Getting Started with PHP: PHP and the Shell

PHP Getting Started Guide: PHP and Shell

With the development of the Internet, the PHP language has gradually become one of the most popular server-side scripting languages ​​​​in the open source community. It combines the characteristics of programming languages ​​such as C, Java and Perl, and is simple, efficient and easy to learn. It is widely used in website development, application, mobile application development and other fields. In this article, we will introduce the basic structure, syntax and common functions of PHP programs by explaining the relationship between PHP and Shell, helping PHP beginners quickly master this language.

1. The basic structure of the PHP program

The basic structure of the PHP program consists of a start tag , with a PHP code block in the middle. For example, the following is a simple PHP program:

<?php
echo "Hello World!";
?>

In this code, echo is a PHP output function used to output strings to the browser. In PHP, all code must be between the opening tag and the closing tag.

2. PHP variables and data types

A PHP variable is a value or a reference that can be used multiple times in the program. In PHP, variables start with $ sign. For example:

<?php
$name = "Jack";
$age = 30;
?>

PHP supports multiple data types, including strings, integers, floating point numbers, Boolean values, arrays, objects, and NULL values. For example:

<?php
$string = "Hello world!";
$integer = 123;
$float = 3.14159;
$boolean = true;
$array = array("apple", "orange", "banana");
$object = new stdClass();
$null = null;
?>

3. PHP operators and control structures

PHP supports a variety of operators, including arithmetic operators, comparison operators, logical operators, etc. For example:

<?php
$a = 10;
$b = 20;
$c = $a + $b; // 加法
$d = $a - $b; // 减法
$e = $a * $b; // 乘法
$f = $a / $b; // 除法
$g = $a % $b; // 取模
$h = $a == $b; // 等于
$i = $a != $b; // 不等于
$j = $a > $b; // 大于
$k = $a < $b; // 小于
$l = $a >= $b; // 大于或等于
$m = $a <= $b; // 小于或等于
$n = !($a && $b); // 逻辑非
$o = ($a || $b); // 逻辑或
$p = ($a && $b); // 逻辑与
?>

PHP also supports a variety of control structures, including if, else, for, while, do-while, switch, etc. For example:

<?php
$score = 80;
if ($score >= 90) {
    echo "Excellent";
} elseif ($score >= 80) {
    echo "Good";
} elseif ($score >= 70) {
    echo "Fair";
} else {
    echo "Fail";
}

for ($i = 0; $i < 10; $i++) {
    echo $i;
}

$x = 0;
while ($x < 10) {
    echo $x;
    $x++;
}

$y = 0;
do {
    echo $y;
    $y++;
} while ($y < 10);

$fruit = "apple";
switch ($fruit) {
    case "apple":
        echo "It's an apple";
        break;
    case "orange":
        echo "It's an orange";
        break;
    default:
        echo "Unknown fruit";
}
?>

4. PHP functions

PHP has a large number of built-in functions, which can greatly simplify the writing of program code. PHP functions can be built-in functions or user-defined functions. For example:

<?php
// 内置函数
echo strlen("Hello world!"); // 输出 12

// 自定义函数
function add($a, $b) {
    return $a + $b;
}
echo add(1, 2); // 输出 3
?>

5. PHP and Shell

Shell is a command line interpreter that can interact with the inside of the operating system. This tool is pre-installed in most UNIX systems. Shell is a scripting language that can run system commands and perform some basic arithmetic operations, and can modify the operating system environment through some predefined variables.

PHP and Shell can be used together. By using PHP's exec function, you can execute the Shell script in the PHP program and get the return value of the Shell script. For example:

<?php
// 执行 Shell 脚本
$output = array();
exec("ls -la", $output, $return_var);

// 输出 Shell 脚本的输出和返回值
echo implode("
", $output) . "
";
echo "Return value: " . $return_var . "
";
?>

6. Conclusion

This article introduces the basic structure, variables and data types, operators and control structures, functions and Shell of PHP programs. After learning these basic knowledge, PHP beginners can better understand and use PHP and write efficient program codes faster.

In the process of learning PHP, it is recommended to write more simple programs and read PHP's official documentation to gain more practical experience. Through continuous learning and practice, I believe you can also become an excellent PHP programmer!

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