perf(doc): parse assertion docs in a single awk pass

CHANGELOG.md

@@ -16,6 +16,7 @@
 - `--jobs auto` / `-j auto` caps parallel concurrency at the CPU core count (portable across Linux/macOS/BSD); the default stays unlimited (#766)
 
 ### Changed
+- `bashunit doc` no longer forks an `echo | sed` pipe per line of the assertion docs: a single awk pass prints the same bytes in ~50ms instead of ~5s (#832)
 - Multi-file runs are no longer quadratic in file count: each file's test functions are unset once the file has been processed, so test subshells stop forking an ever-growing shell. bashunit's own 63-file unit suite: ~64s -> ~22s sequential, ~26s -> ~7s parallel (#829)
 - Major performance work with no behaviour change: assertions, per-test execution, per-file discovery, cold start and parallel result publishing are now (near) fork-free, snapshots and `--tag` scans are cached, and quadratic failure rendering is single-pass. Benchmarks on bash 3.2: 100x10 `assert_equals` ~1.50s -> ~0.76s, 500 snapshot assertions ~7.5s -> ~3.0s, 100 tagged tests ~2.92s -> ~0.68s, and bashunit's own acceptance suite ~61s -> ~17s (#761-#764, #772-#775, #798, #801-#807, #809, #810, #813, #817)
 - Per-test timing now defaults to `auto` (`BASHUNIT_SHOW_EXECUTION_TIME=true|false|auto`): shown only when the clock is fork-free, avoiding `perl` forks on bash 3.2; `--profile`/`--verbose`/reports still measure (see `adrs/adr-008-auto-skip-per-test-timing.md`) (#765)

src/doc.sh

@@ -9,58 +9,49 @@ function bashunit::doc::get_embedded_docs() {
   # __BASHUNIT_EMBEDDED_DOCS_END__
 }
 
+# Single awk pass over the embedded docs: the previous line-by-line shell loop
+# forked an `echo | sed` pipe per line (~3.2k forks, ~5s for the ~1.6k-line
+# docs page); one awk fork does the same work in milliseconds (#832).
 function bashunit::doc::print_asserts() {
   local filter="${1:-}"
-  local docstring=""
-  local fn=""
-  local should_print=0
 
-  local line
-  while IFS='' read -r line || [ -n "$line" ]; do
-    fn=$(echo "$line" | sed -n 's/^## \([A-Za-z0-9_]*\).*/\1/p')
-    # Only treat assertion headings as doc entries; skip prose sections
-    # like "## Related" that are part of the documentation page but not asserts.
-    case "$fn" in
-    assert* | bashunit*) ;;
-    *) fn="" ;;
-    esac
-    if [ -n "$fn" ]; then
-      local _match=0
-      if [ -z "$filter" ]; then
-        _match=1
-      else
-        case "$fn" in *"$filter"*) _match=1 ;; esac
-      fi
-      if [ "$_match" -eq 1 ]; then
-        should_print=1
-        echo "$line"
-        docstring=""
-      else
-        should_print=0
-      fi
-      continue
-    fi
+  bashunit::doc::get_embedded_docs | awk -v filter="$filter" '
+    {
+      if ($0 ~ /^## /) {
+        # Heading word: the leading [A-Za-z0-9_]* run after "## ". Only
+        # assert*/bashunit* headings are doc entries; prose headings like
+        # "## Related" fall through and are treated as regular content.
+        fn = substr($0, 4)
+        sub(/[^A-Za-z0-9_].*$/, "", fn)
+        if (fn ~ /^(assert|bashunit)/) {
+          if (filter == "" || index(fn, filter) > 0) {
+            should_print = 1
+            print $0
+            doc = ""
+          } else {
+            should_print = 0
+          }
+          next
+        }
+      }
 
-    if ((should_print)); then
-      # Check for code fence using pattern matching instead of regex
-      # Avoids backtick escaping issues in Bash 3.0
-      case "$line" in
-      '```'*)
-        echo "--------------"
-        echo "$docstring"
-        should_print=0
-        continue
-        ;;
-      esac
+      if (should_print) {
+        if ($0 ~ /^```/) {
+          print "--------------"
+          print doc
+          should_print = 0
+          next
+        }
+        if ($0 ~ /^::: code-group/) next
 
-      case "$line" in
-      "::: code-group"*) continue ;;
-      esac
-
-      # Remove markdown link brackets and anchor tags
-      line="${line//[\[\]]/}"
-      line="$(sed -E 's/ *\(#[-a-z0-9]+\)//g' <<<"$line")"
-      docstring="$docstring$line"$'\n'
-    fi
-  done <<<"$(bashunit::doc::get_embedded_docs)"
+        # Remove markdown link brackets and anchor tags. The bracket class
+        # uses the POSIX []][ idiom: busybox awk (Alpine) rejects
+        # backslash-escaped brackets inside a bracket expression.
+        line = $0
+        gsub(/[][]/, "", line)
+        gsub(/ *\(#[-a-z0-9]+\)/, "", line)
+        doc = doc line "\n"
+      }
+    }
+  '
 }

tests/acceptance/bashunit_doc_forks_test.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Regression guard for #832. `bashunit doc` used to fork an `echo | sed` pipe
+# for every line of the ~1.6k-line assertions.md (plus another `sed` per
+# printed docstring line): ~3200 forks and ~5s wall to print a text file. The
+# doc path must parse the embedded docs in a single awk pass instead.
+function test_doc_command_does_not_fork_sed_per_line() {
+  if bashunit::check_os::is_windows; then
+    bashunit::skip "process tracing is unreliable under Git Bash" && return
+  fi
+
+  local trace
+  trace="$(PS4='+ ' bash -x ./bashunit doc equals 2>&1 >/dev/null)"
+
+  # Count real `sed` process executions. The doc path invokes `sed` via PATH
+  # (not a pinned absolute binary), so the traced command token is a bare
+  # `sed` — match both forms; `command -v sed` is a builtin and never shows.
+  local sed_forks
+  sed_forks="$(printf '%s\n' "$trace" | grep -cE '^\++ +(/[^ ]*/)?sed ' || true)"
+
+  assert_equals 0 "$sed_forks"
+}