feat(scripts): provide `diagrams` CLI

This change addresses https://github.com/mingrammer/diagrams/issues/369
while providing a simple CLI entry point which can be used outside the
virtual environment of the installed package.

This works well with for example with [pipx](https://pipxproject.github.io/pipx/).

diagrams/cli.py

@@ -0,0 +1,31 @@
+import argparse
+import sys
+
+
+def run() -> int:
+    parser = argparse.ArgumentParser(
+        description="Run diagrams code files in a diagrams environment.",
+    )
+    parser.add_argument(
+        "paths",
+        metavar="path",
+        type=str,
+        nargs="+",
+        help="a Python file containing diagrams code",
+    )
+    args = parser.parse_args()
+
+    for path in args.paths:
+        print(path)
+        with open(path) as f:
+            exec(f.read())
+
+    return 0
+
+
+def main():
+    sys.exit(run())
+
+
+if __name__ == "__main__":
+    main()

docs/getting-started/installation.md

@@ -18,6 +18,9 @@ $ pipenv install diagrams
 
 # using poetry
 $ poetry add diagrams
+
+# using pipx
+$ pipx install diagrams
 ```
 
 ## Quick Start
@@ -43,6 +46,21 @@ $ python diagram.py
 
 It will be saved as `web_service.png` on your working directory.
 
+### CLI
+
+If the `diagrams` CLI has been installed system wide (i.e. with [pipx](https://pipxproject.github.io/pipx/)),
+then the preceding command is equivalent to this.
+
+```shell
+$ diagrams diagram.py
+```
+
+Furthermore you can execute multiple files at once
+
+```shell
+$ diagrams diagram1.py diagram2.py
+```
+
 ## Next
 
 See more [Examples](/docs/getting-started/examples) or see [Guides](/docs/guides/diagram) page for more details.

pyproject.toml

@@ -9,6 +9,9 @@ homepage = "https://diagrams.mingrammer.com"
 repository = "https://github.com/mingrammer/diagrams"
 include = ["resources/**/*"]
 
+[tool.poetry.scripts]
+diagrams="diagrams.cli:main"
+
 [tool.poetry.dependencies]
 python = "^3.6"
 graphviz = ">=0.13.2,<0.17.0"