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PHP provides many predefined constant functions: PHP_VERSION returns the PHP version. PHP_OS returns the current operating system name. PHP_SAPI returns the server API that PHP runs under. PHP_EOL returns the system newline character. E_ALL returns an integer containing all error levels.
Commonly used predefined constant functions in PHP
PHP provides a large number of predefined constant functions. Help us get information about the current PHP environment and scripts. The following are some of the commonly used functions:
1. PHP_VERSION
Returns the version number of PHP, such as "7.4.25" or "8.1.6".
2. PHP_OS
Returns the name of the current operating system, such as "Linux", "Windows" or "macOS".
3. PHP_SAPI
Returns the server API used by the current PHP run, such as "cli" (command line interface), "apache2handler" (Apache module) or " cgi-fcgi" (CGI/FastCGI).
4. PHP_EOL
Returns the string containing the newline character in the current system, such as "\n" (Unix) or "\r\n" (Windows).
5. E_ALL
Returns an integer containing all error levels, such as 2047.
6. E_ERROR
Returns an integer indicating the error level E_ERROR, for example 1.
7. E_WARNING
Returns an integer indicating the error level E_WARNING, for example 2.
8. E_NOTICE
Returns an integer indicating the error level E_NOTICE, for example 8.
9. E_USER_ERROR
Returns an integer indicating the error level E_USER_ERROR, for example 256.
10. E_USER_WARNING
Returns an integer indicating the error level E_USER_WARNING, for example 512.
11. E_USER_NOTICE
Returns an integer representing the error level E_USER_NOTICE, such as 1024.
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