In scalar context, the .. operator with numeric constants is interpreted as line range. As you are reading lines with -n and you are on the first line, 1..3 evaluates to 1. All other ranges evaluate to undef (stringified to ''), because the first line is out of the range, and that's why you get the warning.

In reply to Re^5: Editing just one column in a file by choroba
in thread Editing just one column in a file by ZWcarp

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