If you would just tell us the constraints under which you want to assign one of a group of values to a variable, we can probably help you construct a single command using one or more ternary expressions to get what you want. But just saying "I want to set a default value like bash does." doesn't really make sense. The awk utility doesn't have the concept of an "unset" scalar variable. (It does for elements of an array variable; but not for scalar variables.) And, in awk the empty string and the string "0" and the number 0 will be treated as identical in many awk expressions. But, if we know explicitly what you are trying to do we can differentiate between unset array elements, an empty string, and a 0 (although you can't differentiate a string 0 from a number 0 in awk). And, if you reference an array element (other than by using the in operator), you create that array element. For instance, if you split a line using:

Code:

n = split($0, a, ",")

and you want to set the variable v to "unset" if array[5] has not been set (i.e., split() returned a value less than 5), "empty" if a[5] is an empty string, "zero" if a[5] compares equal to 0 (such as with "0", "000", or "0.0"), and to the contents of a[5] for anything else you could use:

Code:

v = (5 in a) ? a[5] == "" ? "empty" : a[5] == 0 ? "zero" : a[5] : "unset"

The command:

Code:

b=""; a=b?b:"Default"

sets a to Default because the ternary operator evaluates the 1st expression (b in this case) and if that expression evaluates to TRUE returns the 2nd expression; otherwise it returns the 3rd expression. In awk a variable evaluates to TRUE if it is a non-zero string, a non-zero number, or a non-empty string; otherwise, it evaluates to FALSE.

Scalar variables in awk are never "unset" as in a shell variable that has never been set. In awk, every unset scalar variable has the value 0 if it is referenced as a numeric value and has the value empty string if referenced as a string.