diff --git a/src/builtin.cpp b/src/builtin.cpp
index 686dfbace..c660defe2 100644
--- a/src/builtin.cpp
+++ b/src/builtin.cpp
@@ -119,8 +119,8 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {nullptr, 0, nullptr, 0}};
 
 int parse_help_only_cmd_opts(struct help_only_cmd_opts_t &opts, int *optind, int argc,
-                             wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                             const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -204,7 +204,7 @@ void builtin_print_error_trailer(parser_t &parser, output_stream_t &b, const wch
 
 /// A generic bultin that only supports showing a help message. This is only a placeholder that
 /// prints the help message. Useful for commands that live in the parser.
-static maybe_t<int> builtin_generic(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+static maybe_t<int> builtin_generic(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
@@ -231,7 +231,7 @@ static maybe_t<int> builtin_generic(parser_t &parser, io_streams_t &streams, wch
 // Since this is just for counting, it can be massive.
 #define COUNT_CHUNK_SIZE (512 * 256)
 /// Implementation of the builtin count command, used to count the number of arguments sent to it.
-static maybe_t<int> builtin_count(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+static maybe_t<int> builtin_count(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     int argc = 0;
 
@@ -266,7 +266,7 @@ static maybe_t<int> builtin_count(parser_t &parser, io_streams_t &streams, wchar
 /// This function handles both the 'continue' and the 'break' builtins that are used for loop
 /// control.
 static maybe_t<int> builtin_break_continue(parser_t &parser, io_streams_t &streams,
-                                           wchar_t **argv) {
+                                           const wchar_t **argv) {
     int is_break = (std::wcscmp(argv[0], L"break") == 0);
     int argc = builtin_count_args(argv);
 
@@ -297,8 +297,9 @@ static maybe_t<int> builtin_break_continue(parser_t &parser, io_streams_t &strea
 }
 
 /// Implementation of the builtin breakpoint command, used to launch the interactive debugger.
-static maybe_t<int> builtin_breakpoint(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+static maybe_t<int> builtin_breakpoint(parser_t &parser, io_streams_t &streams,
+                                       const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     if (argv[1] != nullptr) {
         streams.err.append_format(BUILTIN_ERR_ARG_COUNT1, cmd, 0, builtin_count_args(argv) - 1);
         return STATUS_INVALID_ARGS;
@@ -323,21 +324,21 @@ static maybe_t<int> builtin_breakpoint(parser_t &parser, io_streams_t &streams,
     return parser.get_last_status();
 }
 
-maybe_t<int> builtin_true(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_true(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     UNUSED(streams);
     UNUSED(argv);
     return STATUS_CMD_OK;
 }
 
-maybe_t<int> builtin_false(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_false(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     UNUSED(streams);
     UNUSED(argv);
     return STATUS_CMD_ERROR;
 }
 
-maybe_t<int> builtin_gettext(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_gettext(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     UNUSED(streams);
     for (int i = 1; i < builtin_count_args(argv); i++) {
@@ -455,7 +456,7 @@ static const wchar_t *const help_builtins[] = {L"for", L"while",  L"function", L
 static bool cmd_needs_help(const wchar_t *cmd) { return contains(help_builtins, cmd); }
 
 /// Execute a builtin command
-proc_status_t builtin_run(parser_t &parser, wchar_t **argv, io_streams_t &streams) {
+proc_status_t builtin_run(parser_t &parser, const wchar_t **argv, io_streams_t &streams) {
     UNUSED(parser);
     UNUSED(streams);
     if (argv == nullptr || argv[0] == nullptr)
diff --git a/src/builtin.h b/src/builtin.h
index 00b9ec6c6..fece694aa 100644
--- a/src/builtin.h
+++ b/src/builtin.h
@@ -20,7 +20,7 @@ struct builtin_data_t {
     // Name of the builtin.
     const wchar_t *name;
     // Function pointer to the builtin implementation.
-    maybe_t<int> (*func)(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+    maybe_t<int> (*func)(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
     // Description of what the builtin does.
     const wchar_t *desc;
 
@@ -85,7 +85,7 @@ enum { COMMAND_NOT_BUILTIN, BUILTIN_REGULAR, BUILTIN_FUNCTION };
 void builtin_init();
 bool builtin_exists(const wcstring &cmd);
 
-proc_status_t builtin_run(parser_t &parser, wchar_t **argv, io_streams_t &streams);
+proc_status_t builtin_run(parser_t &parser, const wchar_t **argv, io_streams_t &streams);
 
 wcstring_list_t builtin_get_names();
 void builtin_get_names(completion_list_t *list);
@@ -110,6 +110,6 @@ void builtin_wperror(const wchar_t *s, io_streams_t &streams);
 struct help_only_cmd_opts_t {
     bool print_help = false;
 };
-int parse_help_only_cmd_opts(help_only_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
-                             parser_t &parser, io_streams_t &streams);
+int parse_help_only_cmd_opts(help_only_cmd_opts_t &opts, int *optind, int argc,
+                             const wchar_t **argv, parser_t &parser, io_streams_t &streams);
 #endif
diff --git a/src/builtin_argparse.cpp b/src/builtin_argparse.cpp
index 289dbec75..b4facf9a4 100644
--- a/src/builtin_argparse.cpp
+++ b/src/builtin_argparse.cpp
@@ -321,9 +321,9 @@ static bool parse_option_spec(argparse_cmd_opts_t &opts,  //!OCLINT(high npath c
     return true;
 }
 
-static int collect_option_specs(argparse_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
-                                io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+static int collect_option_specs(argparse_cmd_opts_t &opts, int *optind, int argc,
+                                const wchar_t **argv, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
 
     // A counter to give short chars to long-only options because getopt needs that.
     // Luckily we have wgetopt so we can use wchars - this is one of the private use areas so we
@@ -360,8 +360,8 @@ static int collect_option_specs(argparse_cmd_opts_t &opts, int *optind, int argc
 }
 
 static int parse_cmd_opts(argparse_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -564,7 +564,7 @@ static int handle_flag(parser_t &parser, const argparse_cmd_opts_t &opts, option
 
 static int argparse_parse_flags(parser_t &parser, argparse_cmd_opts_t &opts,
                                 const wchar_t *short_options, const woption *long_options,
-                                const wchar_t *cmd, int argc, wchar_t **argv, int *optind,
+                                const wchar_t *cmd, int argc, const wchar_t **argv, int *optind,
                                 io_streams_t &streams) {
     int opt;
     int long_idx = -1;
@@ -704,7 +704,7 @@ static void set_argparse_result_vars(env_stack_t &vars, const argparse_cmd_opts_
 /// an external command also means its output has to be in a form that can be eval'd. Because our
 /// version is a builtin it can directly set variables local to the current scope (e.g., a
 /// function). It doesn't need to write anything to stdout that then needs to be eval'd.
-maybe_t<int> builtin_argparse(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_argparse(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     argparse_cmd_opts_t opts;
diff --git a/src/builtin_argparse.h b/src/builtin_argparse.h
index 24e4b6079..8d0422adc 100644
--- a/src/builtin_argparse.h
+++ b/src/builtin_argparse.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_argparse(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_argparse(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_bg.cpp b/src/builtin_bg.cpp
index 798d72511..d3ea75d0c 100644
--- a/src/builtin_bg.cpp
+++ b/src/builtin_bg.cpp
@@ -37,7 +37,7 @@ static int send_to_bg(parser_t &parser, io_streams_t &streams, job_t *j) {
 }
 
 /// Builtin for putting a job in the background.
-maybe_t<int> builtin_bg(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_bg(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_bg.h b/src/builtin_bg.h
index bb628a433..133c2cb57 100644
--- a/src/builtin_bg.h
+++ b/src/builtin_bg.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_bg(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_bg(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_bind.cpp b/src/builtin_bind.cpp
index 632097761..502464037 100644
--- a/src/builtin_bind.cpp
+++ b/src/builtin_bind.cpp
@@ -188,8 +188,8 @@ bool builtin_bind_t::add(const wcstring &seq, const wchar_t *const *cmds, size_t
 /// @param  use_terminfo
 ///    Whether to look use terminfo -k name
 ///
-bool builtin_bind_t::erase(wchar_t **seq, bool all, const wchar_t *mode, bool use_terminfo,
-                           bool user, io_streams_t &streams) {
+bool builtin_bind_t::erase(const wchar_t *const *seq, bool all, const wchar_t *mode,
+                           bool use_terminfo, bool user, io_streams_t &streams) {
     if (all) {
         input_mappings_->clear(mode, user);
         return false;
@@ -214,8 +214,8 @@ bool builtin_bind_t::erase(wchar_t **seq, bool all, const wchar_t *mode, bool us
     return res;
 }
 
-bool builtin_bind_t::insert(int optind, int argc, wchar_t **argv, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+bool builtin_bind_t::insert(int optind, int argc, const wchar_t **argv, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int arg_count = argc - optind;
 
     if (arg_count < 2) {
@@ -300,8 +300,8 @@ void builtin_bind_t::list_modes(io_streams_t &streams) {
 }
 
 static int parse_cmd_opts(bind_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     static const wchar_t *const short_options = L":aehkKfM:Lm:s";
     static const struct woption long_options[] = {{L"all", no_argument, nullptr, 'a'},
                                                   {L"erase", no_argument, nullptr, 'e'},
@@ -399,8 +399,9 @@ static int parse_cmd_opts(bind_cmd_opts_t &opts, int *optind,  //!OCLINT(high nc
 }
 
