#MATLAB, 11 bytes

!shutdown/p

Somewhat similar to Stewie Griffin's approach. However, MATLAB has way shorter ways of invoking system commands; in this case, ! is used. Windows does not need .exe for command names, so that's left out as well. The / option is still supported (I'm running Windows 10), and negates the need for the space. Alternatives are:

system shutdown/p % 17 bytes; uses so-called 'command' syntax.
dos shutdown/p    % 14 bytes; the 'dos' command can be used just as well.

MATLAB, 11 bytes

!shutdown/p

Somewhat similar to Stewie Griffin's approach. However, MATLAB has way shorter ways of invoking system commands; in this case, ! is used. Windows does not need .exe for command names, so that's left out as well. The / option is still supported (I'm running Windows 10), and negates the need for the space. Alternatives are:

system shutdown/p % 17 bytes; uses so-called 'command' syntax.
dos shutdown/p    % 14 bytes; the 'dos' command can be used just as well.

#MATLAB, 11 bytes

!shutdown/p

Somewhat similar to Stewie Griffin's approach. However, MATLAB has way shorter ways of invoking system commands; in this case, ! is used. Windows does not need .exe for command names, so that's left out as well. The / option is still supported (I'm running Windows 10), and negates the need for the space. Alternatives are:

system shutdown/p % 17 bytes; uses so-called 'command' syntax.
dos shutdown/p    % 14 bytes; the 'dos' command can be used just as well.

#MATLAB, 11 bytes

!shutdown/p

Somewhat similar to Stewie Griffin's approach. However, MATLAB has way shorter ways of invoking system commands; in this case, ! is used. Windows does not need .exe for command names, so that's left out as well. The / option is still supported (I'm running Windows 10), and negates the need for the space. Alternatives are:

system shutdown/p % 17 bytes; uses so-called 'command' syntax.
dos shutdown/p    % 14 bytes; the 'dos' command can be used just as well.

#MATLAB, 11 bytes

!shutdown/s

Somewhat similar to Stewie Griffin's approach. However, MATLAB has way shorter ways of invoking system commands; in this case, ! is used. Windows does not need .exe for command names, so that's left out as well. The / option is still supported (I'm running Windows 10), and negates the need for the space. Alternatives are:

system shutdown/s % 17 bytes; uses so-called 'command' syntax.
dos shutdown/s    % 14 bytes; the 'dos' command can be used just as well.

#MATLAB, 11 bytes

!shutdown/p

Somewhat similar to Stewie Griffin's approach. However, MATLAB has way shorter ways of invoking system commands; in this case, ! is used. Windows does not need .exe for command names, so that's left out as well. The / option is still supported (I'm running Windows 10), and negates the need for the space. Alternatives are:

system shutdown/p % 17 bytes; uses so-called 'command' syntax.
dos shutdown/p    % 14 bytes; the 'dos' command can be used just as well.