posix shell: use /bin/sh instead of bash

This uses the systems default shell:
- Ubuntu: dash
- Fedora: bash

Since bash is invoked via /bin/sh, it operates in POSIX mode:
  https://tiswww.case.edu/php/chet/bash/POSIX

- remove '# Ignore the expand_aliases command in zshell.'
  Not needed because the shell operates in POSIX mode
- [[ is bashism -> use [
- autostart_files=( $autostart_file_match )
  is not supported in dash, so use 'ls'
- shellcheck runs the dash flavor, since dash is a minimalistic shell.

Tested on dash & bash.

ROMFS/px4fmu_common/init.d-posix/rcS

@@ -5,7 +5,7 @@
 # shellcheck disable=SC1091
 . px4-alias.sh
 
-SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+SCRIPT_DIR="$(CDPATH='' cd -- "$(dirname -- "$0")" && pwd)"
 
 #
 # Main SITL startup script
@@ -149,10 +149,7 @@ then
 fi
 
 # Autostart ID
-autostart_file_match="etc/init.d-posix/$(param show -q SYS_AUTOSTART)_*"
-# shellcheck disable=SC2206
-autostart_files=( $autostart_file_match )
-autostart_file="${autostart_files[0]}" # use first match, but there should really only be one
+autostart_file=$( ls -- etc/init.d-posix/"$(param show -q SYS_AUTOSTART)"_* )
 if [ ! -e "$autostart_file" ]; then
 	echo "Error: no autostart file found"
 	exit -1

Tools/run-shellcheck.sh

@@ -32,6 +32,7 @@ shellcheck -x \
 	-e SC2148 \
 	-e SC2166 \
 	-e SC2039 \
+	--shell=dash \
 	$scripts
 ret=$?
 if [ $ret -ne 0 ]; then

platforms/posix/CMakeLists.txt

@@ -7,9 +7,9 @@ get_property(module_libraries GLOBAL PROPERTY PX4_MODULE_LIBRARIES)
 
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 
-set(PX4_BASH_PREFIX "px4-")
+set(PX4_SHELL_COMMAND_PREFIX "px4-")
 
-add_definitions("-DPX4_BASH_PREFIX=\"${PX4_BASH_PREFIX}\"")
+add_definitions("-DPX4_SHELL_COMMAND_PREFIX=\"${PX4_SHELL_COMMAND_PREFIX}\"")
 
 px4_posix_generate_builtin_commands(
 	OUT apps
@@ -18,7 +18,7 @@ px4_posix_generate_builtin_commands(
 px4_posix_generate_alias(
 	OUT ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/px4-alias.sh
 	MODULE_LIST ${module_libraries}
-	PREFIX ${PX4_BASH_PREFIX}
+	PREFIX ${PX4_SHELL_COMMAND_PREFIX}
 )
 
 if (("${BOARD}" STREQUAL "eagle") OR ("${BOARD}" STREQUAL "excelsior"))
@@ -97,7 +97,7 @@ endif()
 # Module Symlinks
 px4_posix_generate_symlinks(
 	MODULE_LIST ${module_libraries}
-	PREFIX ${PX4_BASH_PREFIX}
+	PREFIX ${PX4_SHELL_COMMAND_PREFIX}
 	TARGET px4
 )
 

platforms/posix/src/main.cpp

@@ -99,8 +99,7 @@ static void register_sig_handler();
 static void set_cpu_scaling();
 static int create_symlinks_if_needed(std::string &data_path);
 static int create_dirs();
-static int run_startup_bash_script(const std::string &commands_file, const std::string &absolute_binary_path,
-				   int instance);
+static int run_startup_script(const std::string &commands_file, const std::string &absolute_binary_path, int instance);
 static std::string get_absolute_binary_path(const std::string &argv0);
 static void wait_to_exit();
 static bool is_already_running(int instance);
@@ -123,7 +122,7 @@ int main(int argc, char **argv)
 	bool pxh_off = false;
 
