added append and help mode

en

@@ -13,6 +13,21 @@ if test -z "$1"; then
 	printf "Usage: %s file...\n" "$argv0"
 fi
 
+help="Commands:\n\
+a – appends a line to the current buffer.\n\
+c – clears the screen.\n\
+d – deletes a line.\n\
+e – evaluates a command in the shell environment.\n\
+h – displays this help message.\n\
+i – inserts a line into the buffer at position line.\n\
+p – prints the current buffer.\n\
+q – terminates editing.\n\
+r – applies a regular expression to the current buffer.\n\
+w – writes the current buffer to the file.\n\
+\n\
+To learn more about a command verb, type \`h verb'.
+"
+
 while test -n "$1"; do
 	content="$(cat "$1")"
 	cat "$1"
@@ -22,12 +37,47 @@ while test -n "$1"; do
 		read -r command args
 
 		case $command in
+			"a")
+				read -r append
+				content="$(printf "%s\n%s" "$content" "$append")"
+				;;
 			"c")
 				clear
 				;;
 			"d")
 				printf "%s: d: Command not implemented.\n" "$argv0"
 				;;
+			"e")
+				eval "$args"
+				;;
+			"h")
+				if test -z "$args"; then
+					printf "$help\n"
+				else
+					printf "%s: Command-specific help not implemented.\n" "$argv0"
+					continue
+					case $args in
+						"c")
+							;;
+						"d")
+							;;
+						"e")
+							;;
+						"h")
+							;;
+						"i")
+							;;
+						"p")
+							;;
+						"q")
+							;;
+						"r")
+							;;
+						"w")
+							;;
+					esac
+				fi
+				;;
 			"i")
 				printf "%s: i: Command not implemented.\n" "$argv0"
 				;;
@@ -50,7 +100,7 @@ while test -n "$1"; do
 					break
 				fi
 				;;
-			"s")
+			"r")
 				content="$(printf "%s" "$content" | sed "$args")"
 				;;
 			"w")