2 files changed, 37 insertions, 0 deletions
diff --git a/internal/tui/tui.go b/internal/tui/tui.go
index c9f1241..e7872c8 100644
--- a/internal/tui/tui.go
+++ b/internal/tui/tui.go
@@ -36,6 +36,21 @@ func Colour(w io.Writer) bool {
 	return !noColour
 }
 
+// Width is the terminal's column count, 0 when w is not a terminal or the
+// size cannot be read: callers wrap text to it, and treat 0 as "never
+// wrap", which keeps output piped to a file one field per line.
+func Width(w io.Writer) int {
+	f, ok := w.(*os.File)
+	if !ok || !isTerminal(int(f.Fd())) {
+		return 0
+	}
+	cols, _, err := termSize(int(f.Fd()))
+	if err != nil {
+		return 0
+	}
+	return cols
+}
+
 // height is the terminal's row count, 0 when it is not a terminal or the
 // size cannot be read.
 func height(w io.Writer) int {
diff --git a/internal/tui/tui_test.go b/internal/tui/tui_test.go
index a3640ac..614f239 100644
--- a/internal/tui/tui_test.go
+++ b/internal/tui/tui_test.go
@@ -51,6 +51,28 @@ func TestHeight(t *testing.T) {
 	}
 }
 
+// TestWidth: the terminal's column count, and 0 wherever there is no
+// terminal to wrap to, so a caller treats 0 as "never wrap".
+func TestWidth(t *testing.T) {
+	var buf bytes.Buffer
+	if w := Width(&buf); w != 0 {
+		t.Errorf("Width on a non-terminal writer = %d, want 0", w)
+	}
+
+	oldT, oldS := isTerminal, termSize
+	t.Cleanup(func() { isTerminal, termSize = oldT, oldS })
+	isTerminal = func(fd int) bool { return true }
+	termSize = func(fd int) (int, int, error) { return 132, 24, nil }
+	if w := Width(os.Stdout); w != 132 {
+		t.Errorf("Width = %d, want 132", w)
+	}
+
+	termSize = func(fd int) (int, int, error) { return 0, 0, os.ErrInvalid }
+	if w := Width(os.Stdout); w != 0 {
+		t.Errorf("Width when the size cannot be read = %d, want 0", w)
+	}
+}
+
 func TestPageUsesPagerOnlyWhenTaller(t *testing.T) {
 	dir := t.TempDir()
 	marker := filepath.Join(dir, "paged")