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- So we have already talked
a little bit about register.

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Register is particularly
useful in combination

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with when statements.

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Let's go check it out.

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So you can use register to
store the output of a command

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and address it as a variable.

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And next, you can use
the result of the command

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in a conditional or in a loop,

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and that's exactly what I want to show you

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in the next couple of examples.

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So the first example
is command output test

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and we are going to run that on ansible1.

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So what are we going to do?

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Well, the command that we
are running is vgs centos.

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So this is running vgs,
that's a Linux command,

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that checks if volume groups are available

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and it is running vgs on centos.

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So this command will give
you some useful information

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if the volume group exists,

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and if it doesn't exist it'll
give you other information.

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In order to work with it,

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we register the complete
output of the command

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in a variable, and this variable is vgout.

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I do want this playbook to continue

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even if there is no result

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and that is why you can
see ignore_errors is true.

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Notice that ignore_errors
can be set in a play header,

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can also be set in a task header.

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Here it has a task scope.

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So only for this task, if it
has an error, we continue.

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If all the tasks have an error

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then the playbook execution will stop

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and produce a normal error
behavior that we've seen before.

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Next, I'm using show variable value.

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I like using debug especially
if you are using register.

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Register can give you results

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that you would never have expected before.

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So it's a wise idea to go check out

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what exactly register is giving you.

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So we have debug var vgout.

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It'll show you the values that
are in the register variable.

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And then, we are going to print a message

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and we print a message.

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Again, we see debug.

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The message is vg does not exist

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when "not found" in vgout.standard error.

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So what's happening here?

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We are looking for the
string text "not found"

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in the registered variable
vgout.standard error.

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A notice by the way that
in a when statement,

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you do not have to use the curly braces

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to refer to the variables.

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It's a little bit confusing,
but it's just the rule

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when using variables in when statements.

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Let's go see how this is working.

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So here we can see the fact gathering.

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You can see that the test for
the VG existence is failing.

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And then, you can see that basically

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everything that you see right here

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is in a nicely printed
format in the variable vgout.

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So vgout is showing you the commands.

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It is showing you the standard out.

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Oh, there is no standard out.

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It is showing you the standard error,

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nicely formatted in lines

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and the standard error all by itself.

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And then, we get the
message "vg does not exist".

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Now, let's rewrite this playbook

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to the situation where the
volume group does exist.

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So quick command on ansible1 -a vgs.

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And there, we can see that the name

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of the volume group is rl,

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rl for Rocky Linux.

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So this time the command is vgs rl.

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There we go.

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We run it again.

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And, we can see this is kind of curious,

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test for VG existence.

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I'm learning a command

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and nevertheless I'm getting changed,

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that's one of the weird artifacts

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of using the command model.

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We'll talk about it later.

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There's a change to when statement

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that you can use to influence that.

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Here we can see the command.

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Here we can see the standard out

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and the standard out
actually does contain rl.

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There we go.

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We're looking for the string

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or the partial string to
appear in the standard out.

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So the print methods can be skipped.

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I have another example
which is register_command.

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So what are we doing here?

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We are prompting for a username.

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Oh, if we are prompting for a username

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then definitely I want
private to be set to no

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because by default vars_prompt
will not show the results

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of what the user is typing,

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that's not very user friendly

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and there's no reason to
make this username private.

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So let's show it.

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Then, we are using the
shell command cat/etc/passwd

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and we are register the
output of that command

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on passwd_contents.

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Next, we have the debug module
again on passwd_contents.

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And then,

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we are printing "passwd
contains user {{username}}".

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So that's the username that
was created in vars_prompt.

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And then, we have the when statement

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and the when statement is a curious one,

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passwd_content.stdout.

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That is what we are looking for.

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And next, we are using the
Python function find username.

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This is Python.

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This is a Python command

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that is used on the standard
out on the register variable.

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You can see that because
username between braces,

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that's one notation of variables
we haven't seen before,

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but the username between braces

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that's the Python way
to refer to a variable

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and we look for non equals minus one.

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Hey, what is this is minus one?

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Well, you should know that
if this Python find function

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will find the username,

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it'll give a byte offset

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like 386 if the user was
find starting at byte 386.

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And if user was not found,

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then it'll give a minus one.

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We want the message to
print "passwd contains user"

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when we get a byte offset.

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We don't know the byte offset beforehand

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but we do know if the user was found,

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we do not see minus one

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and that is what's happening right here.

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So let's run it.

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Let's first run it on user, user ansible,

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that's a user that does exist.

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And there we can see, we get
passwd contains user ansible.

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Of course it contains user ansible.

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Just for your convenience,

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we can see the standard out,

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nicely formatted in lines

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which makes it a little bit more readable.

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There we have the lines

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and we can see all the other details

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that is just interesting to check it up.

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But this debug of the
entire registered variable

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obviously has no real function.

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The only function is to clarify

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to yourself what is happening.

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Now, let me use it again with
a user that does not exist

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and there we get a
skipping and a skipping.

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It's still printing the entire variable

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that is because we are
looking at the register okay?

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The register is just printing
the output of etc/passwd

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and we don't do anything
conditional on that.

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But here in this last
task in the playbook,

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let me show you again, in this
last task in the playbook,

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the when statement is find(username)

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should not return a minus one.

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Well, Caroline doesn't exist
so we do get a minus one,

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and that is why we get a skipping,

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and that is how you can use register.

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Register is an awesome command,

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and you are likely going to use it a lot

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when working with ansible.