Piping PHP file content to PHP command in CLI - php

Question

My question relate to the use of PHP in CLI. I don't know why the piping of the content of a PHP file to the PHP command works:
cat file.php | php
like in the installation of Composer Composer Installation:
curl -sS https://getcomposer.org/installer | php

Answer 1

If you don't give any argument to PHP, it reads from standard input (commonly called stdin).
If your output buffering is disabled, you can try to run php without argument, and type <?php echo "test\n"; + Enter, you'll see "test". stdin is basically the stream where your keyboard writes, and stdout is basically your terminal, where echo writes.
But the pipe ( | ) changes that behaviour : the standard output of the first program becomes the standard input of the second one.
This is a quite powerful thing our nix system shells offer :-).

Answer 2

As to "why it works": It works because the -cli variant of the PHP binary is designed to read from stdin and process input scripts from there alternatively.
The manpage lists various execution options. See the very last line:
PHP is a widely-used general-purpose scripting language that is espe‐
cially suited for Web development and can be embedded into HTML. This
is the command line interface that enables you to do the following:
You can parse and execute files by using parameter -f followed by the
name of the file to be executed.
Using parameter -r you can directly execute PHP code simply as you
would do inside a .php file when using the eval() function.
It is also possible to process the standard input line by line using
either the parameter -R or -F. In this mode each separate input line
causes the code specified by -R or the file specified by -F to be exe‐
cuted. You can access the input line by $argn. While processing the
input lines $argi contains the number of the actual line being pro‐
cessed. Further more the parameters -B and -E can be used to execute
code (see -r) before and after all input lines have been processed
respectively. Notice that the input is read from STDIN and therefore
reading from STDIN explicitly changes the next input line or skips
input lines.
If none of -r -f -B -R -F or -E is present but a single parameter
is given then this parameter is taken as the filename to parse and
execute (same as with -f). If no parameter is present then the
standard input is read and executed.

Answer 3

Normally you would not do it that way and would simply execute the file by php file.php. In this case, for whatever reason you want to do it that way, you need quotes around it with quotes
php -r "`cat file.php`"
Edit You could do this as well.
Put a hashbang at the front of the file like this
#!/usr/bin/env php
<?php
//code follows here
Then execute with
cat file.php | php