how to search and replace an entire word?

Question

I know the command isearch-forward-word, but there doesn't seem to be an isearch-replace-word. I'd like to search and replace every instance of a certain word in a buffer. For instance, search for every instance of i and replace with I.

I found this answer, which seems to allow a digit argument, but I just want to replace every instance in my buffer.

Answer 1

You don't need to define a separate function (command) for this. And even if you did define one, it need not use query-replace-regexp.

The standard command query-replace does just what you request, if you provide it with a prefix argument.

So just use C-u M-% to query-replace words.

C-h f query-replace tells you this (note the part in bold):

query-replace is an interactive compiled Lisp function in `replace.el'.

It is bound to M-%, <menu-bar> <edit> <replace> <query-replace>.

(query-replace FROM-STRING TO-STRING &optional DELIMITED START END BACKWARD)

Replace some occurrences of FROM-STRING with TO-STRING. As each match is found, the user must type a character saying what to do with it. For directions, type C-h at that time.

In Transient Mark mode, if the mark is active, operate on the contents of the region. Otherwise, operate from point to the end of the buffer.

Use M-n to pull the last incremental search string to the minibuffer that reads FROM-STRING, or invoke replacements from incremental search with a key sequence like C-s C-s M-% to use its current search string as the string to replace.

Matching is independent of case if case-fold-search is non-nil and FROM-STRING has no uppercase letters. Replacement transfers the case pattern of the old text to the new text, if case-replace and case-fold-search are non-nil and FROM-STRING has no uppercase letters. (Transferring the case pattern means that if the old text matched is all caps, or capitalized, then its replacement is upcased or capitalized.)

Ignore read-only matches if query-replace-skip-read-only is non-nil, ignore hidden matches if search-invisible is nil, and ignore more matches using isearch-filter-predicate.

If replace-lax-whitespace is non-nil, a space or spaces in the string to be replaced will match a sequence of whitespace chars defined by the regexp in search-whitespace-regexp.

Third arg DELIMITED (prefix arg if interactive), if non-nil, means replace only matches surrounded by word boundaries. A negative prefix arg means replace backward.

Fourth and fifth arg START and END specify the region to operate on.

To customize possible responses, change the bindings in query-replace-map.

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And if you insist that you want a separate command for this, then just do the obvious:

(defun q-r-word ()
  "Query-replace whole words."
  (interactive)
  (let ((current-prefix-arg  t))
    (call-interactively #'query-replace)))

Answer 2

Run query-replace-regexp with '\bi\b' as the query and 'I' as the replacement.

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(Update to comment)

The function @lawlist linked to should work nicely if you want to replace all instances without questions. To still be prompted for each instance, below should do

(defun query-replace-word (word new-word)
  (interactive "sWord: \nsNew word: ")
  (query-replace-regexp (format "\\b%s\\b" word) new-word))

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(Update in response to Drew's answer)

Doh. See Drew's better answer. I didn't know that this could be done with a prefix argument to query-replace.