db6f39a2a4
Defines syntax decisions and implementation plan across 7 issues:
- backtick command execution returning {code, stdout, stderr}
- ${expr} interpolation in backticks
- $SIGIL env var read/write
- argv parsing, piping, and redirection (future)
69 lines
1.7 KiB
Markdown
69 lines
1.7 KiB
Markdown
# 01 — Design and finalize syntax for all new features
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**Status:** resolved
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**Blocks:** #02, #04, #05
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## Backtick command execution
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Backtick expressions return a plain table with three fields:
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```lua
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local output = `ls -lha`
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print(
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output.code,
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output.stdout,
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output.stderr
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)
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```
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- `output.stdout` — captured stdout as a string
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- `output.stderr` — captured stderr as a string
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- `output.code` — integer exit code
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- No `__tostring` metamethod — access `.stdout` explicitly
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### String interpolation
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Backticks support `${expr}` interpolation:
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```lua
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local dir = "/tmp"
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local result = `ls -lha ${dir}`
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local pattern = "*.lua"
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local result2 = `find ${dir} -name ${pattern}`
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```
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`${expr}` evaluates the Lua expression, converts to string, and splices it into the command string before argv parsing.
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## Environment variables — `$` sigil
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```lua
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local dir = $PWD -- getenv("PWD") → string or nil
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$PWD = "/" -- setenv("PWD", "/")
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$MY_ENV_VAR = "data" -- setenv("MY_ENV_VAR", "data")
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```
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- `$NAME` as an expression → `getenv("NAME")`, returns string or `nil`
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- `$NAME = expr` as a statement → `setenv("NAME", tostring(expr))`
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- `$` followed by an identifier is a new token type in the lexer
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- Note: `$NAME` (env var) is distinct from `${expr}` inside backticks (interpolation)
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## Piping (future)
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```lua
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local result = `ls -l` | `grep ".lua"`
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```
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Challenge: `|` conflicts with Lua's bitwise OR. Pipes only valid between command expressions.
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## Redirection (future)
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```lua
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`ls -l` > "output.txt"
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`ls -l` >> "output.txt"
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`cmd` 2> "err.txt"
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`cmd` 2>&1
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`cmd` < "input.txt"
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```
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Challenge: `>` / `>>` conflict with Lua's comparison/shift operators. Only valid in command context.
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