GMT

Let us first determine what the result should be. With -C3 we are saying that any operation should only affect column 3 (the last one). The stack is initialized to all zeros. Placing a file (or STDIN) on the stack is modulated by -C3 so that only the value 4 is actually put on the stack for column 3. Now we add 1, still just to column 3, and then we are done (=). Hence [0 0 0 5] is the correct answer. So to me the bug lies in the first case where -C3 seems to be ignored when the file is placed but honored when 1 is added. I argue that both examples should output [0 0 0 5]. Comments?

I would be surprised if the [0 0 0 5] was considered the correct result (and that independently of the implementation arguments). Actually this issue is not specific to STDIN as it happens equally with files.

echo 1 2 3 4 > lixo.dat

gmtmath -C3 1 lixo.dat ADD =
0 0 0 5

gmtmath -C3 lixo.dat 1 ADD =
1 2 3 5

I certainly would not like to see the contents of my file, in columns other than specified by -C, to be modified at all.

I already pointed out that it has nothing to do with STDIN.
Not sure what you mean though: First you seem to say that [0 0 0 5] should not be correct, but your last sentence seems to imply you only want the content of the file to be modified as specified by -C; at least that is how I read you. The way I intended -C to work is to modify which columns are allowed to be changed by arguments and operators. A file is an argument and hence only those columns in the file that pass the -C modulator gets through. That seems consistent to me. Or are you arguing that -C should NOT affect files that are placed on the stack?

Sorry if I was not clear. I meant to say that if I was a user who read the manual (which pretty closely describes how this issue applies to me) and got the [0 0 0 5] result than I would surprised, as what I would expect would be the [1 2 3 5] answer. Otherwise what good would it do to me to have a series of columns filled with zeros?

(not sure what you meant in the last sentence of -C not affecting files in stack)

And a year went by...How can we resolve this. To me, when -C3 is issued, nothing should happen to any other column until another -C option is issued. That is the whole point of having -C. So that is why I consider

echo 1 2 3 4 | gmtmath -C3 STDIN 1 ADD =
1       2       3       5

Trying this again. Perhaps this makes it clearer: What you want is the output of

echo 1 2 3 4 | gmtmath STDIN -C3 1 ADD =

echo 1 2 3 4 | gmtmath -C3 STDIN 1 ADD =

That is, you want to load all your columns from input (or file), then slam -C3 into effect and only add 1 to your last column. I on the other hand wish to exclude all but the last column from being placed on the stack in the first case. So in that case I want 0 0 0 5 on output and in your case you want 1 2 3 5.
So there is not a problem getting what you want; it is a problem getting what I want due to the bug.

All right, I follow that.