Bash alias command substitution window resize bug

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed `Pilot.click` not working with `times` parameter https://github.com/Textualize/textual/pull/5398
+- Fixed terminal resize when standard output is not a tty: pipe (e.g. shell command substitution), regular file, /dev/null, etc https://github.com/Textualize/textual/pull/5417
 
 ### Added
 

src/textual/drivers/linux_driver.py

@@ -102,19 +102,33 @@ def _get_terminal_size(self) -> tuple[int, int]:
         Returns:
             The size of the terminal as a tuple of (WIDTH, HEIGHT).
         """
-        width: int | None = 80
-        height: int | None = 25
-        import shutil
+        try:
+            width = int(os.environ['COLUMNS'])
+        except (KeyError, ValueError):
+            width = 0
 
         try:
-            width, height = shutil.get_terminal_size()
-        except (AttributeError, ValueError, OSError):
+            height = int(os.environ['LINES'])
+        except (KeyError, ValueError):
+            height = 0
+
+        if width <= 0 or height <= 0:
+            # LINES and COLUMNS do not fully define terminal size: query the tty to get its actual size:
             try:
-                width, height = shutil.get_terminal_size()
+                size = os.get_terminal_size(self._file.fileno())
+                if width <= 0:
+                    width = size.columns
+                if height <= 0:
+                    height = size.lines
             except (AttributeError, ValueError, OSError):
                 pass
-        width = width or 80
-        height = height or 25
+
+            # Default to the de facto standard terminal size:
+            if width <= 0:
+                width = 80
+            if height <= 0:
+                height = 25
+
         return width, height
 
     def _enable_mouse_support(self) -> None:

src/textual/drivers/linux_inline_driver.py

@@ -61,19 +61,33 @@ def _get_terminal_size(self) -> tuple[int, int]:
         Returns:
             The size of the terminal as a tuple of (WIDTH, HEIGHT).
         """
-        width: int | None = 80
-        height: int | None = 25
-        import shutil
+        try:
+            width = int(os.environ['COLUMNS'])
+        except (KeyError, ValueError):
+            width = 0
 
         try:
-            width, height = shutil.get_terminal_size()
-        except (AttributeError, ValueError, OSError):
+            height = int(os.environ['LINES'])
+        except (KeyError, ValueError):
+            height = 0
+
+        if width <= 0 or height <= 0:
+            # LINES and COLUMNS do not fully define terminal size: query the tty to get its actual size:
             try:
-                width, height = shutil.get_terminal_size()
+                size = os.get_terminal_size(self._file.fileno())
+                if width <= 0:
+                    width = size.columns
+                if height <= 0:
+                    height = size.lines
             except (AttributeError, ValueError, OSError):
                 pass
-        width = width or 80
-        height = height or 25
+
+            # Default to the de facto standard terminal size:
+            if width <= 0:
+                width = 80
+            if height <= 0:
+                height = 25
+
         return width, height
 
     def _enable_mouse_support(self) -> None: