(octave.info)The do-until Statement

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10.4 The do-until Statement
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The ‘do-until’ statement is similar to the ‘while’ statement, except
that it repeatedly executes a statement until a condition becomes true,
and the test of the condition is at the end of the loop, so the body of
the loop is always executed at least once.  As with the condition in an
‘if’ statement, the condition in a ‘do-until’ statement is considered
true if its value is nonzero, and false if its value is zero.  If the
value of the conditional expression in a ‘do-until’ statement is a
vector or a matrix, it is considered true only if it is non-empty and
_all_ of the elements are nonzero.

   Octave’s ‘do-until’ statement looks like this:

     do
       BODY
     until (CONDITION)

Here BODY is a statement or list of statements that we call the “body”
of the loop, and CONDITION is an expression that controls how long the
loop keeps running.

   This example creates a variable ‘fib’ that contains the first ten
elements of the Fibonacci sequence.

     fib = ones (1, 10);
     i = 2;
     do
       i++;
       fib (i) = fib (i-1) + fib (i-2);
     until (i == 10)

   A newline is not required between the ‘do’ keyword and the body; but
using one makes the program clearer unless the body is very simple.