Awk exit code portability across implementations and shell notification handling

This question explores whether awk can signal matching events to a downstream shell process without polluting stdout, given implementation-dependent exit-code and error-variable behavior. Awk scripts often need to communicate pattern matches upstream, but the mechanism chosen affects both signal clarity and pipeline compatibility.

POSIX defines exit codes as numeric values; gawk preserves arbitrary strings in the EXITCODE variable after an exit statement, while mawk and nawk truncate to the 0-255 range, creating a portability gap for cross-implementation scripts. The getline command similarly sets ERRNO on I/O failure, but gawk populates it with system-error strings whereas mawk may leave it empty or unset, representing implementation-defined behavior that affects error-aware alert logic. The default record separator RS is the newline, yet multi-byte RS handling varies between awk builds, potentially shifting pattern-matching boundaries in alert rules.

Can conditional printf combined with exit effectively isolate matching records for downstream notification? How does ERRNO inconsistency between implementations affect the robustness of error-triggered alerts? What record-separator conventions ensure consistent pattern matching when awk output is consumed by shell-based notification pipelines?