() function is equivalent to a simplified version of the print() function.
Tip: The echo() function has The following shortcut. See example 5.
Tip: the echo() function contains the following shorthand. See case 5 for details.
Example 1
Case 1

 
<?php 
$str = "Who's Kai Jim?"; 
echo $str; 
echo "<br />"; 
echo $str."<br />I don't know!"; 
?> 

The output of The code above will be:
The above code will output the following results:
Who 's Kai, Jim? Who 's Kai, Jim? I don 't know!

Example 2
Case 2

 
<?php 
echo "This textspans multiplelines."; 
?> 

The output of The code above will be:
The above code will output the following results:
This text spans multiple lines.

Example 3
Case 3

 
<?php 
echo 'This ','string ','was ','made ','with multiple parameters'; 
?> 

The output of The code above will be:
The above code will output the following results:
This string was made with multiple parameters

Example 4
Case 4
Difference of single and double quotes. Single quotes will print the variable name, not the value:
Distinguish between single (') and double (") quotation marks. Single quotes will output the variable name, not the value of the variable:

 
<?php 
$color = "red"; 
echo "Roses are $color"; 
echo "<br />"; 
echo 'Roses are $color'; 
?> 

The output of The code above will be:
The above code will output the following results:
Roses are redRoses are $color

Example 5
Case 5
Shortcut syntax:
Shorthand (shortcut) grammar:

 
<html><body> 
<?php 
$color = "red"; 
?><p>Roses are <?=$color?></p></body></html>