generate-cmdlist.sh: do not shell out to "sed"

Replace the "sed" invocation in get_synopsis() with a pure-shell
version. This speeds up generate-cmdlist.sh significantly. Compared to
HEAD~ (old) and "master" we are, according to hyperfine(1):

  'sh generate-cmdlist.sh command-list.txt' ran
   12.69 ± 5.01 times faster than 'sh generate-cmdlist.sh.old command-list.txt'
   18.34 ± 3.03 times faster than 'sh generate-cmdlist.sh.master command-list.txt'

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

generate-cmdlist.sh

@@ -17,16 +17,6 @@ category_list () {
 	LC_ALL=C sort -u
 }
 
-get_synopsis () {
-	sed -n '
-		/^NAME/,/'"$1"'/H
-		${
-			x
-			s/.*'"$1"' - \(.*\)/N_("\1")/
-			p
-		}' "Documentation/$1.txt"
-}
-
 define_categories () {
 	echo
 	echo "/* Command categories */"
@@ -61,7 +51,18 @@ print_command_list () {
 	command_list "$1" |
 	while read cmd rest
 	do
-		printf "	{ \"$cmd\", $(get_synopsis $cmd), 0"
+		synopsis=
+		while read line
+		do
+			case "$line" in
+			"$cmd - "*)
+				synopsis=${line#$cmd - }
+				break
+				;;
+			esac
+		done <"Documentation/$cmd.txt"
+
+		printf '\t{ "%s", N_("%s"), 0' "$cmd" "$synopsis"
 		printf " | CAT_%s" $rest
 		echo " },"
 	done