PHP CLI vs. STDIN / STDOUT / STDERR — https://bugs.php.net/bug.php?id=43283

php-file.sh

$ echo "<?php var_dump(STDOUT);" > y.stdout
$ php y.stdout
resource(2) of type (stream)

php-opt.sh

$ php -r "var_dump(STDOUT);"
resource(2) of type (stream)

php-piped-stdin.sh

$ echo "<?php var_dump(STDOUT);" | php
PHP Notice:  Use of undefined constant STDOUT - assumed 'STDOUT' in - on line 1
PHP Stack trace:
PHP   1. {main}() -:0

Notice: Use of undefined constant STDOUT - assumed 'STDOUT' in - on line 1

Call Stack:
    0.0000     125824   1. {main}() -:0

string(6) "STDOUT"

php-redir-stdin.sh

$ echo "<?php var_dump(STDOUT);" > y.stdout
$ php < y.stdout
PHP Notice:  Use of undefined constant STDOUT - assumed 'STDOUT' in - on line 1
PHP Stack trace:
PHP   1. {main}() -:0

Notice: Use of undefined constant STDOUT - assumed 'STDOUT' in - on line 1

Call Stack:
    0.0000     125824   1. {main}() -:0

string(6) "STDOUT"

php-stdin.sh

$ php
<?php
var_dump(STDOUT);
^Z
PHP Notice:  Use of undefined constant STDOUT - assumed 'STDOUT' in - on line 2
PHP Stack trace:
PHP   1. {main}() -:0

Notice: Use of undefined constant STDOUT - assumed 'STDOUT' in - on line 2

Call Stack:
   18.4301     125824   1. {main}() -:0

string(6) "STDOUT"