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 specific Constants

Constant	Description
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'); ?>

Given the above, you don't need to open e.g. a stream for stderr yourself but simply use the constant instead of the stream resource:

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

You do not need to explicitly close these streams, as they are closed automatically by PHP when your script ends.

Note:

These constants are not available in case of reading PHP script from stdin.