It is easy to leave unnecessary spaces at the end of a line, or empty lines at the end of a buffer, without realizing it. In most cases, this trailing whitespace has no effect, but sometimes it can be a nuisance.
You can make trailing whitespace at the end of a line visible by
setting the buffer-local variable show-trailing-whitespace to
t. Then Emacs displays trailing whitespace, using the face
This feature does not apply when point is at the end of the line containing the whitespace. Strictly speaking, that is trailing whitespace nonetheless, but displaying it specially in that case looks ugly while you are typing in new text. In this special case, the location of point is enough to show you that the spaces are present.
Type M-x delete-trailing-whitespace to delete all trailing
whitespace. This command deletes all extra spaces at the end of each
line in the buffer, and all empty lines at the end of the buffer; to
ignore the latter, change the variable delete-trailing-lines to
nil. If the region is active, the command instead deletes
extra spaces at the end of each line in the region.
On graphical displays, Emacs can indicate unused lines at the end of
the window with a small image in the left fringe (see Fringes).
The image appears for screen lines that do not correspond to any
buffer text, so blank lines at the end of the buffer stand out because
they lack this image. To enable this feature, set the buffer-local
variable indicate-empty-lines to a non-
nil value. You
can enable or disable this feature for all new buffers by setting the
default value of this variable, e.g.,
Whitespace mode is a buffer-local minor mode that lets you visualize many kinds of whitespace in the buffer, by either drawing the whitespace characters with a special face or displaying them as special glyphs. To toggle this mode, type M-x whitespace-mode. The kinds of whitespace visualized are determined by the list variable whitespace-style. Individual elements in that list can be toggled on or off in the current buffer by typing M-x whitespace-toggle-options. Here is a partial list of possible elements (see the variable’s documentation for the full list):
Enable all visualizations which use special faces. This element has a
special meaning: if it is absent from the list, none of the other
visualizations take effect except
Highlight trailing whitespace.
Highlight tab characters.
Highlight space and non-breaking space characters.
Highlight lines longer than 80 columns. To change the column limit, customize the variable whitespace-line-column.
Highlight empty lines.
Highlight too-deep indentation. By default any sequence of at least 4
consecutive TAB characters or 32 consecutive SPC characters is
highlighted. To change that, customize the regular expression
Draw space and non-breaking characters with a special glyph.
Draw tab characters with a special glyph.
Draw newline characters with a special glyph.
Global Whitespace mode is a global minor mode that lets you visualize whitespace in all buffers. To toggle individual features, use M-x global-whitespace-toggle-options.