Emacs Lisp: Replace HTML Entities

Here's commands to replace HTML entities to character or reverse.

Escape HTML Chars to Entities

Here's a command to replace < > & to entities < > & or reverse.

(defun xah-html-escape-char-to-entity (@begin @end &optional @entity-to-char-p)
  "Replace HTML chars & < > to HTML entities on current text block or selection.
The string replaced are:
 & ⇒ &amp;
 < ⇒ &lt;
 > ⇒ &gt;

Highlight changed places.
If `universal-argument' is called first, the replacement direction is reversed.

When called in lisp code, @begin @end are region begin/end positions. If @entity-to-char-p is true, reverse change direction.

URL `http://xahlee.info/emacs/emacs/elisp_replace_html_entities_command.html'
Version 2020-08-30"
  (interactive
   (save-excursion
     (list
      (if (use-region-p)
          (region-beginning)
        (progn
          (re-search-backward "\n[ \t]*\n" nil "move")
          (re-search-forward "\n[ \t]*\n" nil "move")
          (point)))
      (if (use-region-p)
          (region-end)
        (progn
          (re-search-forward "\n[ \t]*\n" nil "move")
          (re-search-backward "\n[ \t]*\n" nil "move")
          (point)))
      (if current-prefix-arg t nil))))
  (let (($changedItems '())
        ($findReplaceMap
         (if @entity-to-char-p
             ;; this to prevent creating a replacement sequence out of blue
             [
              ["&amp;" "螽⛫1"] ["&lt;" "螽⛫2"] ["&gt;" "螽⛫3"]
              ["螽⛫1" "&"] ["螽⛫2" "<"] ["螽⛫3" ">"]
              ]
           [ ["&" "&amp;"] ["<" "&lt;"] [">" "&gt;"] ]
           )))
    (save-excursion
      (save-restriction
        (narrow-to-region @begin @end)
        (let ( (case-fold-search nil))
          (mapc
           (lambda ($x)
             (goto-char (point-min))
             (while (search-forward (elt $x 0) nil t)
               (push (format "%s %s" (point) $x) $changedItems)
               (replace-match (elt $x 1) "FIXEDCASE" "LITERAL")
               (overlay-put (make-overlay (- (point) (length (elt $x 1))) (point)) 'font-lock-face '(:foreground "red"))))
           $findReplaceMap))))))

Named Entities to Unicode

Replace HTML named entities such as é to its Unicode character é.

(defun xah-html-named-entity-to-char (@begin @end)
  "Replace HTML named entity to Unicode character in current text block or selection.
Changed places are highlighted.
For example, “©” becomes “©”.
The following HTML Entities are not replaced: & < >

When called in lisp code, @begin @end are region begin/end positions.

URL `http://xahlee.info/emacs/emacs/elisp_replace_html_entities_command.html'
Version 2020-08-30"
  (interactive
   (if (use-region-p)
       (list (region-beginning) (region-end))
     (save-excursion
       (list
        (progn
          (search-backward "\n\n" nil "NOERROR" )
          (search-forward "\n\n" nil "NOERROR")
          (point))
        (progn
          (search-forward "\n\n" nil "NOERROR")
          (search-backward "\n\n" nil "NOERROR" )
          (point))))))
  (let (
        ($replaceMap
         [
          [" " " "] [" " " "] [" " " "] [" " " "]
          ["‏" "‏"] ["‎" "‎"] ["‍" "‍"] ["‌" "‌"]

          ["¡" "¡"] ["¢" "¢"] ["£" "£"] ["¤" "¤"] ["¥" "¥"]
          ["¦" "¦"] ["§" "§"] ["¨" "¨"] ["©" "©"] ["ª" "ª"]
          ["«" "«"] ["¬" "¬"] ["­" "­"] ["®" "®"] ["¯" "¯"]
          ["°" "°"] ["±" "±"] ["²" "²"] ["³" "³"] ["´" "´"]
          ["µ" "µ"] ["¶" "¶"] ["·" "·"] ["¸" "¸"] ["¹" "¹"]
          ["º" "º"] ["»" "»"] ["¼" "¼"] ["½" "½"]
          ["¾" "¾"] ["¿" "¿"]

