8.4 How diff3 Merges Incomplete Lines

With ‘-m’, incomplete lines (see section Incomplete Lines) are simply copied to the output as they are found; if the merged output ends in an conflict and one of the input files ends in an incomplete line, succeeding ‘|||||||’, ‘=======’ or ‘>>>>>>>’ brackets appear somewhere other than the start of a line because they are appended to the incomplete line.

Without ‘-m’, if an ed script option is specified and an incomplete line is found, diff3 generates a warning and acts as if a newline had been present.