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
ConstantDescription
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 if reading the PHP script from stdin.