 This behavior allows a default value to be defined for cases where a more specific value is not available.In contrast to the ternary operator used as codice_1, but like the binary Elvis operator used as codice_2, the null coalescing operator is a binary operator and thus evaluates its operands at most once, which is significant if the evaluation of codice_3 has side-effects.In Bash "If "parameter" is unset or null, the expansion of "word" is substituted.