feat: run commands to get settings

src/scriv/config.py

@@ -13,6 +13,7 @@
 from .exceptions import ScrivException
 from .literals import find_literal
 from .optional import tomllib
+from .shell import run_shell_command
 
 logger = logging.getLogger(__name__)
 
@@ -363,6 +364,7 @@ def resolve_value(self, value: str) -> str:
         Prefixes:
             "file:" read the content from a file.
             "literal:" read a literal string from a file.
+            "command:" read the output of a shell command.
 
         """
         value = value.replace("${config:format}", self._options.format)
@@ -392,6 +394,14 @@ def resolve_value(self, value: str) -> str:
                     + f"{value!r}"
                 )
             value = found
+        elif value.startswith("command:"):
+            cmd = value.partition(":")[2].strip()
+            ok, out = run_shell_command(cmd)
+            if not ok:
+                raise ScrivException(f"Command {cmd!r} failed:\n{out}")
+            if out.count("\n") == 1:
+                out = out.rstrip("\r\n")
+            value = out
         return value
 
     def read_file_value(self, file_name: str) -> str:

src/scriv/shell.py

@@ -46,3 +46,22 @@ def run_simple_command(cmd: Union[str, List[str]]) -> str:
     if not ok:
         return ""
     return out.strip()
+
+
+def run_shell_command(cmd: str) -> CmdResult:
+    """
+    Run a command line with a shell.
+    """
+    logger.debug(f"Running shell command {cmd!r}")
+    proc = subprocess.run(
+        cmd,
+        shell=True,
+        check=False,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+    )
+    output = proc.stdout.decode("utf-8")
+    logger.debug(
+        f"Command exited with {proc.returncode} status. Output: {output!r}"
+    )
+    return proc.returncode == 0, output

tests/test_config.py

@@ -344,3 +344,43 @@ def test_no_toml_installed_no_settings(self, temp_dir):
         with without_module(scriv.config, "tomllib"):
             config = Config.read()
         assert config.categories[0] == "Removed"
+
+
+@pytest.mark.parametrize(
+    "cmd_output, result",
+    [
+        ("Xyzzy 2 3\n", "Xyzzy 2 3"),
+        ("Xyzzy 2 3\nAnother line\n", "Xyzzy 2 3\nAnother line\n"),
+    ],
+)
+def test_command_running(mocker, cmd_output, result):
+    # Any setting can be the output of a command.
+    mocker.patch(
+        "scriv.config.run_shell_command", lambda cmd: (True, cmd_output)
+    )
+    text = Config(output_file="command: doesnt-matter").output_file
+    assert text == result
+
+
+def test_real_command_running():
+    text = Config(output_file="command: echo Xyzzy 2 3").output_file
+    assert text == "Xyzzy 2 3"
+
+
+@pytest.mark.parametrize(
+    "bad_cmd, msg_rx",
+    [
+        (
+            "xyzzyplugh",
+            "Couldn't read 'output_file' setting: Command 'xyzzyplugh' failed:",
+        ),
+        (
+            "'hi!2><",
+            "Couldn't read 'output_file' setting: Command \"'hi!2><\" failed:",
+        ),
+    ],
+)
+def test_bad_command(fake_run_command, bad_cmd, msg_rx):
+    # Any setting can be the output of a command.
+    with pytest.raises(ScrivException, match=msg_rx):
+        _ = Config(output_file=f"command: {bad_cmd}").output_file