ELisp: Find Replace Text in Buffer

Search and Find Replace Functions

These search functions are used to search text, do find replace, and also move cursor to where a text occur:

• search-forward
• search-backward
• re-search-forward (alias search-backward-regexp)
• re-search-backward (alias search-forward-regexp)

The forward versions place cursor at end of match. The backward versions place cursor at begin of match.

• ELisp: Regex Functions

Find Replace Text in Buffer

Typical way to do text replacement in current buffer:

(let ((case-fold-search nil))
  ;; set case-fold-search to t, if you want to ignore case

  (goto-char (point-min))
  (while (search-forward "myStr" nil t)
    (replace-match "myReplaceStr"))

  ;; repeat for other string pairs

  ;; use re-search-forward if you want regex

  )

Case Sensitivity in Search

To control the letter case of search, locally set case-fold-search to t or nil. By default, it's t.

(let ((case-fold-search nil))
  ;; set case-fold-search to t, if you want to ignore case
  ;; search text code here
  )

Case Sensitivity in Replacement

To control letter case of the replacement, use the optional arguments in replace-match function.

(replace-match NEWTEXT &optional FIXEDCASE LITERAL STRING SUBEXP)

Use t for FIXEDCASE.

By default, the letter case used in replacement is smart. If the found text is First-cap or ALLCAPS, the replacement is accordingly.

Match Data

the begin/end positions of match, or capture, are storedin match-data.

• ELisp: Match Data (Regex Result)

Find Replace in a Region

If you need to do find replace on a region only, wrap the code with save-restriction and narrow-to-region.

;; idiom for string replacement within a region
(save-restriction
  (narrow-to-region pos1 pos2)

  (goto-char (point-min))
  (while (search-forward "myStr1" nil t)
    (replace-match "myReplaceStr1"))

  ;; repeat for other string pairs
  )

🛑 WARNING: Boundary Change After Insert/Remove text

Whenever you work in a region, remember that the position of the end boundary is changed when you add or remove text in that region.

For example, suppose {p1, p2} is the boundary of some text you are interested. After doing some change there, suppose you want to do some more change. Don't just call (something-region p1 p2) again, because p2 is no longer the correct boundary.

A good solution is to use narrow-to-region. ELisp: Save narrow-to-region

Find Replace Multiple Pairs

A package to allow easy code for to find replace multiple pairs.

• Emacs: xah-replace-pairs.el