Allow passing filename via environment variable.

README.md

@@ -75,6 +75,11 @@ Usage: bean-grep [OPTIONS] [PATTERN] FILENAME...
   To read from standard input, pass "-" as FILENAME, but beware that it
   implies on-disk buffering of stdin.
 
+  The FILENAME can alternatively be specified via the environment variable
+  BEANCOUNT_FILENAME. This allows not having to specify it explicitly every
+  time bean-grep is run. Only a single FILENAME is allowed to be specified
+  this way.
+
   All options can be set via environment variables, which is most useful if
   you want to override the defaults. Each environment variable
   consists of the prefix BEANGREP_ followed by the option name in uppercase.

src/beangrep/cli.py

@@ -6,6 +6,7 @@
 import logging
 import shutil
 import sys
+import os
 from tempfile import NamedTemporaryFile
 
 import beancount.loader  # type: ignore
@@ -68,7 +69,6 @@
 )
 @click.argument(
     "args",
-    required=True,
     nargs=-1,
     metavar="[PATTERN] FILENAME...",  # override metavar to show what is required
 )
@@ -278,10 +278,21 @@ def cli(
     logging.basicConfig(level=log_level)
 
     (pattern, filenames) = (None, [])
-    if len(args) == 1:  # len(args) == 0 should not happen due to required=True
-        filenames = list(args)
-    elif len(args) >= 2:
-        (pattern, filenames) = (args[0], list(args[1:]))
+    # click has has support for setting arguments via environment
+    # variables but I can't figure out how to make it work with
+    # beangrep's combination of optional pattern and variadic filenames.
+    # So we just roll it ourselves.
+    if os.getenv("BEANCOUNT_FILENAME"):
+        filenames = [os.getenv("BEANCOUNT_FILENAME")]
+        if len(args) == 1:
+            pattern = args[0]
+    else:
+        if len(args) == 0:
+            raise click.BadArgumentUsage("Must specify at least one beancount file.")
+        elif len(args) == 1:
+            filenames = list(args)
+        elif len(args) >= 2:
+            (pattern, filenames) = (args[0], list(args[1:]))
     if len(list(filter(lambda fname: fname == "-", filenames))) > 1:
         raise click.BadArgumentUsage(
             'Standard input ("-") cannot be specified multipled times'

tests/test_cli.py

@@ -264,7 +264,7 @@ def test_errors():
 
 # In theory any option could be set via envvars but let's just test the
 # most likely choices
-def test_envvars():
+def test_envvars_options():
     runner = CliRunner()
 
     result = runner.invoke(
@@ -288,3 +288,26 @@ def test_envvars():
         ).exit_code
         == 0
     )
+
+
+def test_envvar_beancount_file():
+    runner = CliRunner()
+
+    assert (
+        runner.invoke(
+            cli, env={"BEANCOUNT_FILENAME": "does_not_exist.beancount"}
+        ).exit_code
+        == 2
+    )
+
+    result = runner.invoke(
+        cli, ["--amount", "=76.81 USD"], env={"BEANCOUNT_FILENAME": SAMPLE_LEDGER}
+    )
+    assert result.exit_code == 0
+    assert "Verizon Wireless" in result.output
+
+    result = runner.invoke(
+        cli, ["^a-day-in"], env={"BEANCOUNT_FILENAME": SAMPLE_LEDGER}
+    )
+    assert result.exit_code == 0
+    assert "Mercadito" in result.output