 /// The bind builtin, used for setting character sequences.
-maybe_t<int> builtin_bind_t::builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_bind_t::builtin_bind(parser_t &parser, io_streams_t &streams,
+                                          const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     bind_cmd_opts_t opts;
     this->opts = &opts;
diff --git a/src/builtin_bind.h b/src/builtin_bind.h
index a6050f93e..26951564d 100644
--- a/src/builtin_bind.h
+++ b/src/builtin_bind.h
@@ -11,7 +11,7 @@ struct bind_cmd_opts_t;
 
 class builtin_bind_t {
    public:
-    maybe_t<int> builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+    maybe_t<int> builtin_bind(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 
     builtin_bind_t() : input_mappings_(input_mappings()) {}
 
@@ -28,17 +28,17 @@ class builtin_bind_t {
     void function_names(io_streams_t &streams);
     bool add(const wcstring &seq, const wchar_t *const *cmds, size_t cmds_len, const wchar_t *mode,
              const wchar_t *sets_mode, bool terminfo, bool user, io_streams_t &streams);
-    bool erase(wchar_t **seq, bool all, const wchar_t *mode, bool use_terminfo, bool user,
-               io_streams_t &streams);
+    bool erase(const wchar_t *const *seq, bool all, const wchar_t *mode, bool use_terminfo,
+               bool user, io_streams_t &streams);
     bool get_terminfo_sequence(const wcstring &seq, wcstring *out_seq, io_streams_t &streams) const;
-    bool insert(int optind, int argc, wchar_t **argv, io_streams_t &streams);
+    bool insert(int optind, int argc, const wchar_t **argv, io_streams_t &streams);
     void list_modes(io_streams_t &streams);
     bool list_one(const wcstring &seq, const wcstring &bind_mode, bool user, io_streams_t &streams);
     bool list_one(const wcstring &seq, const wcstring &bind_mode, bool user, bool preset,
                   io_streams_t &streams);
 };
 
-inline maybe_t<int> builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+inline maybe_t<int> builtin_bind(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     builtin_bind_t bind;
     return bind.builtin_bind(parser, streams, argv);
 }
diff --git a/src/builtin_block.cpp b/src/builtin_block.cpp
index e2e9b78d8..6b9491a5c 100644
--- a/src/builtin_block.cpp
+++ b/src/builtin_block.cpp
@@ -22,8 +22,8 @@ struct block_cmd_opts_t {
 };
 
 static int parse_cmd_opts(block_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     static const wchar_t *const short_options = L":eghl";
     static const struct woption long_options[] = {{L"erase", no_argument, nullptr, 'e'},
                                                   {L"local", no_argument, nullptr, 'l'},
@@ -70,7 +70,7 @@ static int parse_cmd_opts(block_cmd_opts_t &opts, int *optind,  //!OCLINT(high n
 }
 
 /// The block builtin, used for temporarily blocking events.
-maybe_t<int> builtin_block(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_block(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     block_cmd_opts_t opts;
diff --git a/src/builtin_block.h b/src/builtin_block.h
index 96cf844cf..5b7b4234b 100644
--- a/src/builtin_block.h
+++ b/src/builtin_block.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_block(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_block(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_builtin.cpp b/src/builtin_builtin.cpp
index 30d291274..7096a6cdd 100644
--- a/src/builtin_builtin.cpp
+++ b/src/builtin_builtin.cpp
@@ -25,9 +25,9 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {L"query", no_argument, nullptr, 'q'},
                                               {nullptr, 0, nullptr, 0}};
 
-static int parse_cmd_opts(builtin_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
+static int parse_cmd_opts(builtin_cmd_opts_t &opts, int *optind, int argc, const wchar_t **argv,
                           parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -65,7 +65,7 @@ static int parse_cmd_opts(builtin_cmd_opts_t &opts, int *optind, int argc, wchar
 /// The builtin builtin, used for giving builtins precedence over functions. Mostly handled by the
 /// parser. All this code does is some additional operational modes, such as printing a list of all
 /// builtins, printing help, etc.
-maybe_t<int> builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_builtin(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     builtin_cmd_opts_t opts;
diff --git a/src/builtin_builtin.h b/src/builtin_builtin.h
index 75e5ccc4c..ec247fcac 100644
--- a/src/builtin_builtin.h
+++ b/src/builtin_builtin.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_builtin(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_cd.cpp b/src/builtin_cd.cpp
index ccdd01958..880a5e522 100644
--- a/src/builtin_cd.cpp
+++ b/src/builtin_cd.cpp
@@ -20,7 +20,7 @@
 
 /// The cd builtin. Changes the current directory to the one specified or to $HOME if none is
 /// specified. The directory can be relative to any directory in the CDPATH variable.
-maybe_t<int> builtin_cd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_cd(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_cd.h b/src/builtin_cd.h
index a28a85f4c..26070e6c7 100644
--- a/src/builtin_cd.h
+++ b/src/builtin_cd.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_cd(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_cd(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_command.cpp b/src/builtin_command.cpp
index e42093edf..53d826a3c 100644
--- a/src/builtin_command.cpp
+++ b/src/builtin_command.cpp
@@ -28,9 +28,9 @@ static const struct woption long_options[] = {
     {L"quiet", no_argument, nullptr, 'q'},  {L"query", no_argument, nullptr, 'q'},
     {L"search", no_argument, nullptr, 's'}, {nullptr, 0, nullptr, 0}};
 
-static int parse_cmd_opts(command_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
+static int parse_cmd_opts(command_cmd_opts_t &opts, int *optind, int argc, const wchar_t **argv,
                           parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -72,7 +72,7 @@ static int parse_cmd_opts(command_cmd_opts_t &opts, int *optind, int argc, wchar
 
 /// Implementation of the builtin 'command'. Actual command running is handled by the parser, this
 /// just processes the flags.
-maybe_t<int> builtin_command(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_command(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     command_cmd_opts_t opts;
diff --git a/src/builtin_command.h b/src/builtin_command.h
index 8557bc13d..84c7a7672 100644
--- a/src/builtin_command.h
+++ b/src/builtin_command.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_command(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_command(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_commandline.cpp b/src/builtin_commandline.cpp
index da4c4afdc..888026bef 100644
--- a/src/builtin_commandline.cpp
+++ b/src/builtin_commandline.cpp
@@ -124,7 +124,7 @@ static void write_part(const wchar_t *begin, const wchar_t *end, int cut_at_curs
 }
 
 /// The commandline builtin. It is used for specifying a new value for the commandline.
-maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     // Pointer to what the commandline builtin considers to be the current contents of the command
     // line buffer.
     const wchar_t *current_buffer = nullptr;
@@ -132,7 +132,7 @@ maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_
     // What the commandline builtin considers to be the current cursor position.
     auto current_cursor_pos = static_cast<size_t>(-1);
 
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int buffer_part = 0;
     bool cut_at_cursor = false;
 
diff --git a/src/builtin_commandline.h b/src/builtin_commandline.h
index 277056ae5..8b4d3d31d 100644
--- a/src/builtin_commandline.h
+++ b/src/builtin_commandline.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_complete.cpp b/src/builtin_complete.cpp
index 72b1571ea..a063775d1 100644
--- a/src/builtin_complete.cpp
+++ b/src/builtin_complete.cpp
@@ -123,10 +123,10 @@ static void builtin_complete_print(const wcstring &cmd, io_streams_t &streams, p
 
 /// The complete builtin. Used for specifying programmable tab-completions. Calls the functions in
 // complete.cpp for any heavy lifting.
-maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     ASSERT_IS_MAIN_THREAD();
 
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     completion_mode_t result_mode{};
     int remove = 0;
diff --git a/src/builtin_complete.h b/src/builtin_complete.h
index c2f3ab31b..bb7097f49 100644
--- a/src/builtin_complete.h
+++ b/src/builtin_complete.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_contains.cpp b/src/builtin_contains.cpp
index 389ad0916..ad91667f7 100644
--- a/src/builtin_contains.cpp
+++ b/src/builtin_contains.cpp
@@ -23,9 +23,9 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {L"index", no_argument, nullptr, 'i'},
                                               {nullptr, 0, nullptr, 0}};
 
-static int parse_cmd_opts(contains_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
+static int parse_cmd_opts(contains_cmd_opts_t &opts, int *optind, int argc, const wchar_t **argv,
                           parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -58,7 +58,7 @@ static int parse_cmd_opts(contains_cmd_opts_t &opts, int *optind, int argc, wcha
 
 /// Implementation of the builtin contains command, used to check if a specified string is part of
 /// a list.
-maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     contains_cmd_opts_t opts;
@@ -72,7 +72,7 @@ maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t *
         return STATUS_CMD_OK;
     }
 
