Detect optional function argument (array)

Question

Consider this function:

function add_one(in_ar, each) { for (each in in_ar) { in_ar[each]++ } } 

I would like to modify it such that if a second array is provided, it would be used instead of modifying the input array. I tried this:

function add_one(in_ar, out_ar, each) { if (out_ar) { for (each in in_ar) { out_ar[each] = in_ar[each] + 1 } } else { for (each in in_ar) { in_ar[each]++ } } } BEGIN { split("1 2 3 4 5", q) add_one(q, z) print z[3] } 

but I get this result:

fatal: attempt to use scalar `z' as an array 

Answer 1

There are 2 problems in your script

• the variable z isn't initialized
• the test if(out_ar) in your second code snippet is not suited for arrays

To solve the first problem, you need to assign an array element (like z[1]=1) since there is no array declaration in awk. (You can't use similar statement like declare -A as you would do in bash).

The second problem can be solved, provided you're using GNU awk, with the function isarray() or typeof().

So your code should look like this:

function add_one(in_ar, out_ar, each) { if (isarray(out_ar)) { for (each in in_ar) { out_ar[each] = in_ar[each] + 1 } } else { for (each in in_ar) { in_ar[each]++ } } } BEGIN { split("1 2 3 4 5", q) z[1]=1 add_one(q, z) print z[3] } 

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