Add change-header-lines action to dynamically change --header-lines

All input lines now enter the chunklist with sequential indices, and
header lines are excluded from matching via Pattern.startIndex and
PassMerger offset. This allows the number of header lines to be changed
at runtime with change-header-lines(N), transform-header-lines, and
bg-transform-header-lines actions.

- Remove EvtHeader event; header items are read directly from chunks
- Add startIndex to Pattern and PassMerger for skipping header items
- Add targetIndex field to Terminal for cursor repositioning across
  header-lines changes

Close #4659

src/actiontype_string.go

@@ -30,161 +30,164 @@ func _() {
 	_ = x[actChangeBorderLabel-19]
 	_ = x[actChangeGhost-20]
 	_ = x[actChangeHeader-21]
-	_ = x[actChangeFooter-22]
-	_ = x[actChangeHeaderLabel-23]
-	_ = x[actChangeFooterLabel-24]
-	_ = x[actChangeInputLabel-25]
-	_ = x[actChangeListLabel-26]
-	_ = x[actChangeMulti-27]
-	_ = x[actChangeNth-28]
-	_ = x[actChangePointer-29]
-	_ = x[actChangePreview-30]
-	_ = x[actChangePreviewLabel-31]
-	_ = x[actChangePreviewWindow-32]
-	_ = x[actChangePrompt-33]
-	_ = x[actChangeQuery-34]
-	_ = x[actClearScreen-35]
-	_ = x[actClearQuery-36]
-	_ = x[actClearSelection-37]
-	_ = x[actClose-38]
-	_ = x[actDeleteChar-39]
-	_ = x[actDeleteCharEof-40]
-	_ = x[actEndOfLine-41]
-	_ = x[actFatal-42]
-	_ = x[actForwardChar-43]
-	_ = x[actForwardWord-44]
-	_ = x[actForwardSubWord-45]
-	_ = x[actKillLine-46]
-	_ = x[actKillWord-47]
-	_ = x[actKillSubWord-48]
-	_ = x[actUnixLineDiscard-49]
-	_ = x[actUnixWordRubout-50]
-	_ = x[actYank-51]
-	_ = x[actBackwardKillWord-52]
-	_ = x[actBackwardKillSubWord-53]
-	_ = x[actSelectAll-54]
-	_ = x[actDeselectAll-55]
-	_ = x[actToggle-56]
-	_ = x[actToggleSearch-57]
-	_ = x[actToggleAll-58]
-	_ = x[actToggleDown-59]
-	_ = x[actToggleUp-60]
-	_ = x[actToggleIn-61]
-	_ = x[actToggleOut-62]
-	_ = x[actToggleTrack-63]
-	_ = x[actToggleTrackCurrent-64]
-	_ = x[actToggleHeader-65]
-	_ = x[actToggleWrap-66]
-	_ = x[actToggleWrapWord-67]
-	_ = x[actToggleMultiLine-68]
-	_ = x[actToggleHscroll-69]
-	_ = x[actToggleRaw-70]
-	_ = x[actEnableRaw-71]
-	_ = x[actDisableRaw-72]
-	_ = x[actTrackCurrent-73]
-	_ = x[actToggleInput-74]
-	_ = x[actHideInput-75]
-	_ = x[actShowInput-76]
-	_ = x[actUntrackCurrent-77]
-	_ = x[actDown-78]
-	_ = x[actDownMatch-79]
-	_ = x[actUp-80]
-	_ = x[actUpMatch-81]
-	_ = x[actPageUp-82]
-	_ = x[actPageDown-83]
-	_ = x[actPosition-84]
-	_ = x[actHalfPageUp-85]
-	_ = x[actHalfPageDown-86]
-	_ = x[actOffsetUp-87]
-	_ = x[actOffsetDown-88]
-	_ = x[actOffsetMiddle-89]
-	_ = x[actJump-90]
-	_ = x[actJumpAccept-91]
-	_ = x[actPrintQuery-92]
-	_ = x[actRefreshPreview-93]
-	_ = x[actReplaceQuery-94]
-	_ = x[actToggleSort-95]
-	_ = x[actShowPreview-96]
-	_ = x[actHidePreview-97]
-	_ = x[actTogglePreview-98]
-	_ = x[actTogglePreviewWrap-99]
-	_ = x[actTogglePreviewWrapWord-100]
-	_ = x[actTransform-101]
-	_ = x[actTransformBorderLabel-102]
-	_ = x[actTransformGhost-103]
-	_ = x[actTransformHeader-104]
-	_ = x[actTransformFooter-105]
-	_ = x[actTransformHeaderLabel-106]
-	_ = x[actTransformFooterLabel-107]
-	_ = x[actTransformInputLabel-108]
-	_ = x[actTransformListLabel-109]
-	_ = x[actTransformNth-110]
-	_ = x[actTransformPointer-111]
-	_ = x[actTransformPreviewLabel-112]
-	_ = x[actTransformPrompt-113]
-	_ = x[actTransformQuery-114]
-	_ = x[actTransformSearch-115]
-	_ = x[actTrigger-116]
-	_ = x[actBgTransform-117]
-	_ = x[actBgTransformBorderLabel-118]
-	_ = x[actBgTransformGhost-119]
-	_ = x[actBgTransformHeader-120]
-	_ = x[actBgTransformFooter-121]
-	_ = x[actBgTransformHeaderLabel-122]
-	_ = x[actBgTransformFooterLabel-123]
-	_ = x[actBgTransformInputLabel-124]
-	_ = x[actBgTransformListLabel-125]
-	_ = x[actBgTransformNth-126]
-	_ = x[actBgTransformPointer-127]
-	_ = x[actBgTransformPreviewLabel-128]
-	_ = x[actBgTransformPrompt-129]
-	_ = x[actBgTransformQuery-130]
-	_ = x[actBgTransformSearch-131]
-	_ = x[actBgCancel-132]
-	_ = x[actSearch-133]
-	_ = x[actPreview-134]
-	_ = x[actPreviewTop-135]
-	_ = x[actPreviewBottom-136]
-	_ = x[actPreviewUp-137]
-	_ = x[actPreviewDown-138]
-	_ = x[actPreviewPageUp-139]
-	_ = x[actPreviewPageDown-140]
-	_ = x[actPreviewHalfPageUp-141]
-	_ = x[actPreviewHalfPageDown-142]
-	_ = x[actPrevHistory-143]
-	_ = x[actPrevSelected-144]
-	_ = x[actPrint-145]
-	_ = x[actPut-146]
-	_ = x[actNextHistory-147]
-	_ = x[actNextSelected-148]
-	_ = x[actExecute-149]
-	_ = x[actExecuteSilent-150]
-	_ = x[actExecuteMulti-151]
-	_ = x[actSigStop-152]
-	_ = x[actBest-153]
-	_ = x[actFirst-154]
-	_ = x[actLast-155]
-	_ = x[actReload-156]
-	_ = x[actReloadSync-157]
-	_ = x[actDisableSearch-158]