-    wchar_t *needle = argv[optind];
+    const wchar_t *needle = argv[optind];
     if (!needle) {
         streams.err.append_format(_(L"%ls: Key not specified\n"), cmd);
     } else {
diff --git a/src/builtin_contains.h b/src/builtin_contains.h
index fca65875c..96f00ded1 100644
--- a/src/builtin_contains.h
+++ b/src/builtin_contains.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_disown.cpp b/src/builtin_disown.cpp
index cfccefa7a..b6ff9c9cb 100644
--- a/src/builtin_disown.cpp
+++ b/src/builtin_disown.cpp
@@ -42,7 +42,7 @@ static int disown_job(const wchar_t *cmd, parser_t &parser, io_streams_t &stream
 }
 
 /// Builtin for removing jobs from the job list.
-maybe_t<int> builtin_disown(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_disown(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_disown.h b/src/builtin_disown.h
index d6c836928..d0eb2debe 100644
--- a/src/builtin_disown.h
+++ b/src/builtin_disown.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_disown(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_disown(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_echo.cpp b/src/builtin_echo.cpp
index e380f63ed..12ed26c19 100644
--- a/src/builtin_echo.cpp
+++ b/src/builtin_echo.cpp
@@ -21,11 +21,11 @@ struct echo_cmd_opts_t {
 static const wchar_t *const short_options = L"+:Eens";
 static const struct woption *const long_options = nullptr;
 
-static int parse_cmd_opts(echo_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
+static int parse_cmd_opts(echo_cmd_opts_t &opts, int *optind, int argc, const wchar_t **argv,
                           parser_t &parser, io_streams_t &streams) {
     UNUSED(parser);
     UNUSED(streams);
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     echo_cmd_opts_t oldopts = opts;
@@ -194,8 +194,8 @@ static bool builtin_echo_parse_numeric_sequence(const wchar_t *str, size_t *cons
 ///
 /// Bash only respects -n if it's the first argument. We'll do the same. We also support a new,
 /// fish specific, option -s to mean "no spaces".
-maybe_t<int> builtin_echo(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_echo(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     UNUSED(cmd);
     int argc = builtin_count_args(argv);
     echo_cmd_opts_t opts;
diff --git a/src/builtin_echo.h b/src/builtin_echo.h
index 612e869a7..7b9d0ba1a 100644
--- a/src/builtin_echo.h
+++ b/src/builtin_echo.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_echo(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_echo(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_emit.cpp b/src/builtin_emit.cpp
index 161d652a0..97ad03767 100644
--- a/src/builtin_emit.cpp
+++ b/src/builtin_emit.cpp
@@ -11,7 +11,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Implementation of the builtin emit command, used to create events.
-maybe_t<int> builtin_emit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_emit(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_emit.h b/src/builtin_emit.h
index 6ca671d88..fc1b06e8c 100644
--- a/src/builtin_emit.h
+++ b/src/builtin_emit.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_emit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_emit(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_eval.cpp b/src/builtin_eval.cpp
index 19a09d2b3..bd95e1390 100644
--- a/src/builtin_eval.cpp
+++ b/src/builtin_eval.cpp
@@ -15,7 +15,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Implementation of eval builtin.
-maybe_t<int> builtin_eval(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_eval(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     int argc = builtin_count_args(argv);
     if (argc <= 1) {
         return STATUS_CMD_OK;
diff --git a/src/builtin_eval.h b/src/builtin_eval.h
index ae67c7da9..128671b4d 100644
--- a/src/builtin_eval.h
+++ b/src/builtin_eval.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_eval(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_eval(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_exit.cpp b/src/builtin_exit.cpp
index 4a28265d5..c1a400fb7 100644
--- a/src/builtin_exit.cpp
+++ b/src/builtin_exit.cpp
@@ -24,10 +24,10 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(exit_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     UNUSED(parser);
     UNUSED(streams);
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -58,7 +58,7 @@ static int parse_cmd_opts(exit_cmd_opts_t &opts, int *optind,  //!OCLINT(high nc
 }
 
 /// The exit builtin. Calls reader_exit to exit and returns the value specified.
-maybe_t<int> builtin_exit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_exit(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     exit_cmd_opts_t opts;
diff --git a/src/builtin_exit.h b/src/builtin_exit.h
index f446daddf..91822b9a5 100644
--- a/src/builtin_exit.h
+++ b/src/builtin_exit.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_exit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_exit(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_fg.cpp b/src/builtin_fg.cpp
index 1211c27c1..19f155f54 100644
--- a/src/builtin_fg.cpp
+++ b/src/builtin_fg.cpp
@@ -21,7 +21,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Builtin for putting a job in the foreground.
-maybe_t<int> builtin_fg(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_fg(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_fg.h b/src/builtin_fg.h
index 8503f7286..713c431b1 100644
--- a/src/builtin_fg.h
+++ b/src/builtin_fg.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_fg(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_fg(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_function.cpp b/src/builtin_function.cpp
index 5d9590c67..9e09be99d 100644
--- a/src/builtin_function.cpp
+++ b/src/builtin_function.cpp
@@ -54,7 +54,7 @@ static const struct woption long_options[] = {
     {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(function_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     const wchar_t *cmd = L"function";
     int opt;
     wgetopter_t w;
@@ -210,8 +210,8 @@ maybe_t<int> builtin_function(parser_t &parser, io_streams_t &streams,
     args.insert(args.end(), c_args.begin(), c_args.end());
 
     null_terminated_array_t<wchar_t> argv_array(args);
-    wchar_t **argv = argv_array.get();
-    wchar_t *cmd = argv[0];
+    const wchar_t **argv = argv_array.get();
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
 
     // A valid function name has to be the first argument.
diff --git a/src/builtin_functions.cpp b/src/builtin_functions.cpp
index e65d4ab43..5b8bf8985 100644
--- a/src/builtin_functions.cpp
+++ b/src/builtin_functions.cpp
@@ -42,8 +42,8 @@ struct functions_cmd_opts_t {
     bool report_metadata = false;
     bool verbose = false;
     bool handlers = false;
-    wchar_t *handlers_type = nullptr;
-    wchar_t *description = nullptr;
+    const wchar_t *handlers_type = nullptr;
+    const wchar_t *description = nullptr;
 };
 static const wchar_t *const short_options = L":Ht:Dacd:ehnqv";
 static const struct woption long_options[] = {{L"erase", no_argument, nullptr, 'e'},
@@ -60,8 +60,8 @@ static const struct woption long_options[] = {{L"erase", no_argument, nullptr, '
                                               {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(functions_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -184,7 +184,7 @@ static int report_function_metadata(const wchar_t *funcname, bool verbose, io_st
 }
 
 /// The functions builtin, used for listing and erasing functions.
-maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     functions_cmd_opts_t opts;
@@ -212,15 +212,13 @@ maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t
     }
 
     if (opts.description) {
-        wchar_t *func;
-
         if (argc - optind != 1) {
             streams.err.append_format(_(L"%ls: Expected exactly one function name\n"), cmd);
             builtin_print_error_trailer(parser, streams.err, cmd);
             return STATUS_INVALID_ARGS;
         }
 
-        func = argv[optind];
+        const wchar_t *func = argv[optind];
         if (!function_exists(func, parser)) {
             streams.err.append_format(_(L"%ls: Function '%ls' does not exist\n"), cmd, func);
             builtin_print_error_trailer(parser, streams.err, cmd);
diff --git a/src/builtin_functions.h b/src/builtin_functions.h
index 1746eaac3..3378d50ed 100644
--- a/src/builtin_functions.h
+++ b/src/builtin_functions.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_history.cpp b/src/builtin_history.cpp
index 5dffd9e98..2f8cde9de 100644
--- a/src/builtin_history.cpp
+++ b/src/builtin_history.cpp
@@ -61,7 +61,7 @@ static const struct woption long_options[] = {{L"prefix", no_argument, nullptr,
                                               {nullptr, 0, nullptr, 0}};
 
 /// Remember the history subcommand and disallow selecting more than one history subcommand.
-static bool set_hist_cmd(wchar_t *const cmd, hist_cmd_t *hist_cmd, hist_cmd_t sub_cmd,
+static bool set_hist_cmd(const wchar_t *cmd, hist_cmd_t *hist_cmd, hist_cmd_t sub_cmd,
                          io_streams_t &streams) {
     if (*hist_cmd != HIST_UNDEF) {
         wchar_t err_text[1024];
@@ -95,8 +95,8 @@ static bool check_for_unexpected_hist_args(const history_cmd_opts_t &opts, const
 }
 
 static int parse_cmd_opts(history_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -200,8 +200,8 @@ static int parse_cmd_opts(history_cmd_opts_t &opts, int *optind,  //!OCLINT(high
 }
 
 /// Manipulate history of interactive commands executed by the user.
-maybe_t<int> builtin_history(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_history(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     history_cmd_opts_t opts;
 
diff --git a/src/builtin_history.h b/src/builtin_history.h
index 3aef6aacd..7ab35a04f 100644
--- a/src/builtin_history.h
+++ b/src/builtin_history.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_history(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_history(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_jobs.cpp b/src/builtin_jobs.cpp
index e10b12d6d..6f9f86d56 100644
--- a/src/builtin_jobs.cpp
+++ b/src/builtin_jobs.cpp
@@ -121,8 +121,8 @@ static void builtin_jobs_print(const job_t *j, int mode, int header, io_streams_
 }
 
