feat: streamable stdout

.gitignore

@@ -4,3 +4,4 @@ jbang.egg-info
 jbang/__pycache__
 __pycache__
 .coverage
+.venv

.justfile

@@ -1,12 +1,12 @@
 test:
-    source .venv/bin/activate
+    .venv/bin/activate
     #pip3 install -e .
     uv pip install -e ".[test]"
 
     echo Running tests with no jbang in PATH
     PATH=$(echo $PATH | tr ':' '\n' | grep -v "\.jbang/bin" | tr '\n' ':' | sed 's/:$//') .venv/bin/python -m pytest  -o log_cli_level=DEBUG  -o log_cli=true
 
 release:
-    source .venv/bin/activate
+    .venv/bin/activate
     uv pip install setuptools
     gh release create `python3 setup.py --version` --generate-notes

jbang/__init__.py

@@ -1,6 +1,6 @@
-from .jbang import exec, spawnSync, main, quote
+from .jbang import exec, spawnSync, main, quote, popen
 
-__all__ = ['exec', 'spawnSync', 'main', 'quote']
+__all__ = ['exec', 'spawnSync', 'main', 'quote', 'popen']
 
 if __name__ == "__main__":
     main()

jbang/jbang.py

@@ -199,6 +199,30 @@ def spawnSync(args: Union[str, List[str]]) -> Any:
             2
         )
 
+def popen(args: Union[str, List[str]]) -> subprocess.Popen:
+    """Returns a reference to a subprocess.Popen instance for streaming stdout."""
+    log.debug(f"trying to execute popen command: {args}")
+
+    cmdLine = _getCommandLine(args)
+
+    if not cmdLine:
+        print("Could not locate a way to run jbang. Try installing jbang manually and try again.")
+        raise Exception(
+            "Could not locate a way to run jbang. Try installing jbang manually and try again.",
+            2
+        )
+
+    return subprocess.Popen(
+        cmdLine,
+        shell=True,
+        stdin=subprocess.DEVNULL,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+        bufsize=1,
+        universal_newlines=True,
+    )
+
 def main():
     """Command-line entry point for jbang-python."""
     log.debug("Starting jbang-python CLI")

tests/test_jbang.py

@@ -1,10 +1,48 @@
 import sys
 
+from pathlib import Path 
 import pytest
 
 import jbang
 from jbang.jbang import CommandResult
 
+@pytest.fixture
+def java_hello(tmp_path: Path):
+    code = """
+    public class HelloWorld {
+        public static void main(String[] args) {
+            System.out.print("Hello, world!");
+        }
+    }    
+    """
+
+    file_path = tmp_path / "HelloWorld.java"
+    file_path.write_text(code.strip())
+    return file_path
+
+@pytest.fixture
+def streamable_java_hello(tmp_path: Path):
+    code = """
+    import java.io.*;
+    import java.util.Random;
+
+    public class HelloStreamable {
+        static final BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out), 1 << 20);
+        public static void main(String[] args) throws Exception {
+            String message = \"Hello, world!\";
+            Random rand = new Random();
+            for (int i = 0; i < message.length(); i++){
+                out.write(message.charAt(i));
+                out.newLine();
+                out.flush();
+                Thread.sleep(rand.nextInt(3));
+            }
+        }
+    }
+    """
+    file_path = tmp_path / "HelloStreamable.java"
+    file_path.write_text(code.strip())
+    return file_path
 
 def test_version_command():
     """Test version command."""
@@ -60,6 +98,23 @@ def test_invalid_java_version():
     out = jbang.exec('--java invalid properties@jbangdev java.version')
     assert 'Invalid version' in out.stderr
 
+def test_popen_single_write(java_hello):
+    process = jbang.popen(str(java_hello))
+    process.wait()
+
+    assert process.returncode == 0
+    assert process.stdout.readlines()[0] == "Hello, world!"
+
+def test_popen_streamable_java_hello(streamable_java_hello):
+    process = jbang.popen(str(streamable_java_hello))
+    rows = []
+    message = "Hello, world!"
+    for i, line in enumerate(process.stdout):
+        assert line.rstrip("\n") == message[i]
+
+    return_code = process.wait()
+    assert return_code == 0
+
 @pytest.mark.skipif(sys.platform == 'win32', reason="Quote tests behave differently on Windows")
 class TestQuoting:
     def test_quote_empty_string(self):