-	_ = x[actEnableSearch-159]
-	_ = x[actSelect-160]
-	_ = x[actDeselect-161]
-	_ = x[actUnbind-162]
-	_ = x[actRebind-163]
-	_ = x[actToggleBind-164]
-	_ = x[actBecome-165]
-	_ = x[actShowHeader-166]
-	_ = x[actHideHeader-167]
-	_ = x[actBell-168]
-	_ = x[actExclude-169]
-	_ = x[actExcludeMulti-170]
-	_ = x[actAsync-171]
+	_ = x[actChangeHeaderLines-22]
+	_ = x[actChangeFooter-23]
+	_ = x[actChangeHeaderLabel-24]
+	_ = x[actChangeFooterLabel-25]
+	_ = x[actChangeInputLabel-26]
+	_ = x[actChangeListLabel-27]
+	_ = x[actChangeMulti-28]
+	_ = x[actChangeNth-29]
+	_ = x[actChangePointer-30]
+	_ = x[actChangePreview-31]
+	_ = x[actChangePreviewLabel-32]
+	_ = x[actChangePreviewWindow-33]
+	_ = x[actChangePrompt-34]
+	_ = x[actChangeQuery-35]
+	_ = x[actClearScreen-36]
+	_ = x[actClearQuery-37]
+	_ = x[actClearSelection-38]
+	_ = x[actClose-39]
+	_ = x[actDeleteChar-40]
+	_ = x[actDeleteCharEof-41]
+	_ = x[actEndOfLine-42]
+	_ = x[actFatal-43]
+	_ = x[actForwardChar-44]
+	_ = x[actForwardWord-45]
+	_ = x[actForwardSubWord-46]
+	_ = x[actKillLine-47]
+	_ = x[actKillWord-48]
+	_ = x[actKillSubWord-49]
+	_ = x[actUnixLineDiscard-50]
+	_ = x[actUnixWordRubout-51]
+	_ = x[actYank-52]
+	_ = x[actBackwardKillWord-53]
+	_ = x[actBackwardKillSubWord-54]
+	_ = x[actSelectAll-55]
+	_ = x[actDeselectAll-56]
+	_ = x[actToggle-57]
+	_ = x[actToggleSearch-58]
+	_ = x[actToggleAll-59]
+	_ = x[actToggleDown-60]
+	_ = x[actToggleUp-61]
+	_ = x[actToggleIn-62]
+	_ = x[actToggleOut-63]
+	_ = x[actToggleTrack-64]
+	_ = x[actToggleTrackCurrent-65]
+	_ = x[actToggleHeader-66]
+	_ = x[actToggleWrap-67]
+	_ = x[actToggleWrapWord-68]
+	_ = x[actToggleMultiLine-69]
+	_ = x[actToggleHscroll-70]
+	_ = x[actToggleRaw-71]
+	_ = x[actEnableRaw-72]
+	_ = x[actDisableRaw-73]
+	_ = x[actTrackCurrent-74]
+	_ = x[actToggleInput-75]
+	_ = x[actHideInput-76]
+	_ = x[actShowInput-77]
+	_ = x[actUntrackCurrent-78]
+	_ = x[actDown-79]
+	_ = x[actDownMatch-80]
+	_ = x[actUp-81]
+	_ = x[actUpMatch-82]
+	_ = x[actPageUp-83]
+	_ = x[actPageDown-84]
+	_ = x[actPosition-85]
+	_ = x[actHalfPageUp-86]
+	_ = x[actHalfPageDown-87]
+	_ = x[actOffsetUp-88]
+	_ = x[actOffsetDown-89]
+	_ = x[actOffsetMiddle-90]
+	_ = x[actJump-91]
+	_ = x[actJumpAccept-92]
+	_ = x[actPrintQuery-93]
+	_ = x[actRefreshPreview-94]
+	_ = x[actReplaceQuery-95]
+	_ = x[actToggleSort-96]
+	_ = x[actShowPreview-97]
+	_ = x[actHidePreview-98]
+	_ = x[actTogglePreview-99]
+	_ = x[actTogglePreviewWrap-100]
+	_ = x[actTogglePreviewWrapWord-101]
+	_ = x[actTransform-102]
+	_ = x[actTransformBorderLabel-103]
+	_ = x[actTransformGhost-104]
+	_ = x[actTransformHeader-105]
+	_ = x[actTransformHeaderLines-106]
+	_ = x[actTransformFooter-107]
+	_ = x[actTransformHeaderLabel-108]
+	_ = x[actTransformFooterLabel-109]
+	_ = x[actTransformInputLabel-110]
+	_ = x[actTransformListLabel-111]
+	_ = x[actTransformNth-112]
+	_ = x[actTransformPointer-113]
+	_ = x[actTransformPreviewLabel-114]
+	_ = x[actTransformPrompt-115]
+	_ = x[actTransformQuery-116]
+	_ = x[actTransformSearch-117]
+	_ = x[actTrigger-118]
+	_ = x[actBgTransform-119]
+	_ = x[actBgTransformBorderLabel-120]
+	_ = x[actBgTransformGhost-121]
+	_ = x[actBgTransformHeader-122]
+	_ = x[actBgTransformHeaderLines-123]
+	_ = x[actBgTransformFooter-124]
+	_ = x[actBgTransformHeaderLabel-125]
+	_ = x[actBgTransformFooterLabel-126]
+	_ = x[actBgTransformInputLabel-127]
+	_ = x[actBgTransformListLabel-128]
+	_ = x[actBgTransformNth-129]
+	_ = x[actBgTransformPointer-130]
+	_ = x[actBgTransformPreviewLabel-131]
+	_ = x[actBgTransformPrompt-132]
+	_ = x[actBgTransformQuery-133]
+	_ = x[actBgTransformSearch-134]
+	_ = x[actBgCancel-135]
+	_ = x[actSearch-136]
+	_ = x[actPreview-137]
+	_ = x[actPreviewTop-138]
+	_ = x[actPreviewBottom-139]
+	_ = x[actPreviewUp-140]
+	_ = x[actPreviewDown-141]
+	_ = x[actPreviewPageUp-142]
+	_ = x[actPreviewPageDown-143]
+	_ = x[actPreviewHalfPageUp-144]
+	_ = x[actPreviewHalfPageDown-145]
+	_ = x[actPrevHistory-146]
+	_ = x[actPrevSelected-147]
+	_ = x[actPrint-148]
+	_ = x[actPut-149]
+	_ = x[actNextHistory-150]
+	_ = x[actNextSelected-151]
+	_ = x[actExecute-152]
+	_ = x[actExecuteSilent-153]
+	_ = x[actExecuteMulti-154]
+	_ = x[actSigStop-155]
+	_ = x[actBest-156]
+	_ = x[actFirst-157]
+	_ = x[actLast-158]
+	_ = x[actReload-159]
+	_ = x[actReloadSync-160]
+	_ = x[actDisableSearch-161]
+	_ = x[actEnableSearch-162]
+	_ = x[actSelect-163]
+	_ = x[actDeselect-164]
+	_ = x[actUnbind-165]
+	_ = x[actRebind-166]
+	_ = x[actToggleBind-167]
+	_ = x[actBecome-168]
+	_ = x[actShowHeader-169]
+	_ = x[actHideHeader-170]
+	_ = x[actBell-171]
+	_ = x[actExclude-172]
+	_ = x[actExcludeMulti-173]
+	_ = x[actAsync-174]
 }
 