 /// The jobs builtin. Used for printing running jobs. Defined in builtin_jobs.c.
-maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     bool found = false;
     int mode = JOBS_DEFAULT;
diff --git a/src/builtin_jobs.h b/src/builtin_jobs.h
index a92375573..5d4f1e0a8 100644
--- a/src/builtin_jobs.h
+++ b/src/builtin_jobs.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_math.cpp b/src/builtin_math.cpp
index 310d2e554..9c43bc6a7 100644
--- a/src/builtin_math.cpp
+++ b/src/builtin_math.cpp
@@ -43,7 +43,7 @@ static const struct woption long_options[] = {{L"scale", required_argument, null
                                               {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(math_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     const wchar_t *cmd = L"math";
     int opt;
     wgetopter_t w;
@@ -140,13 +140,13 @@ static const wchar_t *math_get_arg_stdin(wcstring *storage, const io_streams_t &
 }
 
 /// Return the next argument from argv.
-static const wchar_t *math_get_arg_argv(int *argidx, wchar_t **argv) {
+static const wchar_t *math_get_arg_argv(int *argidx, const wchar_t **argv) {
     return argv && argv[*argidx] ? argv[(*argidx)++] : nullptr;
 }
 
 /// Get the arguments from argv or stdin based on the execution context. This mimics how builtin
 /// `string` does it.
-static const wchar_t *math_get_arg(int *argidx, wchar_t **argv, wcstring *storage,
+static const wchar_t *math_get_arg(int *argidx, const wchar_t **argv, wcstring *storage,
                                    const io_streams_t &streams) {
     if (math_args_from_stdin(streams)) {
         assert(streams.stdin_fd >= 0 &&
@@ -272,8 +272,8 @@ static int evaluate_expression(const wchar_t *cmd, const parser_t &parser, io_st
 }
 
 /// The math builtin evaluates math expressions.
-maybe_t<int> builtin_math(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_math(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     math_cmd_opts_t opts;
     int optind;
diff --git a/src/builtin_math.h b/src/builtin_math.h
index 80ef56702..7b2566d6a 100644
--- a/src/builtin_math.h
+++ b/src/builtin_math.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_math(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_math(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_printf.cpp b/src/builtin_printf.cpp
index 61cef9fcd..90fa3a116 100644
--- a/src/builtin_printf.cpp
+++ b/src/builtin_printf.cpp
@@ -90,7 +90,7 @@ struct builtin_printf_state_t {
     void print_direc(const wchar_t *start, size_t length, wchar_t conversion, bool have_field_width,
                      int field_width, bool have_precision, int precision, wchar_t const *argument);
 
-    int print_formatted(const wchar_t *format, int argc, wchar_t **argv);
+    int print_formatted(const wchar_t *format, int argc, const wchar_t **argv);
 
     void nonfatal_error(const wchar_t *fmt, ...);
     void fatal_error(const wchar_t *fmt, ...);
@@ -585,7 +585,7 @@ static inline void modify_allowed_format_specifiers(bool ok[UCHAR_MAX + 1], cons
 
 /// Print the text in FORMAT, using ARGV (with ARGC elements) for arguments to any `%' directives.
 /// Return the number of elements of ARGV used.
-int builtin_printf_state_t::print_formatted(const wchar_t *format, int argc, wchar_t **argv) {
+int builtin_printf_state_t::print_formatted(const wchar_t *format, int argc, const wchar_t **argv) {
     int save_argc = argc;        /* Preserve original value.  */
     const wchar_t *f;            /* Pointer into `format'.  */
     const wchar_t *direc_start;  /* Start of % directive.  */
@@ -737,7 +737,7 @@ int builtin_printf_state_t::print_formatted(const wchar_t *format, int argc, wch
 }
 
 /// The printf builtin.
-maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
@@ -759,7 +759,7 @@ maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **a
 
     builtin_printf_state_t state(streams);
     int args_used;
-    wchar_t *format = argv[0];
+    const wchar_t *format = argv[0];
     argc--;
     argv++;
 
diff --git a/src/builtin_printf.h b/src/builtin_printf.h
index 08be3e076..c724fde3d 100644
--- a/src/builtin_printf.h
+++ b/src/builtin_printf.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_pwd.cpp b/src/builtin_pwd.cpp
index 907a04fdf..80c8e579e 100644
--- a/src/builtin_pwd.cpp
+++ b/src/builtin_pwd.cpp
@@ -19,7 +19,7 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {L"logical", no_argument, nullptr, 'L'},
                                               {L"physical", no_argument, nullptr, 'P'},
                                               {nullptr, 0, nullptr, 0}};
-maybe_t<int> builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_pwd(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_pwd.h b/src/builtin_pwd.h
index 5e7b392fa..7b90b4156 100644
--- a/src/builtin_pwd.h
+++ b/src/builtin_pwd.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_pwd(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_random.cpp b/src/builtin_random.cpp
index 88e4c431a..8b38694ec 100644
--- a/src/builtin_random.cpp
+++ b/src/builtin_random.cpp
@@ -27,8 +27,8 @@ static std::minstd_rand get_seeded_engine() {
 }
 
 /// The random builtin generates random numbers.
-maybe_t<int> builtin_random(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_random(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
 
diff --git a/src/builtin_random.h b/src/builtin_random.h
index 80fd5b3f7..bf852824f 100644
--- a/src/builtin_random.h
+++ b/src/builtin_random.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_random(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_random(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_read.cpp b/src/builtin_read.cpp
index 6b9707375..f76c2ad60 100644
--- a/src/builtin_read.cpp
+++ b/src/builtin_read.cpp
@@ -80,8 +80,8 @@ static const struct woption long_options[] = {{L"array", no_argument, nullptr, '
                                               {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(read_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -434,8 +434,8 @@ static int validate_read_args(const wchar_t *cmd, read_cmd_opts_t &opts, int arg
 }
 
 /// The read builtin. Reads from stdin and stores the values in environment variables.
-maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     wcstring buff;
     int exit_res = STATUS_CMD_OK;
@@ -475,7 +475,7 @@ maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **arg
         opts.shell = false;
     }
 
-    wchar_t *const *var_ptr = argv;
+    const wchar_t *const *var_ptr = argv;
     auto vars_left = [&]() { return argv + argc - var_ptr; };
     auto clear_remaining_vars = [&]() {
         while (vars_left()) {
diff --git a/src/builtin_read.h b/src/builtin_read.h
index f1fdccdee..3093a12af 100644
--- a/src/builtin_read.h
+++ b/src/builtin_read.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_realpath.cpp b/src/builtin_realpath.cpp
index 1268e4e73..d91d9fff4 100644
--- a/src/builtin_realpath.cpp
+++ b/src/builtin_realpath.cpp
@@ -27,7 +27,7 @@ static const struct woption long_options[] = {{L"no-symlinks", no_argument, null
                                               {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(realpath_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
@@ -61,7 +61,7 @@ static int parse_cmd_opts(realpath_cmd_opts_t &opts, int *optind,  //!OCLINT(hig
 /// An implementation of the external realpath command. Doesn't support any options.
 /// In general scripts shouldn't invoke this directly. They should just use `realpath` which
 /// will fallback to this builtin if an external command cannot be found.
-maybe_t<int> builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_realpath(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     realpath_cmd_opts_t opts;
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_realpath.h b/src/builtin_realpath.h
index 2022e9d29..70d6088db 100644
--- a/src/builtin_realpath.h
+++ b/src/builtin_realpath.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_realpath(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_return.cpp b/src/builtin_return.cpp
index 5f521960d..181711eb9 100644
--- a/src/builtin_return.cpp
+++ b/src/builtin_return.cpp
@@ -23,10 +23,10 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {nullptr, 0, nullptr, 0}};
 
 static int parse_cmd_opts(return_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     UNUSED(parser);
     UNUSED(streams);
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -57,7 +57,7 @@ static int parse_cmd_opts(return_cmd_opts_t &opts, int *optind,  //!OCLINT(high
 }
 
 /// Function for handling the return builtin.
-maybe_t<int> builtin_return(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_return(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     return_cmd_opts_t opts;
diff --git a/src/builtin_return.h b/src/builtin_return.h
index 401ed6ec0..f43c33f71 100644
--- a/src/builtin_return.h
+++ b/src/builtin_return.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_return(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_return(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_set.cpp b/src/builtin_set.cpp
index d1c3737e5..32c59d03a 100644
--- a/src/builtin_set.cpp
+++ b/src/builtin_set.cpp
@@ -81,8 +81,8 @@ static const struct woption long_options[] = {
 static int is_path_variable(const wcstring &env) { return env == L"PATH" || env == L"CDPATH"; }
 
 static int parse_cmd_opts(set_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
 
     int opt;
     wgetopter_t w;
@@ -470,8 +470,8 @@ static env_mode_flags_t compute_scope(const set_cmd_opts_t &opts) {
 
 /// Print the names of all environment variables in the scope. It will include the values unless the
 /// `set --names` flag was used.
-static int builtin_set_list(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, wchar_t **argv,
-                            parser_t &parser, io_streams_t &streams) {
+static int builtin_set_list(const wchar_t *cmd, set_cmd_opts_t &opts, int argc,
+                            const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     UNUSED(cmd);
     UNUSED(argc);
     UNUSED(argv);
@@ -520,8 +520,8 @@ static int builtin_set_list(const wchar_t *cmd, set_cmd_opts_t &opts, int argc,
 }
 
