Add plain format output to cli tables (apache#14546)

Add plain format output to cli tables so users can use standard 
linux utilities like awk, xargs etc.

closes: apache#14517

airflow/cli/cli_parser.py

@@ -184,9 +184,9 @@ def _check(value):
         "-o",
         "--output",
     ),
-    help="Output format. Allowed values: json, yaml, table (default: table)",
-    metavar="(table, json, yaml)",
-    choices=("table", "json", "yaml"),
+    help="Output format. Allowed values: json, yaml, plain, table (default: table)",
+    metavar="(table, json, yaml, plain)",
+    choices=("table", "json", "yaml", "plain"),
     default="table",
 )
 ARG_COLOR = Arg(

airflow/cli/simple_table.py

@@ -23,6 +23,7 @@
 from rich.console import Console
 from rich.syntax import Syntax
 from rich.table import Table
+from tabulate import tabulate
 
 from airflow.plugins_manager import PluginsDirectorySource
 from airflow.utils.platform import is_tty
@@ -62,6 +63,15 @@ def print_as_table(self, data: List[Dict]):
             table.add_row(*[str(d) for d in row.values()])
         self.print(table)
 
+    def print_as_plain_table(self, data: List[Dict]):
+        """Renders list of dictionaries as a simple table than can be easily piped"""
+        if not data:
+            self.print("No data found")
+            return
+        rows = [d.values() for d in data]
+        output = tabulate(rows, tablefmt="plain", headers=data[0].keys())
+        print(output)
+
     # pylint: disable=too-many-return-statements
     def _normalize_data(self, value: Any, output: str) -> Optional[Union[list, str, dict]]:
         if isinstance(value, (tuple, list)):
@@ -82,6 +92,7 @@ def print_as(self, data: List[Union[Dict, Any]], output: str, mapper: Optional[C
             "json": self.print_as_json,
             "yaml": self.print_as_yaml,
             "table": self.print_as_table,
+            "plain": self.print_as_plain_table,
         }
         renderer = output_to_renderer.get(output)
         if not renderer:

docs/apache-airflow/usage-cli.rst

@@ -182,6 +182,7 @@ Some Airflow commands like ``airflow dags list`` or ``airflow tasks states-for-d
 which allow users to change the formatting of command's output. Possible options:
 
   - ``table`` - renders the information as a plain text table
+  - ``simple`` - renders the information as simple table which can be parsed by standard linux utilities
   - ``json`` - renders the information in form of json string
   - ``yaml`` - render the information in form of valid yaml
 

docs/spelling_wordlist.txt

@@ -940,6 +940,7 @@ licence
 licences
 lifecycle
 lineterminator
+linux
 livy
 localExecutor
 localexecutor