c - Why can't my shell start firefox? -

i'm writing small shell exercis learn c. can execute custom commands ls , date when try run firefox doesn't start. why? session

$ ./a.out  minishell>> ls ls a.out      digenv2.c~  digenv.c.orig  minishell.c   readme.md      test digenv     digenv.c    digenv.old.c   minishell.c~  smallshell.c digenv2.c  digenv.c~   license        minishell.c.orig  smallshell.c.orig minishell>> date date tue may 12 09:38:27 cest 2015 minishell>> firefox firefox minishell>> 

my program is

#include <sys/stat.h> #include <stdio.h> #include <unistd.h> #include <string.h> #include <dirent.h> #include <errno.h> #include <stdarg.h> #include <stdlib.h> #include <signal.h> #include <sys/types.h> #include <sys/wait.h>  #define buffer_len 1024 #define buffersize 1024  pid_t foreground = -1;  int mystrcmp(char const *, char const *);  struct command {     char * const *argv; };  void err_syserr(char *fmt, ...) {     int errnum = errno;     va_list args;     va_start(args, fmt);     vfprintf(stderr, fmt, args);     va_end(args);     if (errnum != 0)         fprintf(stderr, "(%d: %s)\n", errnum, strerror(errnum));     exit(exit_failure); }  int startswith(const char *a, const char *b) {    if(strncmp(a, b, strlen(b)) == 0) return 1;    return 0; }   /* helper function spawns processes */ /*static int spawn_proc(int in, int out, struct command *cmd) {     pid_t pid;     if ((pid = fork()) == 0)     {         if (in != 0)         {             if (dup2(in, 0) < 0)                 err_syserr("dup2() failed on stdin %s: ", cmd->argv[0]);                 ;             close(in);         }         if (out != 1)         {             if (dup2(out, 1) < 0)                 err_syserr("dup2() failed on stdout %s: ", cmd->argv[0]);                 close(out);         }         fprintf(stderr, "%d: executing %s\n", (int)getpid(), cmd->argv[0]);         execvp(cmd->argv[0], cmd->argv);           err_syserr("failed execute %s: ", cmd->argv[0]);     }     else if (pid < 0)   {          err_syserr("fork failed: ");      }     return pid; }*/  /* helper function forks pipes */ /*static void fork_pipes(int n, struct command *cmd) {     int i;     int in = 0;     int fd[2];     (i = 0; < n - 1; ++i)     {         pipe(fd);         spawn_proc(in, fd[1], cmd + i);         close(fd[1]);         in = fd[0];     }     if (dup2(in, 0) < 0)    {            err_syserr("dup2() failed on stdin %s: ", cmd[i].argv[0]);     }     fprintf(stderr, "%d: executing %s\n", (int)getpid(), cmd[i].argv[0]);     execvp(cmd[i].argv[0], cmd[i].argv);      err_syserr("failed execute %s: ", cmd[i].argv[0]); }*/   /*remove zoombie processes*/ /*return if background process terminated*/ /* http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html */ void janitor(int status)    {      if(status==sigchld) {   /*child process terminated, stopped, or continued*/          int = 1;          while(a)    {              pid_t pid_my1 = waitpid(-1, &status, wnohang);             /*wnohang = return if no child has exited*/             /*wait*/             /*http://linux.die.net/man/2/waitpid*/              if(0<pid_my1)   {   /*still things clean up*/                   if(pid_my1!=foreground) { /*don't stop me since it's foregound process*/                      /*http://linux.die.net/man/3/wait*/                     if(wifexited(status))   {   /*child process terminated*/                         printf("%d terminated", pid_my1);                     }                 }             }             else {  /*all work done, now*/                 = 0;             }         }     } }        int main() {     char line[buffer_len];       char* argv[100];             char* path= "/bin/";         char progpath[20];           int argc;                    size_t length;     char *token;     int i=0;     int pid;     char *tokenstr;     char *search = " ";      int issignal = 0;     int isbackground = 0;      #ifdef sigdet         #if sigdet == 1             issignal = 1;       /*termination detected signals*/         #endif     #endif       while(1) {     = 0;     int built_in_command = 0;         printf("minishell>> ");                              if(!fgets(line, buffer_len, stdin)) {              break;                                         }         length = strlen(line);         if (line[length - 1] == '\n') {             line[length - 1] = '\0';         }         if(strcmp(line, "exit")==0) {                        break;         }          if(startswith(line, "cd")) {                         built_in_command=1;              printf("change directory\n");             tokenstr = strtok(line, search);             tokenstr = strtok(null, search);             chdir(tokenstr);         /*todo maybe have check whether argument exist, if not go home directory*/          }          token = strtok(line," ");          while(token!