-const _actionType_name = "actIgnoreactStartactClickactInvalidactBracketedPasteBeginactBracketedPasteEndactCharactMouseactBeginningOfLineactAbortactAcceptactAcceptNonEmptyactAcceptOrPrintQueryactBackwardCharactBackwardDeleteCharactBackwardDeleteCharEofactBackwardWordactBackwardSubWordactCancelactChangeBorderLabelactChangeGhostactChangeHeaderactChangeFooteractChangeHeaderLabelactChangeFooterLabelactChangeInputLabelactChangeListLabelactChangeMultiactChangeNthactChangePointeractChangePreviewactChangePreviewLabelactChangePreviewWindowactChangePromptactChangeQueryactClearScreenactClearQueryactClearSelectionactCloseactDeleteCharactDeleteCharEofactEndOfLineactFatalactForwardCharactForwardWordactForwardSubWordactKillLineactKillWordactKillSubWordactUnixLineDiscardactUnixWordRuboutactYankactBackwardKillWordactBackwardKillSubWordactSelectAllactDeselectAllactToggleactToggleSearchactToggleAllactToggleDownactToggleUpactToggleInactToggleOutactToggleTrackactToggleTrackCurrentactToggleHeaderactToggleWrapactToggleWrapWordactToggleMultiLineactToggleHscrollactToggleRawactEnableRawactDisableRawactTrackCurrentactToggleInputactHideInputactShowInputactUntrackCurrentactDownactDownMatchactUpactUpMatchactPageUpactPageDownactPositionactHalfPageUpactHalfPageDownactOffsetUpactOffsetDownactOffsetMiddleactJumpactJumpAcceptactPrintQueryactRefreshPreviewactReplaceQueryactToggleSortactShowPreviewactHidePreviewactTogglePreviewactTogglePreviewWrapactTogglePreviewWrapWordactTransformactTransformBorderLabelactTransformGhostactTransformHeaderactTransformFooteractTransformHeaderLabelactTransformFooterLabelactTransformInputLabelactTransformListLabelactTransformNthactTransformPointeractTransformPreviewLabelactTransformPromptactTransformQueryactTransformSearchactTriggeractBgTransformactBgTransformBorderLabelactBgTransformGhostactBgTransformHeaderactBgTransformFooteractBgTransformHeaderLabelactBgTransformFooterLabelactBgTransformInputLabelactBgTransformListLabelactBgTransformNthactBgTransformPointeractBgTransformPreviewLabelactBgTransformPromptactBgTransformQueryactBgTransformSearchactBgCancelactSearchactPreviewactPreviewTopactPreviewBottomactPreviewUpactPreviewDownactPreviewPageUpactPreviewPageDownactPreviewHalfPageUpactPreviewHalfPageDownactPrevHistoryactPrevSelectedactPrintactPutactNextHistoryactNextSelectedactExecuteactExecuteSilentactExecuteMultiactSigStopactBestactFirstactLastactReloadactReloadSyncactDisableSearchactEnableSearchactSelectactDeselectactUnbindactRebindactToggleBindactBecomeactShowHeaderactHideHeaderactBellactExcludeactExcludeMultiactAsync"
+const _actionType_name = "actIgnoreactStartactClickactInvalidactBracketedPasteBeginactBracketedPasteEndactCharactMouseactBeginningOfLineactAbortactAcceptactAcceptNonEmptyactAcceptOrPrintQueryactBackwardCharactBackwardDeleteCharactBackwardDeleteCharEofactBackwardWordactBackwardSubWordactCancelactChangeBorderLabelactChangeGhostactChangeHeaderactChangeHeaderLinesactChangeFooteractChangeHeaderLabelactChangeFooterLabelactChangeInputLabelactChangeListLabelactChangeMultiactChangeNthactChangePointeractChangePreviewactChangePreviewLabelactChangePreviewWindowactChangePromptactChangeQueryactClearScreenactClearQueryactClearSelectionactCloseactDeleteCharactDeleteCharEofactEndOfLineactFatalactForwardCharactForwardWordactForwardSubWordactKillLineactKillWordactKillSubWordactUnixLineDiscardactUnixWordRuboutactYankactBackwardKillWordactBackwardKillSubWordactSelectAllactDeselectAllactToggleactToggleSearchactToggleAllactToggleDownactToggleUpactToggleInactToggleOutactToggleTrackactToggleTrackCurrentactToggleHeaderactToggleWrapactToggleWrapWordactToggleMultiLineactToggleHscrollactToggleRawactEnableRawactDisableRawactTrackCurrentactToggleInputactHideInputactShowInputactUntrackCurrentactDownactDownMatchactUpactUpMatchactPageUpactPageDownactPositionactHalfPageUpactHalfPageDownactOffsetUpactOffsetDownactOffsetMiddleactJumpactJumpAcceptactPrintQueryactRefreshPreviewactReplaceQueryactToggleSortactShowPreviewactHidePreviewactTogglePreviewactTogglePreviewWrapactTogglePreviewWrapWordactTransformactTransformBorderLabelactTransformGhostactTransformHeaderactTransformHeaderLinesactTransformFooteractTransformHeaderLabelactTransformFooterLabelactTransformInputLabelactTransformListLabelactTransformNthactTransformPointeractTransformPreviewLabelactTransformPromptactTransformQueryactTransformSearchactTriggeractBgTransformactBgTransformBorderLabelactBgTransformGhostactBgTransformHeaderactBgTransformHeaderLinesactBgTransformFooteractBgTransformHeaderLabelactBgTransformFooterLabelactBgTransformInputLabelactBgTransformListLabelactBgTransformNthactBgTransformPointeractBgTransformPreviewLabelactBgTransformPromptactBgTransformQueryactBgTransformSearchactBgCancelactSearchactPreviewactPreviewTopactPreviewBottomactPreviewUpactPreviewDownactPreviewPageUpactPreviewPageDownactPreviewHalfPageUpactPreviewHalfPageDownactPrevHistoryactPrevSelectedactPrintactPutactNextHistoryactNextSelectedactExecuteactExecuteSilentactExecuteMultiactSigStopactBestactFirstactLastactReloadactReloadSyncactDisableSearchactEnableSearchactSelectactDeselectactUnbindactRebindactToggleBindactBecomeactShowHeaderactHideHeaderactBellactExcludeactExcludeMultiactAsync"
 
