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The run instruction will execute
the command of your choosing while

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building the image.

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The command will be run exactly as if you
had typed in a shell on the guest OS.

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You can use these commands to permanently
update the contents of the image.

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Run is useful for
installing dependencies or

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running a script in
the container at build time.

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This pair of commands here both run
the ubuntu apps get package manager.

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The first updates the list
of available packages and

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the second uses that updated
list to install python3.

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The form of one instruction shown here is
called the shell form which will execute

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the given command using a shell like bash.

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You should use this form if there
are environment variables or

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file name wild cards whose values you
want substituted into the command.

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The second form of RUN
is called the exec form.

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Let me convert this first
instruction to exec form.

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We use JSON array syntax
with square brackets.

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We'll surround each element
with quotation marks and

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we'll separate the elements with commas.

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The first element should be
the executable you want to run,

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in this case that's apt-get.

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All subsequent elements
are arguments to that executable.

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The exec form just passes your parameters
directly to the given executable

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without invoking a shell or
doing any substitution.

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You should use the exec form if you want
to be very precise about the arguments you

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pass to the executable.

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So to finish converting this one, we'll
use update as our second argument and

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-y as our third.

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And this run instruction in exec form
is identical in meaning to this run

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instruction in shell form.