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>> SPEAKER: Let's write a program in PHP.

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Unlike C, which is a compiled language,
PHP is an interpreted

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language, which means as soon as we
write our source code in PHP, we can

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simply run it by passing that source
code as input into what's called an

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interpreter, a program whose purpose
in life is to read your PHP source

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code, top to bottom, left to right, and
do, line-by-line, whatever it is

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you've set it to do.

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Here, in a file called hello.php,
let me begin as follows.

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Open bracket, question mark, php, and
then down below, let me close that php

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tag with question mark, angle bracket.

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>> Now you'll find, on some computers, you
can actually get away with just

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doing open bracket, question mark,
without the trailing php.

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But you'll find that your code is more
portable and runs on more computers if

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you do use this more verbose version.

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Now, in-between these tags, let's do
something simple, like printf, quote

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unquote, "hello world",
with a backslash n.

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>> Let's now save the file
and run this program.

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But to run this file, we're going to
have to pass it through the PHP

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interpreter.

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So technically, we're running PHP, and
passing as input the source code I

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just wrote.

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To do this, at my command prompt,
I'll do php hello.php.

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And there we see, hello world.

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>> Of course, to run this program, I had
to know that the program was written

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in PHP, so that I'd know
to run its interpreter.

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This certainly is an ideal, especially
when, in C, after compiling a program,

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a user can just run it without having
to know or care that it was once

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written in C. But we can achieve that
same effect with PHP as well.

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>> Let's go back to my source code.

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At the very top of this file, let's
add a shebang, a sharp bang or

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exclamation point, followed by slash
bin slash php, which is simply the

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path to the PHP interpreter or program
on this particular computer.

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Let's now save the file, but also
make the file executable

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in addition to readable.

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It suffices for a file to be readable
for a program like PHP to interpret

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it, but to actually run a program and
look for that shebang at the top of it

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to know what interpreter to use to
execute the code, we have to make the

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file executable as well.

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>> To do this, let's type chmod a plus
x, for executable, hello.php.

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And now, let's run dot
slash hello.php.

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And again, we see hello world.

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Now we can take this one step further.

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We don't have to reveal to the world
that this program, hello world, is

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written in PHP.

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We can remove that file extension now
as well by specifying mv hello.php,

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shall be renamed simply hello, and I
can now do dot slash hello, and I

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again see hello world.

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>> Let's take this one final step.

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Suppose that I don't necessarily know
the path to PHP on the computer on

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which this program might be run, but I
want the computer to find it for me.

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It turns out that on a lot of computers,
there's a program called

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env for environment, E-N-V, that
can figure that out for us.

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So let's go back to the shebang and
change it to be simply env space php.

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This new shebang will instruct the
computer to check its environment for

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the program, PHP, and if it's there,
use that to interpret this program.

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