How do I search for, delete, or replace unprintable (eight-bit or control) characters?
To search for a single character that appears in the buffer as, for example, `\237′, you can type C-s C-q 2 3 7. (This assumes the value of search-quote-char is 17 (i.e., C-q).) Searching for all unprintable characters is best done with a regular expression (regexp) search. The easiest regexp to use for the unprintable chars is the complement of the regexp for the printable chars. • Regexp for the printable chars: `[\t\n\r\f -~]’ • Regexp for the unprintable chars: `[^\t\n\r\f -~]’ To type these special characters in an interactive argument to isearch-forward-regexp or re-search-forward, you need to use C-q. (`\t’, `\n’, `\r’, and `\f’ stand respectively for TAB, LFD, RET, and C-l.) So, to search for unprintable characters using re-search-forward: M-x re-search-forward RET [^ TAB C-q LFD C-q RET C-q C-l SPC -~] RET Using isearch-forward-regexp: M-C-s [^ TAB LFD C-q RET C-q C-l SPC -~] To delete all unprintable characters, simply use replace-regexp: M-x replace-regexp RET [^ TAB C-q LFD
