php教程，echo语句中双引号单引号及其它输出变量的方式

echo "hello world";

$hello = "hola";
$world = "苏南大叔";

echo $hello." ".$world;
echo $hello.' '.$world;
echo $hello.` `.$world;  // 注意这个输出没有空格

hola 苏南大叔
hola 苏南大叔
hola苏南大叔

echo $hello," ",$world;
echo $hello,' ',$world;
echo $hello,` `,$world;  // 注意这个输出没有空格

hola 苏南大叔
hola 苏南大叔
hola苏南大叔

echo "$hello,$world";
echo "{$hello}{$world}";
echo "$hello$world";
echo "$hello$world呀";   // 错误

hola,苏南大叔
hola苏南大叔
hola苏南大叔
hola

echo '$hello,$world';      // 错误
echo '{$hello}{$world}';   // 错误
echo '$hello$world';       // 错误
echo $hello.' '.$world;
echo $hello,' ',$world;
echo $hello,' ',$world,"\r\n";
echo $hello,' ',$world,'\r\n';

$hello,$world
{$hello}{$world}
$hello$world
hola 苏南大叔
hola 苏南大叔
hola 苏南大叔
hola 苏南大叔\r\n

echo "1\r\n";
echo `$hello,$world`;      // 错误
echo "\r\n2\r\n";
echo `{$hello}{$world}`;   // 错误
echo "\r\n3\r\n";
echo `$hello$world`;       // 错误
echo "\r\n4\r\n";
echo $hello.` `.$world;
echo "\r\n5\r\n";
echo $hello,` `,$world;

1

2

3

4
hola苏南大叔
5
hola苏南大叔

$command = "chdir";
echo $command;
echo `${command}`;
echo `$command`;

chdir
C:\Users\sunan\Desktop\test\php
C:\Users\sunan\Desktop\test\php

$str = <<<EOF
$hello,$world \r
$hello,$world呀！\r
{$hello},{$world}呀！\r
EOF;
echo $str;

hola,苏南大叔 
hola,
hola,苏南大叔呀！

echo "hello world",PHP_EOL;
echo "hello world","\r\n";