% typeset -Z3 i % echo ${i=5} 005 % echo ${i:=15} 005 % echo ${i::=15} 15 The manpage says ${name::=word} In the first form, if name is unset then set it to word; in the second form, if name is unset or null then set it to word; and in the third form, unconditionally set name to word. In all forms, the value of the parameter is then substituted. which to me doesn't imply that the parameter is reset first, especially since it isn't reset for the first form. I'm a little confused as to why this doesn't assign the value either: % unset i % typeset -Z3 i % echo ${i:=25} but this does set it: % unset i % typeset i % echo ${i:=25} 25 I thought maybe -Z3 causes the implicit value to be 000 but it is printed as empty, so shouldn't it fulfil the "unset or null" condition despite the -Z flag being active? -- Mikael Magnusson