bad40fb65b
Rename resolved→done (#1-4, #11), closed→done (#13, #18), open (post-core)→open (#7), mark #9 as superseded by #21.
43 lines
1.3 KiB
Markdown
43 lines
1.3 KiB
Markdown
# 03 — Implement direct command execution runtime (no shell)
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**Status:** done
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**Blocked by:** #02
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**Blocks:** #06, #07
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Implement the C runtime that executes commands when a backtick expression is evaluated.
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**Critical constraint:** do NOT spawn a shell (no `bash`, `dash`, `sh`, `system()`, `popen()`).
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## Return value
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Backtick expressions return a table:
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```lua
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local r = `ls -lha`
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r.code -- exit code (integer)
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r.stdout -- captured stdout (string)
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r.stderr -- captured stderr (string)
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```
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## Implementation approach
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- `fork()` + `execvp()` on Unix/macOS
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- Set up two pipes: one for stdout, one for stderr
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- In child: `dup2()` pipes onto fd 1 and fd 2, then `execvp(argv[0], argv)`
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- In parent: read both pipes into buffers, `waitpid()` for exit status
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- Build a Lua table with `code`, `stdout`, `stderr` fields and push onto stack
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- Depends on #04 (argv parsing) to tokenize the command string into argv[]
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## Error handling
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- Command not found → set `code` to an error value, `stderr` to error message
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- Permission denied → same
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- `fork()` failure → raise a Lua error
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## Open questions
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- New file (`lcmd.c` / `lcmd.h`) or add to an existing lib?
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- Signal handling during child execution
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- Binary output — return raw string bytes as-is?
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- Set `__tostring` metamethod on result table?
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