Showing whitespace in Ed

Question

In Ed I can test for whitespace with this regex: g/ *$/p. I don't suppose there is a way of showing whitespace, perhaps by passing the contents of the buffer to another shell command?

Answer 1

You may use the l ("ell") command in ed (and in sed, vi, and ex too, BTW) to display lines in a visually unambiguous form. The command is used analogous to the p and n commands but shows end-of-line as $, tabs as \t, and carriage returns as \r (there are some other special characters that are similarly marked up too, see the POSIX specification). Spaces are shown as-is:

a
this line ends with two spaces and a tab    
.
l
this line ends with two spaces and a tab  \t$

If you want to list all lines that have spaces at the end of them and display these with their line number and with l:

g/ $/ ln

You may also pipe the contents of the buffer, or any range of lines, to your system's cat command, if it knows how to display lines in a similar way to the l command in ed, e.g. w ! cat -A with BusyBox's cat, or w ! cat -v with OpenBSD's cat (which will do even more markup of the text).

If you want to see spaces, as in "replace every space with some visually catching character, like *", you can do that in ed with the s command on the current line:

s/ /*/gp

... or on all lines that contain a space:

g/ / s//*/gn

(I'm using n in place of p there to make it easier to locate the lines in the document.)