What is difference between PHP cli and PHP cgi?

Solution 1:

From http://www.php-cli.com/php-cli-cgi.shtml

These are the most important differences between CLI and CGI:

• Unlike the CGI SAPI, CLI writes no headers to the output by default
• There are some php.ini directives which are overridden by the CLI SAPI because they do not make sense in shell environments:
  • html_errors: CLI default is FALSE
  • implicit_flush: CLI default is TRUE
  • max_execution_time: CLI default is 0 (unlimited)
  • register_argc_argv: CLI default is TRUE
• You can have command line arguments with your script! Variable "$argc" provides you with a number of arguments passed to the application. And array "$argv" gives you an array of the actual arguments
• There are 3 new constant defined for the shell environment: STDIN, STDOUT, STDERR. All of them are file handlers for correspondent shell devices. For example STDIN is the handler for fopen('php://stdin', 'r') . So, you can read a line from STDIN like this: $strLine = trim(fgets(STDIN));. STDIN is already defined for you by PHP CLI!
• PHP CLI does not change the current directory to the directory of the executed script. The current directory for the script would be the directory where your type PHP CLI command.
• There are number of USEFUL options available for PHP CLI. Which will allow you to get some valuable information about you php setup, your php script or run it in different modes.
• In PHP 5 there were some changes in CLI and CGI filenames. In PHP 5, the CGI version was renamed to php-cgi.exe (previously php.exe) and the CLI version now sits in the main directory (previously cli/php.exe).
• In PHP 5 it was also introduced a new mode: php-win.exe. This is equal to the CLI version, except that php-win doesn't output anything and thus provides no console (no "dos box" appears on the screen). This behaviour is similar to PHP GTK.

Solution 2:

This might give you a broader understanding of their difference:

CGI: (common gateway interface) It is a specification "protocol" for transferring information between a Web server and a CGI program.

A CGI program is any program designed to accept and return data that conforms to the CGI specification.

Basically it's a way to run a server side script (PHP, Perl, Python,...) when a HTTP request comes.

CGI is very slow in comparison to other alternatives.

FastCGI: is a better CGI.

Fast CGI is a different approach with much faster results.

It is a CGI with only a few extensions.

FastCGI implementation isn’t available anymore, in favor of the PHP-FPM.

PHP-FPM: (FastCGI Process Manager), it's a better FastCGI implementation than the old FastCGI.

It runs as a standalone FastCGI server.

In general it's a PHP interface for the web servers (Apache, Nginx..) to allows Web Server to interact with PHP.

Unlike the PHP-CLI which is a command line interface for PHP to allows Users to interact with PHP via terminal.

mod_php: an Apache module to run PHP.

It execute PHP scripts inside the Web Server directly as part of the web server without communicating with a CGI program.

mod_SuPHP: is similar to mod_php but can change the user/group that the process runs under.

Basically it address some problems of mod_php related to permissions.