Add $FZF_POS environment variable

Close #2175
Close #3753

CHANGELOG.md

@@ -3,6 +3,13 @@ CHANGELOG
 
 0.51.0
 ------
+- Added a new environment variable `$FZF_POS` exported to the child processes. It's the vertical position of the cursor in the list starting from 1.
+  ```sh
+  # Toggle selection to the top or to the bottom
+  seq 30 | fzf --multi --bind 'load:pos(10)' \
+    --bind 'shift-up:transform:for _ in $(seq $FZF_POS $FZF_MATCH_COUNT); do echo -n +toggle-up; done' \
+    --bind 'shift-down:transform:for _ in $(seq 1 $FZF_POS); do echo -n +toggle-down; done'
+  ```
 - Added `--with-shell` option to start child processes with a custom shell command and flags
   ```sh
   gem list | fzf --with-shell 'ruby -e' \

man/man1/fzf.1

@@ -984,6 +984,8 @@ fzf exports the following environment variables to its child processes.
 .br
 .BR FZF_SELECT_COUNT "    Number of selected items"
 .br
+.BR FZF_POS "             Vertical position of the cursor in the list starting from 1"
+.br
 .BR FZF_QUERY "           Current query string"
 .br
 .BR FZF_PROMPT "          Prompt string"

src/terminal.go

@@ -856,6 +856,7 @@ func (t *Terminal) environ() []string {
 	env = append(env, fmt.Sprintf("FZF_SELECT_COUNT=%d", len(t.selected)))
 	env = append(env, fmt.Sprintf("FZF_LINES=%d", t.areaLines))
 	env = append(env, fmt.Sprintf("FZF_COLUMNS=%d", t.areaColumns))
+	env = append(env, fmt.Sprintf("FZF_POS=%d", util.Min(t.merger.Length(), t.cy+1)))
 	return env
 }
 

test/test_go.rb

@@ -3250,6 +3250,17 @@ class TestGoFZF < TestBase
     tmux.send_keys :Up
     tmux.until { |lines| assert_includes lines, '> 2' }
   end
+
+  def test_fzf_pos
+    tmux.send_keys "seq 100 | #{FZF} --preview 'echo $FZF_POS / $FZF_MATCH_COUNT'", :Enter
+    tmux.until { |lines| assert(lines.any? { |line| line.include?('1 / 100') }) }
+    tmux.send_keys :Up
+    tmux.until { |lines| assert(lines.any? { |line| line.include?('2 / 100') }) }
+    tmux.send_keys '99'
+    tmux.until { |lines| assert(lines.any? { |line| line.include?('1 / 1') }) }
+    tmux.send_keys '99'
+    tmux.until { |lines| assert(lines.any? { |line| line.include?('0 / 0') }) }
+  end
 end
 
 module TestShell