用 Python shutil.which 排查命令找不到：PATH 顺序与自动化预检

python3 --version
mkdir command-path-demo
cd command-path-demo
python3 - <<'PY_SETUP'
from pathlib import Path
for directory, label in [("first bin", "FIRST"), ("second bin", "SECOND")]:
    folder = Path(directory)
    folder.mkdir()
    tool = folder / "demo-tool"
    tool.write_text(f"#!/bin/sh\nprintf '{label}\\n'\n", encoding="utf-8")
    tool.chmod(0o755)
Path("empty bin").mkdir()
PY_SETUP

"""Inspect bare command names on an explicit Linux PATH without running them."""
import argparse
import json
import os
import shutil
import sys


def inspect_commands(names, search_path):
    if search_path is None:
        raise ValueError("PATH is unset; pass --path explicitly")
    entries = search_path.split(os.pathsep)
    if any(not entry or not os.path.isabs(entry) for entry in entries):
        raise ValueError("PATH entries must be nonempty absolute paths")
    if "\0" in search_path:
        raise ValueError("PATH must not contain NUL")
    if any(not name or "/" in name or "\0" in name for name in names):
        raise ValueError("use bare command names, not file paths")
    results = []
    for name in names:
        hit = shutil.which(name, path=search_path)
        results.append({"command": name, "path": hit})
    return {"results": results, "ok": all(row["path"] is not None for row in results)}


def main():
    cli = argparse.ArgumentParser(description=__doc__, allow_abbrev=False)
    cli.add_argument("--path", default=os.environ.get("PATH"),
                     help="PATH to inspect; defaults to the process PATH")
    cli.add_argument("commands", nargs="+", help="bare executable names")
    args = cli.parse_args()
    try:
        report = inspect_commands(args.commands, args.path)
    except (OSError, ValueError) as exc:
        print(f"ERROR: {exc}", file=sys.stderr)
        return 2
    print(json.dumps(report))
    return 0 if report["ok"] else 1


if __name__ == "__main__":
    raise SystemExit(main())

python3 check_commands.py --help
python3 check_commands.py --path "$PWD/first bin:$PWD/second bin" demo-tool
python3 check_commands.py --path "$PWD/second bin:$PWD/first bin" demo-tool

from pathlib import Path
import json
import os
import subprocess
import sys

root = Path.cwd()
first = str(root / "first bin")
second = str(root / "second bin")
empty = str(root / "empty bin")
script = str(root / "check_commands.py")
before = {p: p.read_bytes() for p in root.glob("* bin/demo-tool")}


def check(arguments, expected, env=None):
    result = subprocess.run(
        [sys.executable, script, *arguments],
        capture_output=True, text=True, env=env, check=False,
    )
    assert result.returncode == expected, result
    if expected == 2:
        assert result.stdout == "" and "ERROR:" in result.stderr, result
        return None
    assert result.stderr == "", result.stderr
    return json.loads(result.stdout)


for path, directory in [(first + ":" + second, first), (second + ":" + first, second)]:
    data = check(["--path", path, "demo-tool"], 0)
    assert data["results"][0]["path"] == directory + "/demo-tool"
    assert data["ok"] is True
print("PASS: PATH order selects the first executable")

data = check(["--path", empty, "demo-tool"], 1)
assert data == {"results": [{"command": "demo-tool", "path": None}], "ok": False}
print("PASS: missing executable returns 1")

for path in ["", ".", first + ":", first + ":relative"]:
    check(["--path", path, "demo-tool"], 2)
check(["--path", first, "./demo-tool"], 2)
env = os.environ.copy()
env.pop("PATH", None)
check(["demo-tool"], 2, env=env)
print("PASS: ambiguous PATH and non-bare names rejected")
assert all(p.read_bytes() == content for p, content in before.items())
print("PASS: fixture content unchanged")

PASS: PATH order selects the first executable
PASS: missing executable returns 1
PASS: ambiguous PATH and non-bare names rejected
PASS: fixture content unchanged

if python3 check_commands.py --path "$PWD/first bin" demo-tool; then
  printf 'Preflight passed; now validate the real tool version and run the job.\n'
else
  status=$?
  printf 'Stopped before the job; preflight exit=%s\n' "$status" >&2
  exit "$status"
fi