Provide subshell command ! in the terminal

Needs to have allow_subshells = yes; in ~/.avrduderc. Then subshell
commands can be executed, eg,

$ avrdude -t

avrdude> !ls
myapplication.hex    myapplication.eep

avrdude> !avrdude -pm328p/St | grep efuse.initval
.ptmm   ATmega328P      efuse   initval 0xff

src/avrdude.conf.in

@@ -421,6 +421,7 @@ default_serial     = "@DEFAULT_SER_PORT@";
 default_spi        = "@DEFAULT_SPI_PORT@";
 # default_bitclock = 2.5;
 default_linuxgpio  = "@DEFAULT_LINUXGPIO_PORT@";
+allow_subshells    = no;
 
 @HAVE_PARPORT_BEGIN@
 

src/config.c

@@ -41,6 +41,7 @@ const char *default_serial;
 const char *default_spi;
 double default_bitclock;
 char const *default_linuxgpio;
+int allow_subshells;
 
 LISTID       string_list;
 LISTID       number_list;

src/config_gram.y

@@ -73,6 +73,7 @@ static int pin_name;
 %token K_PAGE_SIZE
 
 %token K_ALIAS
+%token K_ALLOW_SUBSHELLS
 %token K_BUFF
 %token K_CONNTYPE
 %token K_DEDICATED
@@ -233,6 +234,11 @@ def :
     free_token($3);
   } |
 
+  K_ALLOW_SUBSHELLS TKN_EQUAL numexpr TKN_SEMI {
+    allow_subshells = $3->value.number;
+    free_token($3);
+  } |
+
   K_DEFAULT_LINUXGPIO TKN_EQUAL TKN_STRING TKN_SEMI {
     default_linuxgpio = cache_string($3->value.string);
     free_token($3);

src/developer_opts.c

@@ -905,6 +905,7 @@ void dev_output_pgm_part(int dev_opt_c, const char *programmer, int dev_opt_p, c
     dev_info("default_spi        = %s;\n", p = cfg_escape(default_spi)); free(p);
     dev_info("default_bitclock   = %7.5f;\n", default_bitclock);
     dev_info("default_linuxgpio  = %s;\n", p = cfg_escape(default_linuxgpio)); free(p);
+    dev_info("allow_subshells    = %s;\n", allow_subshells? "yes": "no");
 
     dev_info("\n#\n# PROGRAMMER DEFINITIONS\n#\n\n");
   }

src/doc/avrdude.texi

@@ -2701,6 +2701,15 @@ option.
 Assign the default bitclock value.  Can be overridden using the @option{-B}
 option.
 
+@item allow_subshells = @var{no};
+Whether or not AVRDUDE's interactive terminal is allowed to use subshell
+@code{!} commands. This defaults to no for security reasons, eg, in the
+rare case @code{avrdude -t} is set up with attached hardware to provide a
+web service, remote ssh or a login on a PC instead of a shell, say, for
+demo or training purposes. In almost all other cases this can be
+overridden in the personal @code{avrddude.rc} or @code{.avrduderc}
+configuration file with @var{yes}.
+
 @end table
 
 

src/lexer.l

@@ -179,6 +179,7 @@ INF  [Ii][Nn][Ff]([Ii][Nn][Ii][Tt][Yy])?
 }
 
 alias            { yylval=NULL; return K_ALIAS; }
+allow_subshells  { yylval=NULL; return K_ALLOW_SUBSHELLS; }
 allowfullpagebitstream { yylval=NULL; ccap(); return K_ALLOWFULLPAGEBITSTREAM; }
 buff             { yylval=NULL; ccap(); return K_BUFF; }
 chip_erase       { yylval=new_token(K_CHIP_ERASE); ccap(); return K_CHIP_ERASE; }

src/libavrdude.h

@@ -1136,14 +1136,15 @@ void walk_programmer_types(/*LISTID programmer_types,*/ walk_programmer_types_cb
 
 /* formerly config.h */
 
-extern LISTID       part_list;
-extern LISTID       programmers;
+extern LISTID      part_list;
+extern LISTID      programmers;
 extern const char *default_programmer;
 extern const char *default_parallel;
 extern const char *default_serial;
 extern const char *default_spi;
-extern double       default_bitclock;
-extern char const * default_linuxgpio;
+extern double      default_bitclock;
+extern char const *default_linuxgpio;
+extern int         allow_subshells;
 
 /* This name is fixed, it's only here for symmetry with
  * default_parallel and default_serial. */

src/main.c

@@ -573,6 +573,7 @@ int main(int argc, char * argv [])
   default_spi        = "";
   default_bitclock   = 0.0;
   default_linuxgpio  = "";
+  allow_subshells    = 0;
 
   init_config();
 

src/term.c

@@ -1675,7 +1675,7 @@ static int cmd_help(const PROGRAMMER *pgm, const AVRPART *p, int argc, char *arg
     term_out(cmd[i].desc, cmd[i].name);
     term_out("\n");
   }
-  term_out("\n"
+  term_out("  !<scmd> : run the command <scmd> in a subshell, eg, !ls\n\n"
     "For more details about a terminal command cmd type cmd -?\n\n"
     "Note that not all programmer derivatives support all commands. Flash and\n"
     "EEPROM type memories are normally read and written using a cache via paged\n"
@@ -1896,6 +1896,21 @@ static int process_line(char *q, const PROGRAMMER *pgm, const AVRPART *p) {
   if (!*q || (*q == '#'))
     return 0;
 
+  if(*q == '!') {
+    if(allow_subshells) {
+      while(*++q && isspace((unsigned char) *q))
+        continue;
+      errno = 0;
+      int shret = *q? system(q): 0;
+      if(errno)
+        pmsg_warning("system() call returned %d: %s\n", shret, strerror(errno));
+    } else {
+      pmsg_warning("subshell commands are by default not allowed in the terminal\n");
+      imsg_warning("allow_subshells = yes; in avrdude.rc or ~/.avrduderc changes this\n");
+    }
+    return 0;
+  }
+
   // Tokenize command line
   do {
     argc = 0; argv = NULL;