          ["À" "À"] ["Á" "Á"] ["Â" "Â"] ["Ã" "Ã"] ["Ä" "Ä"]
          ["Å" "Å"] ["Æ" "Æ"] ["Ç" "Ç"] ["È" "È"] ["É" "É"]
          ["Ê" "Ê"] ["Ë" "Ë"] ["Ì" "Ì"] ["Í" "Í"] ["Î" "Î"]
          ["Ï" "Ï"] ["Ð" "Ð"] ["Ñ" "Ñ"] ["Ò" "Ò"] ["Ó" "Ó"]
          ["Ô" "Ô"] ["Õ" "Õ"] ["Ö" "Ö"] ["×" "×"] ["Ø" "Ø"]
          ["Ù" "Ù"] ["Ú" "Ú"] ["Û" "Û"] ["Ü" "Ü"] ["Ý" "Ý"]
          ["Þ" "Þ"] ["ß" "ß"] ["à" "à"] ["á" "á"] ["â" "â"]
          ["ã" "ã"] ["ä" "ä"] ["å" "å"] ["æ" "æ"] ["ç" "ç"]
          ["è" "è"] ["é" "é"] ["ê" "ê"] ["ë" "ë"] ["ì" "ì"]
          ["í" "í"] ["î" "î"] ["ï" "ï"] ["ð" "ð"] ["ñ" "ñ"]
          ["ò" "ò"] ["ó" "ó"] ["ô" "ô"] ["õ" "õ"] ["ö" "ö"]

          ["÷" "÷"] ["ø" "ø"] ["ù" "ù"] ["ú" "ú"] ["û" "û"]
          ["ü" "ü"] ["ý" "ý"] ["þ" "þ"] ["ÿ" "ÿ"] ["ƒ" "ƒ"]

          ["Α" "Α"] ["Β" "Β"] ["Γ" "Γ"] ["Δ" "Δ"] ["Ε" "Ε"]
          ["Ζ" "Ζ"] ["Η" "Η"] ["Θ" "Θ"] ["Ι" "Ι"] ["Κ" "Κ"]
          ["Λ" "Λ"] ["Μ" "Μ"] ["Ν" "Ν"] ["Ξ" "Ξ"] ["Ο" "Ο"]
          ["Π" "Π"] ["Ρ" "Ρ"] ["Σ" "Σ"] ["Τ" "Τ"] ["Υ" "Υ"]
          ["Φ" "Φ"] ["Χ" "Χ"] ["Ψ" "Ψ"] ["Ω" "Ω"] ["α" "α"]
          ["β" "β"] ["γ" "γ"] ["δ" "δ"] ["ε" "ε"] ["ζ" "ζ"]
          ["η" "η"] ["θ" "θ"] ["ι" "ι"] ["κ" "κ"] ["λ" "λ"]
          ["μ" "μ"] ["ν" "ν"] ["ξ" "ξ"] ["ο" "ο"] ["π" "π"]
          ["ρ" "ρ"] ["ς" "ς"] ["σ" "σ"] ["τ" "τ"] ["υ" "υ"]
          ["φ" "φ"] ["χ" "χ"] ["ψ" "ψ"] ["ω" "ω"] ["ϑ" "ϑ"]
          ["ϒ" "ϒ"] ["ϖ" "ϖ"]