-var _actionType_index = [...]uint16{0, 9, 17, 25, 35, 57, 77, 84, 92, 110, 118, 127, 144, 165, 180, 201, 225, 240, 258, 267, 287, 301, 316, 331, 351, 371, 390, 408, 422, 434, 450, 466, 487, 509, 524, 538, 552, 565, 582, 590, 603, 619, 631, 639, 653, 667, 684, 695, 706, 720, 738, 755, 762, 781, 803, 815, 829, 838, 853, 865, 878, 889, 900, 912, 926, 947, 962, 975, 992, 1010, 1026, 1038, 1050, 1063, 1078, 1092, 1104, 1116, 1133, 1140, 1152, 1157, 1167, 1176, 1187, 1198, 1211, 1226, 1237, 1250, 1265, 1272, 1285, 1298, 1315, 1330, 1343, 1357, 1371, 1387, 1407, 1431, 1443, 1466, 1483, 1501, 1519, 1542, 1565, 1587, 1608, 1623, 1642, 1666, 1684, 1701, 1719, 1729, 1743, 1768, 1787, 1807, 1827, 1852, 1877, 1901, 1924, 1941, 1962, 1988, 2008, 2027, 2047, 2058, 2067, 2077, 2090, 2106, 2118, 2132, 2148, 2166, 2186, 2208, 2222, 2237, 2245, 2251, 2265, 2280, 2290, 2306, 2321, 2331, 2338, 2346, 2353, 2362, 2375, 2391, 2406, 2415, 2426, 2435, 2444, 2457, 2466, 2479, 2492, 2499, 2509, 2524, 2532}
+var _actionType_index = [...]uint16{0, 9, 17, 25, 35, 57, 77, 84, 92, 110, 118, 127, 144, 165, 180, 201, 225, 240, 258, 267, 287, 301, 316, 336, 351, 371, 391, 410, 428, 442, 454, 470, 486, 507, 529, 544, 558, 572, 585, 602, 610, 623, 639, 651, 659, 673, 687, 704, 715, 726, 740, 758, 775, 782, 801, 823, 835, 849, 858, 873, 885, 898, 909, 920, 932, 946, 967, 982, 995, 1012, 1030, 1046, 1058, 1070, 1083, 1098, 1112, 1124, 1136, 1153, 1160, 1172, 1177, 1187, 1196, 1207, 1218, 1231, 1246, 1257, 1270, 1285, 1292, 1305, 1318, 1335, 1350, 1363, 1377, 1391, 1407, 1427, 1451, 1463, 1486, 1503, 1521, 1544, 1562, 1585, 1608, 1630, 1651, 1666, 1685, 1709, 1727, 1744, 1762, 1772, 1786, 1811, 1830, 1850, 1875, 1895, 1920, 1945, 1969, 1992, 2009, 2030, 2056, 2076, 2095, 2115, 2126, 2135, 2145, 2158, 2174, 2186, 2200, 2216, 2234, 2254, 2276, 2290, 2305, 2313, 2319, 2333, 2348, 2358, 2374, 2389, 2399, 2406, 2414, 2421, 2430, 2443, 2459, 2474, 2483, 2494, 2503, 2512, 2525, 2534, 2547, 2560, 2567, 2577, 2592, 2600}
 
 func (i actionType) String() string {
 	if i < 0 || i >= actionType(len(_actionType_index)-1) {

src/chunklist.go

@@ -52,6 +52,20 @@ func (cl *ChunkList) lastChunk() *Chunk {
 	return cl.chunks[len(cl.chunks)-1]
 }
 
