Difference between until and while in Linux?

Answer 1

Both loop constructs have the same syntax:

while [test expression]

do

commands

done

until [test expression]

do

commands

done

Where they differ is that the 'while' loop only executes where the test expression evaluates as True, whereas the 'until' loop executes where the expression evaluates as False.

Functionally, you could achieve the same result using either loop construct by altering the test expression. Eg.:

while [n -gt 5] #n is greater than 5

is functionally identical to

until [n -le 5] #n is less than or equal to 5