          ["•" "•"] ["…" "…"] ["′" "′"] ["″" "″"] ["‾" "‾"]
          ["⁄" "⁄"] ["℘" "℘"] ["ℑ" "ℑ"] ["ℜ" "ℜ"] ["™" "™"]
          ["ℵ" "ℵ"] ["←" "←"] ["↑" "↑"] ["→" "→"] ["↓" "↓"]
          ["↔" "↔"] ["↵" "↵"] ["⇐" "⇐"] ["⇑" "⇑"] ["⇒" "⇒"]
          ["⇓" "⇓"] ["⇔" "⇔"] ["∀" "∀"] ["∂" "∂"] ["∃" "∃"]
          ["∅" "∅"] ["∇" "∇"] ["∈" "∈"] ["∉" "∉"] ["∋" "∋"]
          ["∏" "∏"] ["∑" "∑"] ["−" "−"] ["∗" "∗"] ["√" "√"]
          ["∝" "∝"] ["∞" "∞"] ["∠" "∠"] ["∧" "∧"] ["∨" "∨"]
          ["∩" "∩"] ["∪" "∪"] ["∫" "∫"] ["∴" "∴"] ["∼" "∼"]
          ["≅" "≅"] ["≈" "≈"] ["≠" "≠"] ["≡" "≡"] ["≤" "≤"]
          ["≥" "≥"] ["⊂" "⊂"] ["⊃" "⊃"] ["⊄" "⊄"] ["⊆" "⊆"]
          ["⊇" "⊇"] ["⊕" "⊕"] ["⊗" "⊗"] ["⊥" "⊥"] ["⋅" "⋅"]
          ["⌈" "⌈"] ["⌉" "⌉"] ["⌊" "⌊"] ["⌋" "⌋"] ["⟨" "〈"]
          ["⟩" "〉"] ["◊" "◊"] ["♠" "♠"] ["♣" "♣"] ["♥" "♥"]
          ["♦" "♦"] [""" "\""] ["Œ" "Œ"] ["œ" "œ"] ["Š" "Š"]
          ["š" "š"] ["Ÿ" "Ÿ"] ["ˆ" "ˆ"] ["˜" "˜"] ["–" "–"]
          ["—" "—"] ["‘" "‘"] ["’" "’"] ["‚" "‚"] ["“" "“"]
          ["”" "”"] ["„" "„"] ["†" "†"] ["‡" "‡"] ["‰" "‰"]
          ["‹" "‹"] ["›" "›"] ["€" "€"]
          ]))
    (save-restriction
      (narrow-to-region @begin @end)
      (let ( (case-fold-search nil))
        (mapc
         (lambda ($x)
           (goto-char (point-min))
           (while (search-forward (elt $x 0) nil t)
             (replace-match (elt $x 1))
             (overlay-put (make-overlay (- (point) (length (elt $x 1))) (point)) 'font-lock-face '(:foreground "red"))))
         $replaceMap)))))

Escape HTML Chars to Unicode

Sometimes it's useful to convert the HTML entities to special unicode chars, to avoid the whole encoding/decoding/entities complexity.

(defun xah-html-escape-char-to-unicode (@begin @end &optional @fullwidth-to-ascii-p)
  "Replace chars < > & to fullwidth version ＜ ＞ ＆ in current text block or selection.

Highlight changed places.
If `universal-argument' is called first, the replacement direction is reversed.

When called in lisp code, @begin @end are region begin/end positions. If @fullwidth-to-ascii-p is true, reverse change direction.

URL `http://xahlee.info/emacs/emacs/elisp_replace_html_entities_command.html'
Version 2020-08-30"
  (interactive
   (list
    (if (use-region-p)
        (region-beginning)
      (progn
        (re-search-backward "\n[ \t]*\n" nil "move")
        (re-search-forward "\n[ \t]*\n" nil "move")
        (point)))
    (if (use-region-p)
        (region-end)
      (progn
        (re-search-forward "\n[ \t]*\n" nil "move")
        (re-search-backward "\n[ \t]*\n" nil "move")
        (point)))
    (if current-prefix-arg t nil)))
  (let (($findReplaceMap
         (if @fullwidth-to-ascii-p
             [ ["＆" "&"] [ "＜" "<"] [ "＞" ">"] ]
           [ ["&" "＆"] ["<" "＜"] [">" "＞"] ]
           )))
    (save-excursion
      (save-restriction
        (narrow-to-region @begin @end)
        (mapc
         (lambda ($x)
           (goto-char (point-min))
           (while (search-forward (elt $x 0) nil t)
             (replace-match (elt $x 1))
             (overlay-put (make-overlay (- (point) (length (elt $x 1))) (point)) 'font-lock-face '(:foreground "red"))))
         $findReplaceMap)))))