 // Query mode. Return the number of variables that do NOT exist out of the specified variables.
-static int builtin_set_query(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, wchar_t **argv,
-                             parser_t &parser, io_streams_t &streams) {
+static int builtin_set_query(const wchar_t *cmd, set_cmd_opts_t &opts, int argc,
+                             const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     int retval = 0;
     env_mode_flags_t scope = compute_scope(opts);
 
@@ -596,7 +596,7 @@ static void show_scope(const wchar_t *var_name, int scope, io_streams_t &streams
 
 /// Show mode. Show information about the named variable(s).
 static int builtin_set_show(const wchar_t *cmd, const set_cmd_opts_t &opts, int argc,
-                            wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+                            const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     UNUSED(opts);
     const auto &vars = parser.vars();
     if (argc == 0) {  // show all vars
@@ -610,7 +610,7 @@ static int builtin_set_show(const wchar_t *cmd, const set_cmd_opts_t &opts, int
         }
     } else {
         for (int i = 0; i < argc; i++) {
-            wchar_t *arg = argv[i];
+            const wchar_t *arg = argv[i];
 
             if (!valid_var_name(arg)) {
                 streams.err.append_format(BUILTIN_ERR_VARNAME, cmd, arg);
@@ -635,8 +635,8 @@ static int builtin_set_show(const wchar_t *cmd, const set_cmd_opts_t &opts, int
 }
 
 /// Erase a variable.
-static int builtin_set_erase(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, wchar_t **argv,
-                             parser_t &parser, io_streams_t &streams) {
+static int builtin_set_erase(const wchar_t *cmd, set_cmd_opts_t &opts, int argc,
+                             const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
     int ret = STATUS_CMD_OK;
     env_mode_flags_t scope = compute_scope(opts);
     for (int i = 0; i < argc; i++) {
@@ -745,7 +745,7 @@ static wcstring_list_t new_var_values_by_index(const split_var_t &split, int arg
 }
 
 /// Set a variable.
-static int builtin_set_set(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, wchar_t **argv,
+static int builtin_set_set(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, const wchar_t **argv,
                            parser_t &parser, io_streams_t &streams) {
     if (argc == 0) {
         streams.err.append_format(BUILTIN_ERR_MIN_ARG_COUNT1, cmd, 1);
@@ -819,8 +819,8 @@ static int builtin_set_set(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, w
 }
 
 /// The set builtin creates, updates, and erases (removes, deletes) variables.
-maybe_t<int> builtin_set(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_set(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     set_cmd_opts_t opts;
 
diff --git a/src/builtin_set.h b/src/builtin_set.h
index 04c4877cd..e7ea6ddd8 100644
--- a/src/builtin_set.h
+++ b/src/builtin_set.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_set(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_set(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_set_color.cpp b/src/builtin_set_color.cpp
index f8f54f4de..073929ceb 100644
--- a/src/builtin_set_color.cpp
+++ b/src/builtin_set_color.cpp
@@ -105,7 +105,7 @@ static char dim_esc[] = "\x1B[2m";
 #endif
 
 /// set_color builtin.
-maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     // By the time this is called we should have initialized the curses subsystem.
     assert(curses_initialized);
 
diff --git a/src/builtin_set_color.h b/src/builtin_set_color.h
index 06be7db91..1a8dd0cce 100644
--- a/src/builtin_set_color.h
+++ b/src/builtin_set_color.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_source.cpp b/src/builtin_source.cpp
index 0fc73326a..2c2aa3c91 100644
--- a/src/builtin_source.cpp
+++ b/src/builtin_source.cpp
@@ -22,7 +22,7 @@
 
 /// The  source builtin, sometimes called `.`. Evaluates the contents of a file in the current
 /// context.
-maybe_t<int> builtin_source(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_source(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     ASSERT_IS_MAIN_THREAD();
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_source.h b/src/builtin_source.h
index e292727da..df6c6566d 100644
--- a/src/builtin_source.h
+++ b/src/builtin_source.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_source(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_source(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_status.cpp b/src/builtin_status.cpp
index ccb8200a5..8235527e1 100644
--- a/src/builtin_status.cpp
+++ b/src/builtin_status.cpp
@@ -82,7 +82,7 @@ const enum_map<status_cmd_t> status_enum_map[] = {
 /// Values that may be returned from the test-feature option to status.
 enum { TEST_FEATURE_ON, TEST_FEATURE_OFF, TEST_FEATURE_NOT_RECOGNIZED };
 
-static maybe_t<job_control_t> job_control_str_to_mode(const wchar_t *mode, wchar_t *cmd,
+static maybe_t<job_control_t> job_control_str_to_mode(const wchar_t *mode, const wchar_t *cmd,
                                                       io_streams_t &streams) {
     if (std::wcscmp(mode, L"full") == 0) {
         return job_control_t::all;
@@ -129,7 +129,7 @@ static const struct woption long_options[] = {
     {nullptr, 0, nullptr, 0}};
 
 /// Remember the status subcommand and disallow selecting more than one status subcommand.
-static bool set_status_cmd(wchar_t *const cmd, status_cmd_opts_t &opts, status_cmd_t sub_cmd,
+static bool set_status_cmd(const wchar_t *cmd, status_cmd_opts_t &opts, status_cmd_t sub_cmd,
                            io_streams_t &streams) {
     if (opts.status_cmd != STATUS_UNDEF) {
         wchar_t err_text[1024];
@@ -156,8 +156,8 @@ static void print_features(io_streams_t &streams) {
 }
 
 static int parse_cmd_opts(status_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss method)
-                          int argc, wchar_t **argv, parser_t &parser, io_streams_t &streams) {
-    wchar_t *cmd = argv[0];
+                          int argc, const wchar_t **argv, parser_t &parser, io_streams_t &streams) {
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -274,8 +274,8 @@ static int parse_cmd_opts(status_cmd_opts_t &opts, int *optind,  //!OCLINT(high
 }
 
 /// The status builtin. Gives various status information on fish.
-maybe_t<int> builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_status(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     status_cmd_opts_t opts;
 
diff --git a/src/builtin_status.h b/src/builtin_status.h
index 01855e120..72e4a4b1b 100644
--- a/src/builtin_status.h
+++ b/src/builtin_status.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_status(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_string.cpp b/src/builtin_string.cpp
index c0062f37a..e296bc6fc 100644
--- a/src/builtin_string.cpp
+++ b/src/builtin_string.cpp
@@ -197,7 +197,7 @@ struct options_t {  //!OCLINT(too many fields)
 };
 
 /// This handles the `--style=xxx` flag.
-static int handle_flag_1(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_1(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     const wchar_t *cmd = argv[0];
 
@@ -221,7 +221,7 @@ static int handle_flag_1(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_N(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_N(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->no_newline_valid) {
         opts->no_newline = true;
@@ -234,7 +234,7 @@ static int handle_flag_N(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_a(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_a(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->all_valid) {
         opts->all = true;
@@ -247,7 +247,7 @@ static int handle_flag_a(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_c(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_c(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->chars_to_trim_valid) {
         opts->chars_to_trim = w.woptarg;
@@ -265,7 +265,7 @@ static int handle_flag_c(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_e(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_e(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->end_valid) {
         opts->end = fish_wcstol(w.woptarg);
@@ -285,7 +285,7 @@ static int handle_flag_e(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_f(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_f(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->filter_valid) {
         opts->filter = true;
@@ -340,7 +340,7 @@ static int handle_flag_f(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_i(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_i(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->ignore_case_valid) {
         opts->ignore_case = true;
@@ -353,7 +353,7 @@ static int handle_flag_i(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_l(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_l(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->length_valid) {
         opts->length = fish_wcstol(w.woptarg);
@@ -373,7 +373,7 @@ static int handle_flag_l(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_m(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_m(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->max_valid) {
         opts->max = fish_wcstol(w.woptarg);
@@ -390,7 +390,7 @@ static int handle_flag_m(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_n(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_n(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->count_valid) {
         opts->count = fish_wcstol(w.woptarg);
@@ -416,7 +416,7 @@ static int handle_flag_n(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_q(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_q(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->quiet_valid) {
         opts->quiet = true;
@@ -426,7 +426,7 @@ static int handle_flag_q(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_r(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_r(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->regex_valid) {
         opts->regex = true;
@@ -439,7 +439,7 @@ static int handle_flag_r(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_s(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_s(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->start_valid) {
         opts->start = fish_wcstol(w.woptarg);
@@ -456,7 +456,7 @@ static int handle_flag_s(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_v(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_v(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     if (opts->invert_valid) {
         opts->invert_match = true;
@@ -466,7 +466,7 @@ static int handle_flag_v(wchar_t **argv, parser_t &parser, io_streams_t &streams
     return STATUS_INVALID_ARGS;
 }
 
-static int handle_flag_w(wchar_t **argv, parser_t &parser, io_streams_t &streams,
+static int handle_flag_w(const wchar_t **argv, parser_t &parser, io_streams_t &streams,
                          const wgetopter_t &w, options_t *opts) {
     long width = 0;
     if (opts->width_valid) {
@@ -553,7 +553,7 @@ static const std::unordered_map<char, decltype(*handle_flag_N)> flag_to_function
     {'v', handle_flag_v}, {'w', handle_flag_w}, {1, handle_flag_1}};
 
