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Hello, everyone.

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In this sequence we'll look at
the API for manipulating files.

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What we'll be looking at particularly

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is how to navigate between files,

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how to create and remove files,

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how to list files in the directories,

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and how to read from
and write to files.

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To begin with,

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we need an entry point
in the file system,

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there are many.

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With "FileLocator home"
you have the user directory,

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"FileLocator root" you have the root

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of the directory system.

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With "FileLocatorC" in Windows
you have disc C:

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Once you have a directory,

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these 3 elements are directories,

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I take one, "FileLocator home"

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in which I have
the user home directory.

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From there I can say,

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"Give me your access path".

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So "home" isn't a string,
it's an object that represents

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a directory and I can say,

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"Give me the string
locating you in the system".

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So that's "home/cassou".

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I can ask a directory
where its children are.

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"What are all the files
and directories you contain?"

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Here it tells me, in "home".

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I've a file named .bashrc,

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and I've a Music directory.

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So this, "children",

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returns a bundle of objects,

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which are files and directories.

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If we play a bit more with this API,

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we'll see the method "/",

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When we send the message /

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to a directory we can indicate
a particular child that interests us.

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So "home/'Music'"
gives me the Music directory.

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By sending the message
"directories" to a file,

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I get all the sub files.

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Here I see that, in my Music library,

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I have a file Anouar_Brahem.

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The parent message allows me
to go up a rung,

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so if I'm in the Music file,

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I send "parent" but I return
to my "home" file.

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Leaving my directory

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"Music", as we saw before,
I'll try to create a directory.

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To do this, I check
if the directory exists.

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By sending a message "isDirectory"

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I see whether it exists or not.

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This says it doesn't exist.

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All right, I create it with
"ensureCreateDirectory".

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Then I test it, "do you exist?"
In this case it exists,

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with "delete" I can erase it,
and I check it's deleted

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by sending ""isDirectory".

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To find

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all the children in a directory,

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there are several methods.
I'll show you two.

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We send a message,
"allChildrenMatching" to a directory,

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and by passing it an expression

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that's typical of the ladder
and which represents

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the name of the directory we expect,
so with "*.ogg",

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I want all the files to have
the extension ".ogg".

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That will return all my music files
to .ogg in my Pink Floyd directory.

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I can do the same thing
in a more long-winded way.

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By sending the message
"allChildren" I get all the children

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all the files and directories,
in a particular directory,

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and I filter with the message "select"

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all those whose name ends in ".ogg".

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"Basename" returns the string
representing the file name

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and I want the file name
to end in .ogg.

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These two bits of code
are almost the same.

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How do we get information about a file?

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How do we create a file from a string?

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I've a file name, "asFileReference",

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which turns my file name
into a reference towards a file.

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It can be an existing
or a non-existent file, I don't know.

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Let's look at the message
"isFile" at this reference.

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I'll get "true" if it exists
and "false" if it doesn't.

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By sending the message "basename",
I get the name of the file.

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By sending "extension"
I get the file extension,

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with "size" I get the size,

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and with "PathString",
as we saw before,

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I get the access path
in the form of a string.

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Now let's see how to write to
and read from a file. To write,

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first of all, I take
a reference towards a file.

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Here, I check that it doesn't exist.

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We can write to a file that exists,
I'm checking it doesn't exist.

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I write to it.
To write, I create a stream.

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With "nextPutAll"

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I ask to write each character
of the stream to the file.

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At the end I close my stream
to ensure that the system

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has written everything to the disc.

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Conversely, I can read

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from a file,
so I take the same file and .txt.

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I check it exists, and it does,
because I can write to it.

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I create a "ReadStream"

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and I look, either character
by character by sending "next".

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With the message "next" I'll get,
"h" then "e" then "l", etc...

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I do "next" once, I get "h".

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Afterwards I'll pick up everything,

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from the first "h" I've just read
to the end of the file.

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Here I get "ello World"
without the "h".

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At the end, I send "stream close"
to the stream object,

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to ensure the file reference is closed.

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We can write these codes more simply,

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without having the need

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to send the "close" message.

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We might forget to send
the "close" message.

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There can be an exception
that means "close" is never sent.

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In general, we try to avoid
having to write it ourselves.

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To do this, to write,

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I take my file reference,

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I send the message "writeStreamDo",

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which takes a block in parentheses,

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the block takes one stream
in parentheses.

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This stream will be automatically
provided by "writeStreamDo"

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which will create a
"writeStream" on the file.

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The only thing I need to do is,
by using this stream,

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manipulate the stream
to do what I want with the file.

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I'll write 'Hello World' to the file,
"stream nextPutAll: 'Hello World'".

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When the block finishes,

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the stream closes automatically,
and the file writes to the disc.

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Same principle for reading,
I put "readStreamDo".

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Here I have a stream,
I can do what I want with it.

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I decide to retrieve
the contents of the stream.

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What you should know,

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is that files and directories
are references,

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they're references towards
files and directories on the disc

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that may or may not exist.
Check with "isFile", "isDirectory"

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if the files exist on the disc.

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The API is simple,

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and facilitates navigation
and manipulation of the files.

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We can read from and write to files
through streams,

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and with an API

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which will close the stream
automatically at the end.