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How `diff3' Merges Incomplete Lines
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With `-m', incomplete lines (see 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.