+// GetItems returns the first n items from the given chunks
+func GetItems(chunks []*Chunk, n int) []Item {
+	items := make([]Item, 0, n)
+	for _, chunk := range chunks {
+		for i := 0; i < chunk.count && len(items) < n; i++ {
+			items = append(items, chunk.items[i])
+		}
+		if len(items) >= n {
+			break
+		}
+	}
+	return items
+}
+
 // CountItems returns the total number of Items
 func CountItems(cs []*Chunk) int {
 	if len(cs) == 0 {

src/constants.go

@@ -65,7 +65,6 @@ const (
 	EvtSearchNew
 	EvtSearchProgress
 	EvtSearchFin
-	EvtHeader
 	EvtReady
 	EvtQuit
 )

src/core.go

@@ -17,7 +17,6 @@ Reader   -> EvtReadNew        -> Matcher  (restart)
 Terminal -> EvtSearchNew:bool -> Matcher  (restart)
 Matcher  -> EvtSearchProgress -> Terminal (update info)
 Matcher  -> EvtSearchFin      -> Terminal (update list)
-Matcher  -> EvtHeader         -> Terminal (update header)
 */
 
 type revision struct {
@@ -113,14 +112,8 @@ func Run(opts *Options) (int, error) {
 	cache := NewChunkCache()
 	var chunkList *ChunkList
 	var itemIndex int32
-	header := make([]string, 0, opts.HeaderLines)
 	if opts.WithNth == nil {
 		chunkList = NewChunkList(cache, func(item *Item, data []byte) bool {
-			if len(header) < opts.HeaderLines {
-				header = append(header, byteString(data))
-				eventBox.Set(EvtHeader, header)
-				return false
-			}
 			item.text, item.colors = ansiProcessor(data)
 			item.text.Index = itemIndex
 			itemIndex++
@@ -147,11 +140,6 @@ func Run(opts *Options) (int, error) {
 				}
 			}
 			transformed := nthTransformer(tokens, itemIndex)
-			if len(header) < opts.HeaderLines {
-				header = append(header, transformed)
-				eventBox.Set(EvtHeader, header)
-				return false
-			}
 			item.text, item.colors = ansiProcessor(stringBytes(transformed))
 
 			// We should not trim trailing whitespaces with background colors
@@ -236,13 +224,15 @@ func Run(opts *Options) (int, error) {
 		denylist = make(map[int32]struct{})
 		denyMutex.Unlock()
 	}
+	headerLines := int32(opts.HeaderLines)
+	headerUpdated := false
 	patternBuilder := func(runes []rune) *Pattern {
 		denyMutex.Lock()
 		denylistCopy := maps.Clone(denylist)
 		denyMutex.Unlock()
 		return BuildPattern(cache, patternCache,
 			opts.Fuzzy, opts.FuzzyAlgo, opts.Extended, opts.Case, opts.Normalize, forward, withPos,
-			opts.Filter == nil, nth, opts.Delimiter, inputRevision, runes, denylistCopy)
+			opts.Filter == nil, nth, opts.Delimiter, inputRevision, runes, denylistCopy, headerLines)
 	}
 	matcher := NewMatcher(cache, patternBuilder, sort, opts.Tac, eventBox, inputRevision)
 
@@ -265,6 +255,9 @@ func Run(opts *Options) (int, error) {
 				func(runes []byte) bool {
 					item := Item{}
 					if chunkList.trans(&item, runes) {
+						if item.Index() < headerLines {
+							return false
+						}
 						mutex.Lock()
 						if result, _, _ := pattern.MatchItem(&item, false, slab); result != nil {
 							opts.Printer(transformer(&item))
@@ -349,11 +342,11 @@ func Run(opts *Options) (int, error) {
 			clearDenylist()
 		}
 		reading = true
+		headerUpdated = false
 		startTick = ticks
 		chunkList.Clear()
 		itemIndex = 0
 		inputRevision.bumpMajor()
-		header = make([]string, 0, opts.HeaderLines)
 		readyChan := make(chan bool)
 		go reader.restart(command, environ, readyChan)
 		<-readyChan
@@ -411,7 +404,11 @@ func Run(opts *Options) (int, error) {
 						snapshotRevision = inputRevision
 					}
 					total = count
-					terminal.UpdateCount(total, !reading, value.(*string))
+					terminal.UpdateCount(max(0, total-int(headerLines)), !reading, value.(*string))
+					if headerLines > 0 && !headerUpdated {
+						terminal.UpdateHeader(GetItems(snapshot, int(headerLines)))
+						headerUpdated = int32(total) >= headerLines
+					}
 					if heightUnknown && !deferred {
 						determine(!reading)
 					}
@@ -421,6 +418,7 @@ func Run(opts *Options) (int, error) {
 					var command *commandSpec
 					var environ []string
 					var changed bool
+					headerLinesChanged := false
 					switch val := value.(type) {
 					case searchRequest:
 						sort = val.sort
@@ -441,6 +439,12 @@ func Run(opts *Options) (int, error) {
 							nth = *val.nth
 							bump = true
 						}
+						if val.headerLines != nil {
+							headerLines = int32(*val.headerLines)
+							headerUpdated = false
+							headerLinesChanged = true
+							bump = true
+						}
 						if bump {
 							patternCache = make(map[string]*Pattern)
 							cache.Clear()
@@ -477,6 +481,14 @@ func Run(opts *Options) (int, error) {
 							snapshotRevision = inputRevision
 						}
 					}
+					if headerLinesChanged {
+						terminal.UpdateCount(max(0, total-int(headerLines)), !reading, nil)
+						if headerLines > 0 {
+							terminal.UpdateHeader(GetItems(snapshot, int(headerLines)))
+						} else {
+							terminal.UpdateHeader(nil)
+						}
+					}
 					matcher.Reset(snapshot, input(), true, !reading, sort, snapshotRevision)
 					delay = false
 
@@ -486,11 +498,6 @@ func Run(opts *Options) (int, error) {
 						terminal.UpdateProgress(val)
 					}
 
