10. Diagnostics and Workflow

Lash tries to fail before Bash runs when a problem can be found statically.

Check first

lash check script.lash

check runs preprocessing, parsing, semantic analysis, warnings, and codegen feasibility checks without writing or running Bash output.

Run and compile

lash run script.lash arg1 arg2
lash compile script.lash -o script.sh
bash script.sh

run compiles to temporary Bash and executes it. compile writes the Bash output so you can inspect or run it yourself.

Format and watch

lash format .
lash format . --check
lash watch script.lash
lash watch src/

Use format --check in CI and watch when iterating on scripts.

Diagnostic groups

Diagnostic codes are grouped by phase:

• E000-E001: lexing and parsing
• E010-E015: preprocessor errors
• E110-E125: names, declarations, scope, traps, enums, and into
• E200-E203: type and container compatibility
• E300-E303: flow and constant-safety checks
• E400-E401: code generation feasibility
• W010, W500-W522: warnings

Common warnings

Warnings include:

• unreachable statements
• unused variables, parameters, and functions
• shadowed variables
• constant conditions
• suspicious missing interpolation
• malformed shell expansions
• suspicious heredoc payloads
• wait jobs with no tracked jobs
• non-positive constant wait targets
• missing or malformed shebangs

Warnings are there to make shell scripts less surprising. Treat them as design feedback, especially in automation code.

A useful debugging loop

1. Run lash check.
2. Fix the first real error.
3. Re-run lash check.
4. If generated Bash behavior is surprising, run lash compile and inspect the output.
5. Use --verbose on CLI commands when you need phase and tool resolution details.