 /// Parse the arguments for flags recognized by a specific string subcommand.
-static int parse_opts(options_t *opts, int *optind, int n_req_args, int argc, wchar_t **argv,
+static int parse_opts(options_t *opts, int *optind, int n_req_args, int argc, const wchar_t **argv,
                       parser_t &parser, io_streams_t &streams) {
     const wchar_t *cmd = argv[0];
     wcstring short_opts = construct_short_opts(opts);
@@ -606,7 +606,7 @@ static int parse_opts(options_t *opts, int *optind, int n_req_args, int argc, wc
     return STATUS_CMD_OK;
 }
 
-static int string_escape(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_escape(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.no_quoted_valid = true;
     opts.style_valid = true;
@@ -634,7 +634,8 @@ static int string_escape(parser_t &parser, io_streams_t &streams, int argc, wcha
     DIE("should never reach this statement");
 }
 
-static int string_unescape(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_unescape(parser_t &parser, io_streams_t &streams, int argc,
+                           const wchar_t **argv) {
     options_t opts;
     opts.no_quoted_valid = true;
     opts.style_valid = true;
@@ -659,8 +660,8 @@ static int string_unescape(parser_t &parser, io_streams_t &streams, int argc, wc
     DIE("should never reach this statement");
 }
 
-static int string_join_maybe0(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv,
-                              bool is_join0) {
+static int string_join_maybe0(parser_t &parser, io_streams_t &streams, int argc,
+                              const wchar_t **argv, bool is_join0) {
     options_t opts;
     opts.quiet_valid = true;
     int optind;
@@ -688,15 +689,15 @@ static int string_join_maybe0(parser_t &parser, io_streams_t &streams, int argc,
     return nargs > 1 ? STATUS_CMD_OK : STATUS_CMD_ERROR;
 }
 
-static int string_join(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_join(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     return string_join_maybe0(parser, streams, argc, argv, false /* is_join0 */);
 }
 
-static int string_join0(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_join0(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     return string_join_maybe0(parser, streams, argc, argv, true /* is_join0 */);
 }
 
-static int string_length(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_length(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.quiet_valid = true;
     int optind;
@@ -1120,8 +1121,8 @@ class pcre2_matcher_t : public string_matcher_t {
     }
 };
 
-static int string_match(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+static int string_match(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
 
     options_t opts;
     opts.all_valid = true;
@@ -1160,7 +1161,7 @@ static int string_match(parser_t &parser, io_streams_t &streams, int argc, wchar
     return matcher->match_count() > 0 ? STATUS_CMD_OK : STATUS_CMD_ERROR;
 }
 
-static int string_pad(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_pad(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.char_to_pad_valid = true;
     opts.right_valid = true;
@@ -1384,7 +1385,7 @@ bool regex_replacer_t::replace_matches(const wcstring &arg) {
     return rc;
 }
 
-static int string_replace(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_replace(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.all_valid = true;
     opts.filter_valid = true;
@@ -1414,9 +1415,9 @@ static int string_replace(parser_t &parser, io_streams_t &streams, int argc, wch
     return replacer->replace_count() > 0 ? STATUS_CMD_OK : STATUS_CMD_ERROR;
 }
 
-static int string_split_maybe0(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv,
-                               bool is_split0) {
-    wchar_t *cmd = argv[0];
+static int string_split_maybe0(parser_t &parser, io_streams_t &streams, int argc,
+                               const wchar_t **argv, bool is_split0) {
+    const wchar_t *cmd = argv[0];
     options_t opts;
     opts.quiet_valid = true;
     opts.right_valid = true;
@@ -1502,15 +1503,15 @@ static int string_split_maybe0(parser_t &parser, io_streams_t &streams, int argc
     return split_count > arg_count ? STATUS_CMD_OK : STATUS_CMD_ERROR;
 }
 
-static int string_split(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_split(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     return string_split_maybe0(parser, streams, argc, argv, false /* is_split0 */);
 }
 
-static int string_split0(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_split0(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     return string_split_maybe0(parser, streams, argc, argv, true /* is_split0 */);
 }
 
-static int string_collect(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_collect(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.no_trim_newlines_valid = true;
     int optind;
@@ -1557,7 +1558,7 @@ static wcstring wcsrepeat_until(const wcstring &to_repeat, size_t max) {
     return wcsrepeat(to_repeat, count) + to_repeat.substr(0, mod);
 }
 
-static int string_repeat(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_repeat(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.count_valid = true;
     opts.max_valid = true;
@@ -1603,8 +1604,8 @@ static int string_repeat(parser_t &parser, io_streams_t &streams, int argc, wcha
     return all_empty ? STATUS_CMD_ERROR : STATUS_CMD_OK;
 }
 
-static int string_sub(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+static int string_sub(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
 
     options_t opts;
     opts.length_valid = true;
@@ -1667,7 +1668,7 @@ static int string_sub(parser_t &parser, io_streams_t &streams, int argc, wchar_t
     return nsub > 0 ? STATUS_CMD_OK : STATUS_CMD_ERROR;
 }
 
-static int string_trim(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_trim(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     options_t opts;
     opts.chars_to_trim_valid = true;
     opts.left_valid = true;
@@ -1711,7 +1712,7 @@ static int string_trim(parser_t &parser, io_streams_t &streams, int argc, wchar_
 }
 
 // A helper function for lower and upper.
-static int string_transform(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv,
+static int string_transform(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv,
                             std::wint_t (*func)(std::wint_t)) {
     options_t opts;
     opts.quiet_valid = true;
@@ -1737,12 +1738,12 @@ static int string_transform(parser_t &parser, io_streams_t &streams, int argc, w
 }
 
 /// Implementation of `string lower`.
-static int string_lower(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_lower(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     return string_transform(parser, streams, argc, argv, std::towlower);
 }
 
 /// Implementation of `string upper`.
-static int string_upper(parser_t &parser, io_streams_t &streams, int argc, wchar_t **argv) {
+static int string_upper(parser_t &parser, io_streams_t &streams, int argc, const wchar_t **argv) {
     return string_transform(parser, streams, argc, argv, std::towupper);
 }
 
@@ -1750,7 +1751,7 @@ static int string_upper(parser_t &parser, io_streams_t &streams, int argc, wchar
 static constexpr const struct string_subcommand {
     const wchar_t *name;
     int (*handler)(parser_t &, io_streams_t &, int argc,  //!OCLINT(unused param)
-                   wchar_t **argv);                       //!OCLINT(unused param)
+                   const wchar_t **argv);                 //!OCLINT(unused param)
 } string_subcommands[] = {
     {L"collect", &string_collect}, {L"escape", &string_escape}, {L"join", &string_join},
     {L"join0", &string_join0},     {L"length", &string_length}, {L"lower", &string_lower},
@@ -1762,8 +1763,8 @@ static constexpr const struct string_subcommand {
 ASSERT_SORT_ORDER(string_subcommands, .name);
 
 /// The string builtin, for manipulating strings.
-maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     if (argc <= 1) {
         streams.err.append_format(BUILTIN_ERR_MISSING_SUBCMD, cmd);
diff --git a/src/builtin_string.h b/src/builtin_string.h
index 47c5e1227..224873405 100644
--- a/src/builtin_string.h
+++ b/src/builtin_string.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_test.cpp b/src/builtin_test.cpp
index 38125ed89..4c8c416f2 100644
--- a/src/builtin_test.cpp
+++ b/src/builtin_test.cpp
@@ -209,7 +209,7 @@ class test_parser {
     unique_ptr<expression> parse_just_a_string(unsigned int start, unsigned int end);
 
     static unique_ptr<expression> parse_args(const wcstring_list_t &args, wcstring &err,
-                                             wchar_t *program_name);
+                                             const wchar_t *program_name);
 };
 
 struct range_t {
@@ -549,7 +549,7 @@ unique_ptr<expression> test_parser::parse_expression(unsigned int start, unsigne
 }
 
 unique_ptr<expression> test_parser::parse_args(const wcstring_list_t &args, wcstring &err,
-                                               wchar_t *program_name) {
+                                               const wchar_t *program_name) {
     // Empty list and one-arg list should be handled by caller.
     assert(args.size() > 1);
 
@@ -850,7 +850,7 @@ static bool unary_primary_evaluate(test_expressions::token_t token, const wcstri
 /// supports a more limited range of functionality.
 ///
 /// Return status is the final shell status, i.e. 0 for true, 1 for false and 2 for error.
-maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     using namespace test_expressions;
 
@@ -858,7 +858,7 @@ maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **arg
     if (!argv[0]) return STATUS_INVALID_ARGS;
 
     // Whether we are invoked with bracket '[' or not.
-    wchar_t *program_name = argv[0];
+    const wchar_t *program_name = argv[0];
     const bool is_bracket = !std::wcscmp(program_name, L"[");
 
     size_t argc = 0;
diff --git a/src/builtin_test.h b/src/builtin_test.h
index 8b8935e86..9fadeadbf 100644
--- a/src/builtin_test.h
+++ b/src/builtin_test.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_type.cpp b/src/builtin_type.cpp
index a5e03ab6c..18994b884 100644
--- a/src/builtin_type.cpp
+++ b/src/builtin_type.cpp
@@ -43,10 +43,10 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {L"quiet", no_argument, nullptr, 'q'},
                                               {nullptr, 0, nullptr, 0}};
 
