Programming Forums > Application Development > C++

ar1 · Feb 9th, 2005, 1:04 PM

Hi, I wrote the following code which creates a simple shell (like bash). It works fine, can take a command along with arguments and run it or give error if it doesn't exist. However, the strange problem is that it doesn;t execute anything the first time "enter" is hit!! But after that it works perfectly.

I couldn't find the bug, any help would be great. Thanks
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#include <string.h>
#include <errno.h>

#define TRUE 1

void type_prompt();
void *read_command(char *argv[]);
int n = 0;

int main(int argc, char *argv[], char *envp[])
{
char *command;
int status;
argv[0] = NULL;

while (TRUE) /* repeat forever */
{
type_prompt(); /* display prompt on screen */
read_command(argv); /* read input from terminal */

if (fork() != 0) /* fork off child process */
{
waitpid(-1, &status, 0); /* wait for child to exit */
}
else
{
if (execve(argv[0], argv, envp) == -1) /* execute command */
printf("Ouch, can't execute: %s\n", strerror(errno));
}
}
return 0;
}

void type_prompt()
{
printf("[arajgarh]$ ");
}

void *read_command(char *argv[])
{
n = 0;
char temp[256];

gets(temp);
argv[n++] = strtok (temp," ");

while (argv[n-1] != NULL)
argv[n++] = strtok (NULL, " ");
}

Monster · Feb 9th, 2005, 1:14 PM

The first enter is from the read_command function of the parent.

Feb 9th, 2005, 1:04 PM	#1
ar1 Newbie Join Date: Feb 2005 Posts: 1 Rep Power: 0	C program strange error Hi, I wrote the following code which creates a simple shell (like bash). It works fine, can take a command along with arguments and run it or give error if it doesn't exist. However, the strange problem is that it doesn;t execute anything the first time "enter" is hit!! But after that it works perfectly. I couldn't find the bug, any help would be great. Thanks --------------------------------------------------------------------------------------------- (Toggle Plain Text) #include <string.h> #include <errno.h> #define TRUE 1 void type_prompt(); void read_command(char argv[]); int n = 0; int main(int argc, char argv[], char envp[]) { char command; int status; argv[0] = NULL; while (TRUE) / repeat forever / { type_prompt(); / display prompt on screen / read_command(argv); / read input from terminal / if (fork() != 0) / fork off child process / { waitpid(-1, &status, 0); / wait for child to exit / } else { if (execve(argv[0], argv, envp) == -1) / execute command / printf("Ouch, can't execute: %s\n", strerror(errno)); } } return 0; } void type_prompt() { printf("[arajgarh]$ "); } void read_command(char argv[]) { n = 0; char temp[256]; gets(temp); argv[n++] = strtok (temp," "); while (argv[n-1] != NULL) argv[n++] = strtok (NULL, " "); } #include <string.h> #include <errno.h> #define TRUE 1 void type_prompt(); void read_command(char argv[]); int n = 0; int main(int argc, char argv[], char envp[]) { char command; int status; argv[0] = NULL; while (TRUE) /* repeat forever / { type_prompt(); / display prompt on screen / read_command(argv); / read input from terminal / if (fork() != 0) / fork off child process / { waitpid(-1, &status, 0); / wait for child to exit / } else { if (execve(argv[0], argv, envp) == -1) / execute command / printf("Ouch, can't execute: %s\n", strerror(errno)); } } return 0; } void type_prompt() { printf("[arajgarh]$ "); } void read_command(char *argv[]) { n = 0; char temp[256]; gets(temp); argv[n++] = strtok (temp," "); while (argv[n-1] != NULL) argv[n++] = strtok (NULL, " "); }

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Feb 9th, 2005, 1:14 PM	#2
Monster Newbie Join Date: Jan 2005 Posts: 20 Rep Power: 0	The first enter is from the read_command function of the parent.

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Programming Forums > Application Development > C++

C program strange error