Input/output streams

The CLI SAPI defines a few constants for I/O streams to make programming for the command line a bit easier.

**CLI 专用常量**
常量名称	描述
`STDIN`	An already opened stream to `stdin`. This saves opening it with `<?php $stdin = fopen('php://stdin', 'r'); ?>` If you want to read single line from `stdin`, you can use `<?php $line = trim(fgets(STDIN)); // reads one line from STDIN fscanf(STDIN, "%d\n", $number); // reads number from STDIN ?>`
`STDOUT`	An already opened stream to `stdout`. This saves opening it with `<?php $stdout = fopen('php://stdout', 'w'); ?>`
`STDERR`	An already opened stream to `stderr`. This saves opening it with `<?php $stderr = fopen('php://stderr', 'w'); ?>`

有了以上常量，就无需自己建立指向诸如 stderr 的流，只需简单的使用这些常量来代替流指向：

php -r 'fwrite(STDERR, "stderr\n");'

无需自己来关闭这些流，PHP 会在脚本结束时自动完成这些操作。

注意:
These constants are not available if reading the PHP script from stdin.