-static int parse_cmd_opts(type_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
+static int parse_cmd_opts(type_cmd_opts_t &opts, int *optind, int argc, const wchar_t **argv,
                           parser_t &parser, io_streams_t &streams) {
     UNUSED(parser);
-    wchar_t *cmd = argv[0];
+    const wchar_t *cmd = argv[0];
     int opt;
     wgetopter_t w;
     while ((opt = w.wgetopt_long(argc, argv, short_options, long_options, nullptr)) != -1) {
@@ -102,7 +102,7 @@ static int parse_cmd_opts(type_cmd_opts_t &opts, int *optind, int argc, wchar_t
 }
 
 /// Implementation of the builtin 'type'.
-maybe_t<int> builtin_type(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_type(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     UNUSED(parser);
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_type.h b/src/builtin_type.h
index 99a32ba0a..93e98dc75 100644
--- a/src/builtin_type.h
+++ b/src/builtin_type.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_type(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_type(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_ulimit.cpp b/src/builtin_ulimit.cpp
index 72b114cfe..236c1bd5a 100644
--- a/src/builtin_ulimit.cpp
+++ b/src/builtin_ulimit.cpp
@@ -149,8 +149,8 @@ static int set_limit(int resource, int hard, int soft, rlim_t value, io_streams_
 }
 
 /// The ulimit builtin, used for setting resource limits.
-maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
-    wchar_t *cmd = argv[0];
+maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
+    const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     bool report_all = false;
     bool hard = false;
diff --git a/src/builtin_ulimit.h b/src/builtin_ulimit.h
index 1d64c39e4..a9d449d50 100644
--- a/src/builtin_ulimit.h
+++ b/src/builtin_ulimit.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/builtin_wait.cpp b/src/builtin_wait.cpp
index e450ffafc..e8a8a68fe 100644
--- a/src/builtin_wait.cpp
+++ b/src/builtin_wait.cpp
@@ -170,7 +170,7 @@ static bool find_job_by_name(const wchar_t *proc, std::vector<job_id_t> &ids,
     return found;
 }
 
-maybe_t<int> builtin_wait(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_wait(parser_t &parser, io_streams_t &streams, const wchar_t **argv) {
     int retval = STATUS_CMD_OK;
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_wait.h b/src/builtin_wait.h
index a9945325b..260977679 100644
--- a/src/builtin_wait.h
+++ b/src/builtin_wait.h
@@ -7,5 +7,5 @@
 class parser_t;
 struct io_streams_t;
 
-maybe_t<int> builtin_wait(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_wait(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
 #endif
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index 52aa2e6c4..2f560f985 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -2768,31 +2768,24 @@ static void test_is_potential_path() {
 }
 
 /// Test the 'test' builtin.
-maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv);
-static bool run_one_test_test(int expected, wcstring_list_t &lst, bool bracket) {
+maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
+static bool run_one_test_test(int expected, const wcstring_list_t &lst, bool bracket) {
     parser_t &parser = parser_t::principal_parser();
-    size_t i, count = lst.size();
-    wchar_t **argv = new wchar_t *[count + 3];
-    argv[0] = (wchar_t *)(bracket ? L"[" : L"test");
-    for (i = 0; i < count; i++) {
-        argv[i + 1] = (wchar_t *)lst.at(i).c_str();
-    }
-    if (bracket) {
-        argv[i + 1] = (wchar_t *)L"]";
-        i++;
-    }
-    argv[i + 1] = NULL;
+    wcstring_list_t argv;
+    argv.push_back(bracket ? L"[" : L"test");
+    argv.insert(argv.end(), lst.begin(), lst.end());
+    if (bracket) argv.push_back(L"]");
+
+    null_terminated_array_t<wchar_t> cargv(argv);
+
     null_output_stream_t null{};
     io_streams_t streams(null, null);
-    maybe_t<int> result = builtin_test(parser, streams, argv);
+    maybe_t<int> result = builtin_test(parser, streams, cargv.get());
 
     if (result != expected) {
         std::wstring got = result ? std::to_wstring(result.value()) : L"nothing";
         err(L"expected builtin_test() to return %d, got %s", expected, got.c_str());
     }
-
-    delete[] argv;
-
     return result == expected;
 }
 
@@ -5551,20 +5544,26 @@ static void test_pcre2_escape() {
     }
 }
 
-maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv);
-static void run_one_string_test(const wchar_t *const *argv, int expected_rc,
+maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, const wchar_t **argv);
+static void run_one_string_test(const wchar_t *const *argv_raw, int expected_rc,
                                 const wchar_t *expected_out) {
+    // Copy to a null terminated array, as builtin_string may wish to rearrange our pointers.
+    wcstring_list_t argv_list(argv_raw, argv_raw + null_terminated_array_length(argv_raw));
+    null_terminated_array_t<wchar_t> argv(argv_list);
+
     parser_t &parser = parser_t::principal_parser();
     string_output_stream_t outs{};
     null_output_stream_t errs{};
     io_streams_t streams(outs, errs);
     streams.stdin_is_directly_redirected = false;  // read from argv instead of stdin
-    maybe_t<int> rc = builtin_string(parser, streams, const_cast<wchar_t **>(argv));
+    maybe_t<int> rc = builtin_string(parser, streams, argv.get());
+
     wcstring args;
-    for (int i = 0; argv[i] != NULL; i++) {
-        args += escape_string(argv[i], ESCAPE_ALL) + L' ';
+    for (const wcstring &arg : argv_list) {
+        args += escape_string(arg, ESCAPE_ALL) + L' ';
     }
     args.resize(args.size() - 1);
+
     if (rc != expected_rc) {
         std::wstring got = rc ? std::to_wstring(rc.value()) : L"nothing";
         err(L"Test failed on line %lu: [%ls]: expected return code %d but got %s", __LINE__,
diff --git a/src/null_terminated_array.cpp b/src/null_terminated_array.cpp
index e374668f2..2e10a9e36 100644
--- a/src/null_terminated_array.cpp
+++ b/src/null_terminated_array.cpp
@@ -1,7 +1,7 @@
 #include "null_terminated_array.h"
 
 template <typename CharT>
-static CharT **make_null_terminated_array_helper(
+static const CharT **make_null_terminated_array_helper(
     const std::vector<std::basic_string<CharT> > &argv) {
     size_t count = argv.size();
 
@@ -48,14 +48,14 @@ static CharT **make_null_terminated_array_helper(
     assert(reinterpret_cast<unsigned char *>(strings) - base ==
            static_cast<std::ptrdiff_t>(pointers_allocation_len + strings_allocation_len));
 
-    return reinterpret_cast<CharT **>(base);
+    return reinterpret_cast<const CharT **>(base);
 }
 
-wchar_t **make_null_terminated_array(const wcstring_list_t &lst) {
+const wchar_t **make_null_terminated_array(const wcstring_list_t &lst) {
     return make_null_terminated_array_helper(lst);
 }
 
-char **make_null_terminated_array(const std::vector<std::string> &lst) {
+const char **make_null_terminated_array(const std::vector<std::string> &lst) {
     return make_null_terminated_array_helper(lst);
 }
 
diff --git a/src/null_terminated_array.h b/src/null_terminated_array.h
index b01ee5edf..b2690ee25 100644
--- a/src/null_terminated_array.h
+++ b/src/null_terminated_array.h
@@ -9,29 +9,32 @@
 
 #include "common.h"
 
-wchar_t **make_null_terminated_array(const wcstring_list_t &lst);
-char **make_null_terminated_array(const std::vector<std::string> &lst);
+const wchar_t **make_null_terminated_array(const wcstring_list_t &lst);
+const char **make_null_terminated_array(const std::vector<std::string> &lst);
+
+/// \return the length of a null terminated array.
+template <typename CharT>
+inline size_t null_terminated_array_length(const CharT *const *arr) {
+    if (!arr) return 0;
+    size_t len = 0;
+    while (arr[len] != nullptr) {
+        len++;
+    }
+    return len;
+}
 
 // Helper class for managing a null-terminated array of null-terminated strings (of some char type).
 template <typename CharT>
 class null_terminated_array_t {
     using string_list_t = std::vector<std::basic_string<CharT>>;
 
-    CharT **array{nullptr};
+    const CharT **array{nullptr};
 
     // No assignment or copying.
     void operator=(null_terminated_array_t rhs) = delete;
     null_terminated_array_t(const null_terminated_array_t &) = delete;
 
-    size_t size() const {
-        size_t len = 0;
-        if (array != nullptr) {
-            while (array[len] != nullptr) {
-                len++;
-            }
-        }
-        return len;
-    }
+    size_t size() const { return nullterm_array_length(array); }
 
     void free(void) {
         ::free(reinterpret_cast<void *>(array));
@@ -74,7 +77,7 @@ class null_terminated_array_t {
     string_list_t to_list() const { return to_list(array); }
 
     const CharT *const *get() const { return array; }
-    CharT **get() { return array; }
+    const CharT **get() { return array; }
 
     void clear() { this->free(); }
 };
diff --git a/src/proc.h b/src/proc.h
index beb072997..e316c360b 100644
--- a/src/proc.h
+++ b/src/proc.h
@@ -233,7 +233,7 @@ class process_t {
     void set_argv(const wcstring_list_t &argv) { argv_array.set(argv); }
 