 	/* Symlinks point to all commands that can be used as a client with a prefix. */
-	const char prefix[] = PX4_BASH_PREFIX;
+	const char prefix[] = PX4_SHELL_COMMAND_PREFIX;
 	int path_length = 0;
 
 	std::string absolute_binary_path; // full path to the px4 binary being executed
@@ -275,7 +274,7 @@ int main(int argc, char **argv)
 		px4::init_once();
 		px4::init(argc, argv, "px4");
 
-		ret = run_startup_bash_script(commands_file, absolute_binary_path, instance);
+		ret = run_startup_script(commands_file, absolute_binary_path, instance);
 
 		// We now block here until we need to exit.
 		if (pxh_off) {
@@ -479,16 +478,12 @@ std::string get_absolute_binary_path(const std::string &argv0)
 	return pwd() + "/" + base;
 }
 
-int run_startup_bash_script(const std::string &commands_file, const std::string &absolute_binary_path,
-			    int instance)
+int run_startup_script(const std::string &commands_file, const std::string &absolute_binary_path,
+		       int instance)
 {
-#ifdef __DF_BEBOP
-	std::string bash_command("sh ");
-#else
-	std::string bash_command("bash ");
-#endif
+	std::string shell_command("/bin/sh ");
 
-	bash_command += commands_file + ' ' + std::to_string(instance);
+	shell_command += commands_file + ' ' + std::to_string(instance);
 
 	// Update the PATH variable to include the absolute_binary_path
 	// (required for the px4-alias.sh script and px4-* commands).
@@ -526,12 +521,12 @@ int run_startup_bash_script(const std::string &commands_file, const std::string
 	}
 
 
-	PX4_INFO("Calling startup script: %s", bash_command.c_str());
+	PX4_INFO("Calling startup script: %s", shell_command.c_str());
 
 	int ret = 0;
 
-	if (!bash_command.empty()) {
-		ret = system(bash_command.c_str());
+	if (!shell_command.empty()) {
+		ret = system(shell_command.c_str());
 
 		if (ret == 0) {
 			PX4_INFO("Startup script returned successfully");
@@ -560,7 +555,7 @@ void print_usage()
 	printf("\n");
 	printf("    px4 [-h|-d] [-s <startup_file>] [-t <test_data_directory>] [<rootfs_directory>] [-i <instance>]\n");
 	printf("\n");
-	printf("    -s <startup_file>  bash start script to be used as startup (default=etc/init.d/rcS)\n");
+	printf("    -s <startup_file>  shell script to be used as startup (default=etc/init.d/rcS)\n");
 	printf("    <rootfs_directory> directory where startup files and mixers are located,\n");
 	printf("                       (if not given, CWD is used)\n");
 	printf("    -i <instance>      px4 instance id to run multiple instances [0...N], default=0\n");

platforms/posix/src/px4-alias.sh_in

@@ -2,14 +2,9 @@
 
 # File is auto-generated by cmake compilation, do not edit.
 
-# Ignore the expand_aliases command in zshell.
-if [ ! -n "$ZSH_VERSION" ]; then
-	shopt -s expand_aliases
-fi
-
 # Map the NuttX-style variable definition 'set <var> <value>' to something that
 # bash and alternatives understand
-# define _set first because sh does not like overwriting set directly
+# define _set first because sh (POSIX shell) does not like overwriting set directly
 _set() {
 	eval $1=$2
 }
@@ -22,8 +17,15 @@ alias set=_set
 # scripts)
 sh() {
 	script="$1"
-	[[ "$script" != /* ]] && script="/$script"
-	source "$(pwd)$script"
+	case "$script" in
+	"/"*)
+		script="$script"
+		;;
+	*)
+		script="/$script"
+		;;
+	esac
+	. "$(pwd)$script"
 }
 
 # Don't stop on errors.
@@ -32,6 +34,6 @@ sh() {
 # Arguments passed to this script:
 # $1: optional instance id
 px4_instance=0
-[[ -n "$1" ]] && px4_instance=$1
+[ -n "$1" ] && px4_instance=$1
 
 ${alias_string}