perplexity-agent-mcp: Instructions file for Codex

Rule: Read the Startup Files First

Read @README.md before taking any action.

Rule: Execute Commands from Arrays, Not Strings

Store commands in arrays, not strings

When Bash expands a string variable, quotes inside become literal characters and whitespace triggers word splitting:

# BAD
CMD="echo \"hello world\""
$CMD  # outputs: "hello world" (with literal quotes)

# GOOD: array preserves argument boundaries
CMD=(echo "hello world")
"${CMD[@]}"  # outputs: hello world

Never interpolate variables into shell strings

Variables interpolated into shell strings — sh -c, bash -c, eval, ssh host — are reparsed by the shell. Characters like $(...), backticks, or ; in the value execute as code — an injection vector:

# BAD: if VAR contains $(malicious), it executes
sh -c "$VAR --write"

# GOOD: direct execution, no shell interpretation
"${CMD[@]}" --write

# GOOD: with xargs, execute the array directly
find . -name '*.js' -print0 | xargs -0 "${CMD[@]}" --write --

When you need shell features (pipes, redirects), use the exec "$@" pattern to pass arguments as positional parameters instead of interpolating them:

# GOOD: arguments passed as $@, not interpolated into the string; the redirect is why sh -c is needed
find . -name '*.js' -print0 | xargs -0 sh -c 'exec "$@" >> format.log 2>&1' _ "${CMD[@]}" --write --

The _ occupies $0 (the script name), leaving $@ for the command and arguments.

Rule: Avoid Leaky Abstractions

Design interfaces around what callers need, not how the system works internally. An abstraction is leaky when using it correctly requires knowledge of underlying storage, infrastructure, or error behavior — a connection string in a method signature, a transaction handle in a return type, an error that only makes sense one layer down, or two similar-looking methods where one reads memory and the other crosses the network. Keep signatures consistent, return domain types instead of backend artifacts, and inject infrastructure dependencies through constructors rather than method parameters.