     /// Returns argv.
-    wchar_t **get_argv() { return argv_array.get(); }
+    const wchar_t **get_argv() { return argv_array.get(); }
     const wchar_t *const *get_argv() const { return argv_array.get(); }
     const null_terminated_array_t<wchar_t> &get_argv_array() const { return argv_array; }
 
diff --git a/src/wgetopt.cpp b/src/wgetopt.cpp
index a73b85a08..2f052b0ff 100644
--- a/src/wgetopt.cpp
+++ b/src/wgetopt.cpp
@@ -65,11 +65,11 @@
 //
 // `first_nonopt' and `last_nonopt' are relocated so that they describe the new indices of the
 // non-options in ARGV after they are moved.
-void wgetopter_t::exchange(wchar_t **argv) {
+void wgetopter_t::exchange(string_array_t argv) {
     int bottom = first_nonopt;
     int middle = last_nonopt;
     int top = woptind;
-    wchar_t *tem;
+    const wchar_t *tem{};
 
     // Exchange the shorter segment with the far end of the longer segment. That puts the shorter
     // segment into the right place. It leaves the longer segment in the right place overall, but it
@@ -139,7 +139,7 @@ void wgetopter_t::_wgetopt_initialize(const wchar_t *optstring) {
 
 // Advance to the next ARGV-element.
 int wgetopter_t::_advance_to_next_argv(  //!OCLINT(high cyclomatic complexity)
-    int argc, wchar_t **argv, const struct woption *longopts) {
+    int argc, string_array_t argv, const struct woption *longopts) {
     if (ordering == PERMUTE) {
         // If we have just processed some options following some non-options, exchange them so
         // that the options come first.
@@ -196,7 +196,7 @@ int wgetopter_t::_advance_to_next_argv(  //!OCLINT(high cyclomatic complexity)
 }
 
 // Check for a matching short opt.
-int wgetopter_t::_handle_short_opt(int argc, wchar_t **argv) {
+int wgetopter_t::_handle_short_opt(int argc, string_array_t argv) {
     // Look at and handle the next short option-character.
     wchar_t c = *nextchar++;
     const wchar_t *temp = std::wcschr(shortopts, c);
@@ -254,8 +254,9 @@ int wgetopter_t::_handle_short_opt(int argc, wchar_t **argv) {
     return c;
 }
 
-void wgetopter_t::_update_long_opt(int argc, wchar_t **argv, const struct woption *pfound,
-                                   wchar_t *nameend, int *longind, int option_index, int *retval) {
+void wgetopter_t::_update_long_opt(int argc, string_array_t argv, const struct woption *pfound,
+                                   const wchar_t *nameend, int *longind, int option_index,
+                                   int *retval) {
     woptind++;
     if (*nameend) {
         // Don't test has_arg with >, because some C compilers don't allow it to be used on
@@ -301,8 +302,8 @@ void wgetopter_t::_update_long_opt(int argc, wchar_t **argv, const struct woptio
 
 // Find a matching long opt.
 const struct woption *wgetopter_t::_find_matching_long_opt(const struct woption *longopts,
-                                                           wchar_t *nameend, int *exact, int *ambig,
-                                                           int *indfound) const {
+                                                           const wchar_t *nameend, int *exact,
+                                                           int *ambig, int *indfound) const {
     const struct woption *pfound = nullptr;
     int option_index = 0;
 
@@ -330,13 +331,13 @@ const struct woption *wgetopter_t::_find_matching_long_opt(const struct woption
 }
 
 // Check for a matching long opt.
-bool wgetopter_t::_handle_long_opt(int argc, wchar_t **argv, const struct woption *longopts,
+bool wgetopter_t::_handle_long_opt(int argc, string_array_t argv, const struct woption *longopts,
                                    int *longind, int long_only, int *retval) {
     int exact = 0;
     int ambig = 0;
     int indfound = 0;
 
-    wchar_t *nameend;
+    const wchar_t *nameend;
     for (nameend = nextchar; *nameend && *nameend != '='; nameend++)
         ;  //!OCLINT(empty body)
 
@@ -419,7 +420,7 @@ bool wgetopter_t::_handle_long_opt(int argc, wchar_t **argv, const struct woptio
 // long-named option has been found by the most recent call.
 //
 // If LONG_ONLY is nonzero, '-' as well as '--' can introduce long-named options.
-int wgetopter_t::_wgetopt_internal(int argc, wchar_t **argv, const wchar_t *optstring,
+int wgetopter_t::_wgetopt_internal(int argc, string_array_t argv, const wchar_t *optstring,
                                    const struct woption *longopts, int *longind, int long_only) {
     if (!initialized) _wgetopt_initialize(optstring);
     woptarg = nullptr;
@@ -452,7 +453,7 @@ int wgetopter_t::_wgetopt_internal(int argc, wchar_t **argv, const wchar_t *opts
     return _handle_short_opt(argc, argv);
 }
 
-int wgetopter_t::wgetopt_long(int argc, wchar_t **argv, const wchar_t *options,
+int wgetopter_t::wgetopt_long(int argc, string_array_t argv, const wchar_t *options,
                               const struct woption *long_options, int *opt_index) {
     return _wgetopt_internal(argc, argv, options, long_options, opt_index, 0);
 }
diff --git a/src/wgetopt.h b/src/wgetopt.h
index 496c27285..2ee594644 100644
--- a/src/wgetopt.h
+++ b/src/wgetopt.h
@@ -43,28 +43,17 @@ Cambridge, MA 02139, USA.  */
 
 #include <stddef.h>
 
+/// Instanced getopt() wrapper.
 class wgetopter_t {
-   private:
-    void exchange(wchar_t **argv);
-    void _wgetopt_initialize(const wchar_t *optstring);
-    int _wgetopt_internal(int argc, wchar_t **argv, const wchar_t *optstring,
-                          const struct woption *longopts, int *longind, int long_only);
-    int _advance_to_next_argv(int argc, wchar_t **argv, const struct woption *longopts);
-    int _handle_short_opt(int argc, wchar_t **argv);
-    bool _handle_long_opt(int argc, wchar_t **argv, const struct woption *longopts, int *longind,
-                          int long_only, int *retval);
-    const struct woption *_find_matching_long_opt(const struct woption *longopts, wchar_t *nameend,
-                                                  int *exact, int *ambig, int *indfound) const;
-    void _update_long_opt(int argc, wchar_t **argv, const struct woption *pfound, wchar_t *nameend,
-                          int *longind, int option_index, int *retval);
-    bool initialized = false;
-    bool missing_arg_return_colon = false;
-
    public:
+    /// Note wgetopter expects an mutable array of const strings. It modifies the order of the
+    /// strings, but not their contents.
+    using string_array_t = const wchar_t **;
+
     // For communication from `getopt' to the caller. When `getopt' finds an option that takes an
     // argument, the argument value is returned here. Also, when `ordering' is RETURN_IN_ORDER, each
     // non-option ARGV-element is returned here.
-    wchar_t *woptarg = nullptr;
+    const wchar_t *woptarg = nullptr;
 
     const wchar_t *shortopts = nullptr;
 
@@ -73,7 +62,7 @@ class wgetopter_t {
     //
     // If this is zero, or a null string, it means resume the scan by advancing to the next
     // ARGV-element.
-    wchar_t *nextchar = nullptr;
+    const wchar_t *nextchar = nullptr;
 
     // Index in ARGV of the next element to be scanned. This is used for communication to and from
     // the caller and for communication between successive calls to `getopt'.
@@ -128,8 +117,25 @@ class wgetopter_t {
 
     wgetopter_t() {}
 
-    int wgetopt_long(int argc, wchar_t **argv, const wchar_t *options,
+    int wgetopt_long(int argc, string_array_t argv, const wchar_t *options,
                      const struct woption *long_options, int *opt_index);
+
+   private:
+    void exchange(string_array_t argv);
+    void _wgetopt_initialize(const wchar_t *optstring);
+    int _wgetopt_internal(int argc, string_array_t argv, const wchar_t *optstring,
+                          const struct woption *longopts, int *longind, int long_only);
+    int _advance_to_next_argv(int argc, string_array_t argv, const struct woption *longopts);
+    int _handle_short_opt(int argc, string_array_t argv);
+    bool _handle_long_opt(int argc, string_array_t argv, const struct woption *longopts,
+                          int *longind, int long_only, int *retval);
+    const struct woption *_find_matching_long_opt(const struct woption *longopts,
+                                                  const wchar_t *nameend, int *exact, int *ambig,
+                                                  int *indfound) const;
+    void _update_long_opt(int argc, string_array_t argv, const struct woption *pfound,
+                          const wchar_t *nameend, int *longind, int option_index, int *retval);
+    bool initialized = false;
+    bool missing_arg_return_colon = false;
 };
 
 /// Describe the long-named options requested by the application. The LONG_OPTIONS argument to