=null) {             argv[i]=token;             token = strtok(null," ");             i++;         }          if(startswith(line, "checkenv")) {              built_in_command=1;             if (0==i)   {                  char *printenv[] = { "printenv", 0};                 char *sort[] = { "sort", 0 };                 char *less[] = { "less", 0 };                 struct command cmd[] = { {printenv}, {sort}, {less} };                  fork();             }             else    {                  char *tmp;                 int len = 1;                 (i = 1; < argc; i++)                 {                     len += strlen(argv[i]) + 2;                 }                 tmp = (char *) malloc(len);                 tmp[0] = '\0';                 int pos = 0;                 (i = 1; < argc; i++)                 {                     pos += sprintf(tmp + pos, "%s%s", (i == 1 ? "" : "|"), argv[i]);                 }                 char *printenv[] = { "printenv", 0};                 char *grep[] = { "grep", "-e", tmp, null};                 char *sort[] = { "sort", 0 };                 char *less[] = { "less", 0 };                 struct command cmd[] = { {printenv}, {grep}, {sort}, {less} };                 fork();                 free(tmp);             }         }            if(0==built_in_command) {   /*not built in command, let execute it*/              argv[i]=null;                                   argc=i;                                        for(i=0; i<argc; i++) {                 printf("%s\n", argv[i]);                 }             strcpy(progpath, path);                        strcat(progpath, argv[0]);                          for(i=0; i<strlen(progpath); i++) {                    if(progpath[i]=='\n') {                     progpath[i]='\0';                 }             }                isbackground = 0;              sigset_t my_sig;              pid_t pid_temp;               int lastelem = (sizeof(line)/sizeof(line[0]))-1;    /*last input argument index*/             /*todo check if background process*/                /*todo store time forground process started*/              int fd[2];             if (isbackground == 1)  {   //if backgroundprocess                  pipe(fd);  /*(two new file descriptors)*/                  /*fixme pid_temp = fork_pipes(2, .....);*/                 pid_temp = fork();             }              else if (isbackground == 0) {   //if foreground process                  int issignal = 0;   /*fixme*/                 if (1 == issignal)  {   /*if using signaldetection*/                      sigemptyset(&my_sig); /*empty , initialising signal set*/                     sigaddset(&my_sig, sigchld);    /*adds signal signal set (my_sig)*/                     /*http://pubs.opengroup.org/onlinepubs/7908799/xsh/sigprocmask.html*/                     sigprocmask(sig_block, &my_sig, null);                 }                  /*fixme pid_temp = fork_pipes(2, .....);*/                  pid_temp = fork();                 foreground = pid_temp;  /*set pid foreground process*/              }               if (0<pid_temp) {                 /*parent process*/             }              else if (0>pid_temp)    {                 /*error*/             }              else    {                 /*child process*/                  if (1 == isbackground)  {   //backgroundprocess                      dup2(fd[stdin_fileno], stdin_fileno);                      close(fd[0]);                     close(fd[1]);                  }                  execvp(progpath,argv); /*todo execute command here, working*/             }              if (0 == isbackground)  {   //foregroundprocess                    /*write here, emil*/                 int status = 0;                 waitpid(pid_temp, &status, 0);                  /*foregroundprocess terminated*/                 /*todo how long time total execution time*/                    int issignal = 0;   /*fixme*/                 if (1 == issignal)  {   /*if using signaldetection*/                      int = sigprocmask(sig_unblock, &my_sig, null);                     /*http://man7.org/linux/man-pages/man2/sigprocmask.2.html*/                      if (0 == a) {                         /*sigprocmask successfull*/                     }                     else    {                         /*sigprocmask not successfull, return=-1*/                     }                     janitor(sigchld);                 }             }              else if (1==isbackground)   {                  close(fd[0]);                 close(fd[1]);             }         }            /* pid= fork();                        if(pid==0) {                           execvp(progpath,argv);             fprintf(stderr, "child process not execvp\n");          } else {                               wait(null);             printf("child exited\n");         }*/      } return (0); }  int mystrcmp(char const *p, char const *q) {     int = 0;     for(i = 0; q[i]; i++)     {         if(p[i] != q[i])             return -1;     }     return 0; }  int cd(char *pth) {     char path[buffersize];     char cwd[buffersize];     char * return_value;     int other_return;     strcpy(path,pth);      if(pth[0] != '/')     {           return_value = getcwd(cwd,sizeof(cwd));         strcat(cwd,"/");         strcat(cwd,path);         other_return = chdir(cwd);     } else {          other_return = chdir(pth);     }     printf("spawned foreground process: %d\n", getpid());     return 0; } 

the issue path. assume command in /bin/ whereas firefox in /usr/bin/. child going exec /bin/firefox , fail. checking return code of execvp have helped finding this. on success, execvp family functions don't return. if do, know why.