-				case EvtHeader:
-					headerPadded := make([]string, opts.HeaderLines)
-					copy(headerPadded, value.([]string))
-					terminal.UpdateHeader(headerPadded)
-
 				case EvtSearchFin:
 					switch val := value.(type) {
 					case MatchResult:

src/matcher.go

@@ -174,7 +174,7 @@ func (m *Matcher) scan(request MatchRequest) MatchResult {
 		return MatchResult{m, m, false}
 	}
 	pattern := request.pattern
-	passMerger := PassMerger(&request.chunks, m.tac, request.revision)
+	passMerger := PassMerger(&request.chunks, m.tac, request.revision, pattern.startIndex)
 	if pattern.IsEmpty() {
 		return MatchResult{passMerger, passMerger, false}
 	}

src/merger.go

@@ -10,42 +10,46 @@ func EmptyMerger(revision revision) *Merger {
 // Merger holds a set of locally sorted lists of items and provides the view of
 // a single, globally-sorted list
 type Merger struct {
-	pattern  *Pattern
-	lists    [][]Result
-	merged   []Result
-	chunks   *[]*Chunk
-	cursors  []int
-	sorted   bool
-	tac      bool
-	final    bool
-	count    int
-	pass     bool
-	revision revision
-	minIndex int32
-	maxIndex int32
+	pattern    *Pattern
+	lists      [][]Result
+	merged     []Result
+	chunks     *[]*Chunk
+	cursors    []int
+	sorted     bool
+	tac        bool
+	final      bool
+	count      int
+	pass       bool
+	startIndex int
+	revision   revision
+	minIndex   int32
+	maxIndex   int32
 }
 
 // PassMerger returns a new Merger that simply returns the items in the
-// original order
-func PassMerger(chunks *[]*Chunk, tac bool, revision revision) *Merger {
+// original order. startIndex items are skipped from the beginning.
+func PassMerger(chunks *[]*Chunk, tac bool, revision revision, startIndex int32) *Merger {
 	var minIndex, maxIndex int32
 	if len(*chunks) > 0 {
 		minIndex = (*chunks)[0].items[0].Index()
 		maxIndex = (*chunks)[len(*chunks)-1].lastIndex(minIndex)
 	}
+	si := int(startIndex)
 	mg := Merger{
-		pattern:  nil,
-		chunks:   chunks,
-		tac:      tac,
-		count:    0,
-		pass:     true,
-		revision: revision,
-		minIndex: minIndex,
-		maxIndex: maxIndex}
+		pattern:    nil,
+		chunks:     chunks,
+		tac:        tac,
+		count:      0,
+		pass:       true,
+		startIndex: si,
+		revision:   revision,
+		minIndex:   minIndex + startIndex,
+		maxIndex:   maxIndex}
 
 	for _, chunk := range *mg.chunks {
 		mg.count += chunk.count
 	}
+	mg.count = max(0, mg.count-si)
 	return &mg
 }
 
@@ -113,6 +117,7 @@ func (mg *Merger) Get(idx int) Result {
 		if mg.tac {
 			idx = mg.count - idx - 1
 		}
+		idx += mg.startIndex
 		firstChunk := (*mg.chunks)[0]
 		if firstChunk.count < chunkSize && idx >= firstChunk.count {
 			idx -= firstChunk.count

src/options.go

@@ -1626,7 +1626,7 @@ const (
 
 func init() {
 	executeRegexp = regexp.MustCompile(
-		`(?si)[:+](become|execute(?:-multi|-silent)?|reload(?:-sync)?|preview|(?:change|bg-transform|transform)-(?:query|prompt|(?:border|list|preview|input|header|footer)-label|header|footer|search|nth|pointer|ghost)|bg-transform|transform|change-(?:preview-window|preview|multi)|(?:re|un|toggle-)bind|pos|put|print|search|trigger)`)
+		`(?si)[:+](become|execute(?:-multi|-silent)?|reload(?:-sync)?|preview|(?:change|bg-transform|transform)-(?:query|prompt|(?:border|list|preview|input|header|footer)-label|header-lines|header|footer|search|nth|pointer|ghost)|bg-transform|transform|change-(?:preview-window|preview|multi)|(?:re|un|toggle-)bind|pos|put|print|search|trigger)`)
 	splitRegexp = regexp.MustCompile("[,:]+")
 	actionNameRegexp = regexp.MustCompile("(?i)^[a-z-]+")
 }
@@ -2037,6 +2037,8 @@ func isExecuteAction(str string) actionType {
 		return actPreview
 	case "change-header":
 		return actChangeHeader
+	case "change-header-lines":
+		return actChangeHeaderLines
 	case "change-footer":
 		return actChangeFooter
 	case "change-list-label":
@@ -2097,6 +2099,8 @@ func isExecuteAction(str string) actionType {
 		return actTransformFooter
 	case "transform-header":
 		return actTransformHeader
+	case "transform-header-lines":
+		return actTransformHeaderLines
 	case "transform-ghost":
 		return actTransformGhost
 	case "transform-nth":
@@ -2127,6 +2131,8 @@ func isExecuteAction(str string) actionType {
 		return actBgTransformFooter
 	case "bg-transform-header":
 		return actBgTransformHeader
+	case "bg-transform-header-lines":
+		return actBgTransformHeaderLines
 	case "bg-transform-ghost":
 		return actBgTransformGhost
 	case "bg-transform-nth":

src/pattern.go

@@ -64,6 +64,7 @@ type Pattern struct {
 	procFun       map[termType]algo.Algo
 	cache         *ChunkCache
 	denylist      map[int32]struct{}
+	startIndex    int32
 }
 
 var _splitRegex *regexp.Regexp
@@ -74,7 +75,7 @@ func init() {
 
 // BuildPattern builds Pattern object from the given arguments
 func BuildPattern(cache *ChunkCache, patternCache map[string]*Pattern, fuzzy bool, fuzzyAlgo algo.Algo, extended bool, caseMode Case, normalize bool, forward bool,
-	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, revision revision, runes []rune, denylist map[int32]struct{}) *Pattern {
+	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, revision revision, runes []rune, denylist map[int32]struct{}, startIndex int32) *Pattern {
 
 	var asString string
 	if extended {
@@ -146,6 +147,7 @@ func BuildPattern(cache *ChunkCache, patternCache map[string]*Pattern, fuzzy boo
 		delimiter:     delimiter,
 		cache:         cache,
 		denylist:      denylist,
+		startIndex:    startIndex,
 		procFun:       make(map[termType]algo.Algo)}
 
 	ptr.cacheKey = ptr.buildCacheKey()
@@ -301,10 +303,19 @@ func (p *Pattern) Match(chunk *Chunk, slab *util.Slab) []Result {
 func (p *Pattern) matchChunk(chunk *Chunk, space []Result, slab *util.Slab) []Result {
 	matches := []Result{}
 
