Difference between "on the command line" and "at the command line"

Solution 1:

I would say that, when the command line is in front of you, you are at the command line. (Or you are at a command prompt, or in a terminal window. Etc.)

Whatever you type is on the command line.

Solution 2:

I don't think there is any difference in meaning or "correctness" between the two forms. Personally I use at the command line, and until just now I assumed most people did the same. But apparently I'm in the minority...

Solution 3:

There may be an interaction here between "on the command line" and "at the command prompt". In the situation in which these expressions are typically used, namely when explaining to someone what to type into a command shell window, they effectively mean the same thing. People may be mixing them up. This is supported by the almost identical frequencies of "at the command prompt" and "at the command line":