When an input file ends in a non-newline character, its last line is called an incomplete line because its last character is not a newline. All other lines are called full lines and end in a newline character. Incomplete lines do not match full lines unless differences in white space are ignored (see White Space).
An incomplete line is normally distinguished on output from a full
line by a following line that starts with ‘\’. However, the
RCS format (see RCS) outputs the incomplete line as-is,
without any trailing newline or following line. The side by side
format normally represents incomplete lines as-is, but in some cases
uses a ‘\’ or ‘/’ gutter marker. See Side by Side. The
if-then-else line format preserves a line’s incompleteness with
‘%L’, and discards the newline with ‘%l’. See Line Formats.
Finally, with the
ed and forward
output formats (see Output Formats)
represent an incomplete line, so it pretends there was a newline and
reports an error.
For example, suppose F and G are one-byte files that contain just ‘f’ and ‘g’, respectively. Then ‘diff F G’ outputs
1c1 < f \ No newline at end of file --- > g \ No newline at end of file
(The exact message may differ in non-English locales.) ‘diff -n F G’ outputs the following without a trailing newline:
d1 1 a1 1 g
‘diff -e F G’ reports two errors and outputs the following:
1c g .