+	// Skip header items in chunks that contain them
+	startIdx := 0
+	if p.startIndex > 0 && chunk.count > 0 && chunk.items[0].Index() < p.startIndex {
+		startIdx = int(p.startIndex - chunk.items[0].Index())
+		if startIdx >= chunk.count {
+			return matches
+		}
+	}
+
 	if len(p.denylist) == 0 {
 		// Huge code duplication for minimizing unnecessary map lookups
 		if space == nil {
-			for idx := 0; idx < chunk.count; idx++ {
+			for idx := startIdx; idx < chunk.count; idx++ {
 				if match, _, _ := p.MatchItem(&chunk.items[idx], p.withPos, slab); match != nil {
 					matches = append(matches, *match)
 				}
@@ -320,7 +331,7 @@ func (p *Pattern) matchChunk(chunk *Chunk, space []Result, slab *util.Slab) []Re
 	}
 
 	if space == nil {
-		for idx := 0; idx < chunk.count; idx++ {
+		for idx := startIdx; idx < chunk.count; idx++ {
 			if _, prs := p.denylist[chunk.items[idx].Index()]; prs {
 				continue
 			}

src/pattern_test.go

@@ -68,7 +68,7 @@ func buildPattern(fuzzy bool, fuzzyAlgo algo.Algo, extended bool, caseMode Case,
 	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, runes []rune) *Pattern {
 	return BuildPattern(NewChunkCache(), make(map[string]*Pattern),
 		fuzzy, fuzzyAlgo, extended, caseMode, normalize, forward,
-		withPos, cacheable, nth, delimiter, revision{}, runes, nil)
+		withPos, cacheable, nth, delimiter, revision{}, runes, nil, 0)
 }
 
 func TestExact(t *testing.T) {

src/terminal.go

@@ -314,6 +314,7 @@ type Terminal struct {
 	sort                 bool
 	toggleSort           bool
 	track                trackOption
+	targetIndex          int32
 	delimiter            Delimiter
 	expect               map[tui.Event]string
 	keymap               map[tui.Event][]*action
@@ -327,7 +328,7 @@ type Terminal struct {
 	headerVisible        bool
 	headerFirst          bool
 	headerLines          int
-	header               []string
+	header               []Item
 	header0              []string
 	footer               []string
 	ellipsis             string
@@ -542,6 +543,7 @@ const (
 	actChangeBorderLabel
 	actChangeGhost
 	actChangeHeader
+	actChangeHeaderLines
 	actChangeFooter
 	actChangeHeaderLabel
 	actChangeFooterLabel
@@ -627,6 +629,7 @@ const (
 	actTransformBorderLabel
 	actTransformGhost
 	actTransformHeader
+	actTransformHeaderLines
 	actTransformFooter
 	actTransformHeaderLabel
 	actTransformFooterLabel
@@ -645,6 +648,7 @@ const (
 	actBgTransformBorderLabel
 	actBgTransformGhost
 	actBgTransformHeader
+	actBgTransformHeaderLines
 	actBgTransformFooter
 	actBgTransformHeaderLabel
 	actBgTransformFooterLabel
@@ -710,6 +714,7 @@ func processExecution(action actionType) bool {
 		actTransformBorderLabel,
 		actTransformGhost,
 		actTransformHeader,
+		actTransformHeaderLines,
 		actTransformFooter,
 		actTransformHeaderLabel,
 		actTransformFooterLabel,
@@ -725,6 +730,7 @@ func processExecution(action actionType) bool {
 		actBgTransformBorderLabel,
 		actBgTransformGhost,
 		actBgTransformHeader,
+		actBgTransformHeaderLines,
 		actBgTransformFooter,
 		actBgTransformHeaderLabel,
 		actBgTransformFooterLabel,
@@ -761,14 +767,15 @@ type placeholderFlags struct {
 }
 
 type searchRequest struct {
-	sort     bool
-	sync     bool
-	nth      *[]Range
-	command  *commandSpec
-	environ  []string
-	changed  bool
-	denylist []int32
-	revision revision
+	sort        bool
+	sync        bool
+	nth         *[]Range
+	headerLines *int
+	command     *commandSpec
+	environ     []string
+	changed     bool
+	denylist    []int32
+	revision    revision
 }
 
 type previewRequest struct {
@@ -1022,6 +1029,7 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		sort:               opts.Sort > 0,
 		toggleSort:         opts.ToggleSort,
 		track:              opts.Track,
+		targetIndex:        minItem.Index(),
 		delimiter:          opts.Delimiter,
 		expect:             opts.Expect,
 		keymap:             opts.Keymap,
@@ -1063,7 +1071,7 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		headerFirst:        opts.HeaderFirst,
 		headerLines:        opts.HeaderLines,
 		gap:                opts.Gap,
-		header:             []string{},
+		header:             []Item{},
 		footer:             opts.Footer,
 		header0:            opts.Header,
 		ansi:               opts.Ansi,
@@ -1364,7 +1372,7 @@ func (t *Terminal) environImpl(forPreview bool) []string {
 		}
 	}
 	env = append(env, "FZF_INPUT_STATE="+inputState)
-	env = append(env, fmt.Sprintf("FZF_TOTAL_COUNT=%d", t.count))
+	env = append(env, fmt.Sprintf("FZF_TOTAL_COUNT=%d", max(0, t.count-t.headerLines)))
 	env = append(env, fmt.Sprintf("FZF_MATCH_COUNT=%d", t.resultMerger.Length()))
 	env = append(env, fmt.Sprintf("FZF_SELECT_COUNT=%d", len(t.selected)))
 	env = append(env, fmt.Sprintf("FZF_LINES=%d", t.areaLines))
@@ -1755,8 +1763,14 @@ func (t *Terminal) changeFooter(footer string) {
 }
 
