Add environment variables: FZF_{BORDER,PREVIEW}_LABEL (#3693)

The environment variable get the value of the preview label, even if it
has been updated with an action. It can be useful to track the label of
the preview and be able to switch between previews using only one
binding.

Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>

4 files changed, 44 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cc1e8fa1..c90242fb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,17 @@ CHANGELOG
 
 0.49.0
 ------
+- Added two environment variables exported to the child processes
+    - `FZF_PREVIEW_LABEL`
+    - `FZF_BORDER_LABEL`
+    ```sh
+    # Use the current value of $FZF_PREVIEW_LABEL to determine which actions to perform
+    git ls-files |
+      fzf --header 'Press CTRL-P to change preview mode' \
+          --bind='ctrl-p:transform:[[ $FZF_PREVIEW_LABEL =~ cat ]] \
+          && echo "change-preview(git log --color=always \{})+change-preview-label([[ log ]])" \
+          || echo "change-preview(bat --color=always \{})+change-preview-label([[ cat ]])"'
+    ```
 - Renamed `track` action to `track-current` to highlight the difference between the global tracking state set by `--track` and a one-off tracking action
     - `track` is still available as an alias
 - Added `untrack-current` and `toggle-track-current` actions
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index a02b45c1..3f8619ab 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -975,6 +975,10 @@ fzf exports the following environment variables to its child processes.
 .br
 .BR FZF_PROMPT "          Prompt string"
 .br
+.BR FZF_PREVIEW_LABEL "   Preview label string"
+.br
+.BR FZF_BORDER_LABEL "    Border label string"
+.br
 .BR FZF_ACTION "          The name of the last action performed"
 .br
 .BR FZF_PORT "            Port number when --listen option is used"
diff --git a/src/terminal.go b/src/terminal.go
index 726cb498..ef7ba9dd 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -852,6 +852,8 @@ func (t *Terminal) environ() []string {
 	env = append(env, "FZF_QUERY="+string(t.input))
 	env = append(env, "FZF_ACTION="+t.lastAction.Name())
 	env = append(env, "FZF_PROMPT="+string(t.promptString))
+	env = append(env, "FZF_PREVIEW_LABEL="+t.previewLabelOpts.label)
+	env = append(env, "FZF_BORDER_LABEL="+t.borderLabelOpts.label)
 	env = append(env, fmt.Sprintf("FZF_TOTAL_COUNT=%d", t.count))
 	env = append(env, fmt.Sprintf("FZF_MATCH_COUNT=%d", t.merger.Length()))
 	env = append(env, fmt.Sprintf("FZF_SELECT_COUNT=%d", len(t.selected)))
@@ -3476,11 +3478,13 @@ func (t *Terminal) Loop() {
 					req(reqHeader)
 				}
 			case actChangeBorderLabel:
+				t.borderLabelOpts.label = a.a
 				if t.border != nil {
 					t.borderLabel, t.borderLabelLen = t.ansiLabelPrinter(a.a, &tui.ColBorderLabel, false)
 					req(reqRedrawBorderLabel)
 				}
 			case actChangePreviewLabel:
+				t.previewLabelOpts.label = a.a
 				if t.pborder != nil {
 					t.previewLabel, t.previewLabelLen = t.ansiLabelPrinter(a.a, &tui.ColPreviewLabel, false)
 					req(reqRedrawPreviewLabel)
@@ -3490,14 +3494,16 @@ func (t *Terminal) Loop() {
 				actions := parseSingleActionList(strings.Trim(body, "\r\n"), func(message string) {})
 				return doActions(actions)
 			case actTransformBorderLabel:
+				label := t.executeCommand(a.a, false, true, true, true)
+				t.borderLabelOpts.label = label
 				if t.border != nil {
-					label := t.executeCommand(a.a, false, true, true, true)
 					t.borderLabel, t.borderLabelLen = t.ansiLabelPrinter(label, &tui.ColBorderLabel, false)
 					req(reqRedrawBorderLabel)
 				}
 			case actTransformPreviewLabel:
+				label := t.executeCommand(a.a, false, true, true, true)
+				t.previewLabelOpts.label = label
 				if t.pborder != nil {
-					label := t.executeCommand(a.a, false, true, true, true)
 					t.previewLabel, t.previewLabelLen = t.ansiLabelPrinter(label, &tui.ColPreviewLabel, false)
 					req(reqRedrawPreviewLabel)
 				}
diff --git a/test/test_go.rb b/test/test_go.rb
index f44f6379..e4d365e9 100755
--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -2877,6 +2877,27 @@ class TestGoFZF < TestBase
     end
   end
 
+  def test_labels_variables
+    tmux.send_keys ': | fzf --border --border-label foobar --preview "echo \$FZF_BORDER_LABEL // \$FZF_PREVIEW_LABEL" --preview-label barfoo --bind "space:change-border-label(barbaz)+change-preview-label(bazbar)+refresh-preview,enter:transform-border-label(echo 123)+transform-preview-label(echo 456)+refresh-preview"', :Enter
+    tmux.until do
+      assert_includes(_1[0], '─foobar─')
+      assert_includes(_1[1], '─barfoo─')
+      assert_includes(_1[2], ' foobar // barfoo ')
+    end
+    tmux.send_keys :Space
+    tmux.until do
+      assert_includes(_1[0], '─barbaz─')
+      assert_includes(_1[1], '─bazbar─')
+      assert_includes(_1[2], ' barbaz // bazbar ')
+    end
+    tmux.send_keys :Enter
+    tmux.until do
+      assert_includes(_1[0], '─123─')
+      assert_includes(_1[1], '─456─')
+      assert_includes(_1[2], ' 123 // 456 ')
+    end
+  end
+
   def test_info_separator_unicode
     tmux.send_keys 'seq 100 | fzf -q55', :Enter
     tmux.until { assert_includes(_1[-2], '  1/100 ─') }