Benchmarks — the 9-shell race

Every number on this page is measured, not asserted, and reproducible with one command. Fairness rules and the measurement traps this harness has already fallen into are documented in bench/METHODOLOGY.md.

We build hellish plus a zoo of real shells — bash, dash, zsh, mksh, ksh, yash, busybox ash, fish — into one Docker image and race all nine on 17 portable POSIX workloads (make agnostic-bench). Ranking is the geometric mean of the best-of-7 time on each workload, so no single benchmark can skew it and warm-up noise is thrown away.

hellish ranks #3 of 9

#	shell	geomean	vs hellish
1	ksh	36.9 ms	0.55×	builtin-accelerated ¹
2	dash	51.4 ms	0.77×	the minimalist speed king
3	hellish	66.6 ms	1.00×	◀ us
4	busybox ash	72.8 ms	1.09×
5	zsh	114.1 ms	1.71×	hellish is 1.7× faster
6	bash	139.1 ms	2.09×	hellish is 2.1× faster
7	mksh	151.1 ms	2.27×
8	yash	185.6 ms	2.79×
9	fish	742.0 ms	11.14×

The honest summary: hellish is faster than 6 of the 8 other shells — including bash (2.1×) and every feature-rich shell (zsh, fish) — and lands just behind the two shells built to be minimal and nothing else. And it does this while carrying a bash-class feature surface those minimalist shells don't have (arrays, [[ =~ ]], ${v/p/r}, process substitution, job control, vi/emacs editing). That combination — minimalist speed, bash features — is the whole point.

¹ ksh93's #1 is partly an artifact: its recursion (fib18 54.6 ms vs everyone else's 2.4–4.8 seconds) and command-substitution rows are orders of magnitude off the field because ksh compiles/forklessly accelerates them — not comparable work. On the ordinary workloads it and hellish trade blows.

Where hellish wins, ties, and loses

No cherry-picking. Per-workload, best-of-7, lower is faster:

vs bash — hellish wins nearly everywhere it's tested:

area	hellish	bash	verdict
arithmetic loops	75 ms	161 ms	✅ 2.1× faster
string concat (grow)	16 ms	73 ms	✅ 4.6× faster
variable concat	75 ms	189 ms	✅ 2.5× faster
command substitution	161 ms	1211 ms	✅ 7.5× faster
test/[ ] string ops	69 ms	155 ms	✅ 2.3× faster
function calls	19 ms	47 ms	✅ 2.5× faster
parse a 50k-line script	55 ms	75 ms	✅ 1.4× faster

vs dash — the honest losses. dash is a tiny POSIX-only shell; matching it is the goal, not always reached:

area	hellish	dash	verdict
arithmetic loops	75 ms	66 ms	≈ within 15%
command substitution	161 ms	615 ms	✅ 3.8× faster
read loop	125 ms	724 ms	✅ 5.8× faster
function calls	19 ms	14 ms	➖ dash faster
parameter expansion	114 ms	60 ms	➖ dash faster
parse a 50k-line script	55 ms	29 ms	➖ dash faster

So: hellish beats dash on the fork- and I/O-heavy work (command substitution, read loops) and trails it on the pure-parse and pure-expansion micro-loops, where dash's do-almost-nothing design is hard to beat.

Memory

Peak resident set, median of 7 runs (make rss). hellish keeps a flat ~4 MB working set on loops — competitive with bash, sometimes tighter — and pays for its richer parser only where it parses a lot:

workload	hellish	bash	dash
startup	3.9 MB	3.8 MB	2.2 MB
arith loop	3.8 MB	3.9 MB	2.2 MB
string concat	3.9 MB	4.1 MB	2.2 MB
read loop	3.9 MB	3.9 MB	2.2 MB
parse 50k lines	11.6 MB	4.9 MB	2.2 MB

The parse-50k line is our one real memory cost: the lexer materialises the whole file's tokens up front. It's down from 158 MB → 20 MB → 11.6 MB over successive rounds (8-byte deque tokens, a borrowed input buffer); the remaining gap to bash is documented and the pull-lexer that closes it is planned in backlog.md.

Conformance — more POSIX than dash

Two independent third-party suites, run against bash --posix and dash (make conformance). hellish's rate is deliberately conservative — the Oils harness credits a "known-ok" annotation that exists for bash/dash but cannot exist for a shell it's never heard of, so we only ever count a hard pass.

mksh check.t (the ksh regression suite) — hellish now beats dash:

shell	passed
bash	292
hellish	218 🎉
dash	216

Oils spec suite (1622 cases spanning bash + POSIX features):

shell	hard passes	pass-rate
bash --posix	1311	85.1%
dash	977	68.5%
hellish --posix	1071	66.0% ᶜᵒⁿˢᵉʳᵛᵃᵗⁱᵛᵉ

hellish sits between dash and bash on raw Oils count — but Oils tests a pile of bash-isms dash simply lacks, so on the shared POSIX core hellish is much closer to bash than the headline number suggests, and it already passes more of the ksh suite than dash does.

So where does hellish rank, today?

dimension	tier	who's ahead
Speed	🥉 top-3 of 9	only ksh & dash (both minimalist specialists)
vs bash specifically	✅ faster	hellish wins ~2× on the geomean
Features	high	far beyond dash/busybox/mksh; near bash/zsh
Memory	good	flat ~4 MB; heavier only on big parses
POSIX conformance	solid	ahead of dash on mksh, behind bash overall

The one-line placement: hellish is a top-tier-fast shell that behaves like bash. Nothing else in the field pairs dash-adjacent speed with bash-class features — the minimalist shells (dash, busybox, mksh) are fast but bare, and the featureful ones (bash, zsh, fish) are slower. hellish sits in the empty quadrant between them.

Reproduce it

make agnostic-bench     # the 9-shell Docker race (needs docker; installs the shells for you)
make rss conformance    # memory + the two conformance suites
make charts             # redraw every SVG on this page from the raw artifacts

See also: Performance & Robustness · Architecture