 // UpdateHeader updates the header
-func (t *Terminal) UpdateHeader(header []string) {
+func (t *Terminal) UpdateHeader(header []Item) {
 	t.mutex.Lock()
+	// Pad to t.headerLines so that click coordinate mapping works correctly
+	if len(header) < t.headerLines {
+		padded := make([]Item, t.headerLines)
+		copy(padded, header)
+		header = padded
+	}
 	t.header = header
 	t.mutex.Unlock()
 	t.reqBox.Set(reqHeader, nil)
@@ -1788,6 +1802,10 @@ func (t *Terminal) UpdateList(result MatchResult) {
 			prevIndex = merger.First().item.Index()
 		}
 	}
+	if t.targetIndex != minItem.Index() {
+		prevIndex = t.targetIndex
+		t.targetIndex = minItem.Index()
+	}
 	t.progress = 100
 	t.merger = merger
 	t.resultMerger = merger
@@ -3079,11 +3097,11 @@ func (t *Terminal) printHeader() {
 	}
 
 	t.withWindow(t.headerWindow, func() {
-		var lines []string
+		var headerItems []Item
 		if !t.hasHeaderLinesWindow() {
-			lines = t.header
+			headerItems = t.header
 		}
-		t.printHeaderImpl(t.headerWindow, t.headerBorderShape, t.header0, lines)
+		t.printHeaderImpl(t.headerWindow, t.headerBorderShape, t.header0, headerItems)
 	})
 	if w, shape := t.determineHeaderLinesShape(); w {
 		t.withWindow(t.headerLinesWindow, func() {
@@ -3145,7 +3163,7 @@ func (t *Terminal) headerIndentImpl(base int, borderShape tui.BorderShape) int {
 	return indentSize
 }
 
-func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShape, lines1 []string, lines2 []string) {
+func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShape, lines1 []string, lines2 []Item) {
 	max := t.window.Height()
 	if !t.inputless && t.inputWindow == nil && window == nil && t.headerFirst {
 		max--
@@ -3172,7 +3190,8 @@ func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShap
 	}
 	indent := strings.Repeat(" ", indentSize)
 	t.wrap = false
-	for idx, lineStr := range append(append([]string{}, lines1...), lines2...) {
+	totalLines := len(lines1) + len(lines2)
+	for idx := 0; idx < totalLines; idx++ {
 		line := idx
 		if needReverse && idx < len(lines1) {
 			line = len(lines1) - idx - 1
@@ -3186,11 +3205,18 @@ func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShap
 		if line >= max {
 			continue
 		}
-		trimmed, colors, newState := extractColor(lineStr, state, nil)
-		state = newState
-		item := &Item{
-			text:   util.ToChars([]byte(trimmed)),
-			colors: colors}
+
+		var item *Item
+		if idx < len(lines1) {
+			trimmed, colors, newState := extractColor(lines1[idx], state, nil)
+			state = newState
+			item = &Item{
+				text:   util.ToChars([]byte(trimmed)),
+				colors: colors}
+		} else {
+			headerItem := lines2[idx-len(lines1)]
+			item = &headerItem
+		}
 
 		t.printHighlighted(Result{item: item},
 			tui.ColHeader, tui.ColHeader, false, false, false, line, line, true,
@@ -5288,9 +5314,13 @@ func (t *Terminal) addClickHeaderWord(env []string) []string {
 		return env
 	}
 
-	// NOTE: t.header is padded with empty strings so that its size is equal to t.headerLines
 	nthBase := 0
-	headers := [2][]string{t.header, t.header0}
+	// Convert header items to strings for click handling
+	headerStrs := make([]string, len(t.header))
+	for i, item := range t.header {
+		headerStrs[i] = item.text.ToString()
+	}
+	headers := [2][]string{headerStrs, t.header0}
 	if t.layout == layoutReverse {
 		headers[0], headers[1] = headers[1], headers[0]
 	}
@@ -5892,6 +5922,7 @@ func (t *Terminal) Loop() error {
 	events := []util.EventType{}
 	changed := false
 	var newNth *[]Range
+	var newHeaderLines *int
 	req := func(evts ...util.EventType) {
 		for _, event := range evts {
 			events = append(events, event)
@@ -5908,6 +5939,7 @@ func (t *Terminal) Loop() error {
 		events = []util.EventType{}
 		changed = false
 		newNth = nil
+		newHeaderLines = nil
 		beof := false
 		queryChanged := false
 		denylist := []int32{}
@@ -6247,6 +6279,23 @@ func (t *Terminal) Loop() error {
 				}
 			case actPrintQuery:
 				req(reqPrintQuery)
+			case actChangeHeaderLines, actTransformHeaderLines, actBgTransformHeaderLines:
+				capture(true, func(expr string) {
+					if n, err := strconv.Atoi(expr); err == nil && n >= 0 && n != t.headerLines {
+						t.headerLines = n
+						newHeaderLines = &n
+						changed = true
+						// Deselect items that are now part of the header
+						for idx := range t.selected {
+							if idx < int32(n) {
+								delete(t.selected, idx)
+							}
+						}
+						// Tell UpdateList to reposition cursor to the current item
+						t.targetIndex = t.currentIndex()
+						req(reqList, reqPrompt, reqInfo, reqHeader)
+					}
+				})
 			case actChangeMulti:
 				multi := t.multi
 				if a.a == "" {
@@ -7428,7 +7477,7 @@ func (t *Terminal) Loop() error {
 		reload := changed || newCommand != nil
 		var reloadRequest *searchRequest
 		if reload {
-			reloadRequest = &searchRequest{sort: t.sort, sync: reloadSync, nth: newNth, command: newCommand, environ: t.environ(), changed: changed, denylist: denylist, revision: t.resultMerger.Revision()}
+			reloadRequest = &searchRequest{sort: t.sort, sync: reloadSync, nth: newNth, headerLines: newHeaderLines, command: newCommand, environ: t.environ(), changed: changed, denylist: denylist, revision: t.resultMerger.Revision()}
 		}
 
 		// Dispatch queued background requests