Question

Writing your own shell in Linux with execvp

Only code void cmdToArray()

Program should be able to execute ls -l.

#include <stdio.h>
#include <string,h>// strcmp
#include <stdlib.h>// exit
#include <unistd.h>// fork, exec
#include <sys/wait.h>// wait

#define MAXARGS 20
#define ARGLEN 256

void execute(char *cmd, char *arglist[]);
void cmdToArray(char *cmd, char *arglist);

int main(void)
{
int pid;
char *arglist[MAXARGS+1]; // array of pointers
char cmd[ARGLEN]; // read stuff here

while (1)
{
printf("cmd> ");
fgets(cmd, ARGLEN, stdin);

// remove newline from cmd
cmd[strlen(cmd) - 1] = '\0';

// exit if user types exit
if (strcmp(cmd, "exit") == 0)
{
exit(0);
}
else if (*cmd != '\0')
{
// TODO: break cmd into individual strings as elements of arglist
cmdToArray(cmd, arglist);
execute(arglist);
}
}

return 0;
}

void cmdToArray(char *cmd, char *arglist[]) //code here
{
// cmd = "*cp file1.txt file2.txt"
// char cmd[25] = ('c', 'p', ' ', 'f', ')
// arglist[0] = cmd;
// arglist[1] = &cmd[3];
// arglist[2] = &cmd[9];
// arglist[3] = "NULL";
// arglist = (**char)malloc(sizeof(char*) * cmd);
// arglist[0] = (char *)malloc(sizeof(char) *MAXARGS * string);
// int length = strlen(cmd);
/* for (int i = 0; i < length; ++i)
{
if (cmd[i] != ' ')
{
arglist[argc] = &cmd[i];
++argc;
}
else if(cmd[i] == ' ')
{
cmd[i] = '\0';
}
} */

}

void execute(char *arglist[])
{
int pid, exitstatus;

pid = fork(); // make new process
if (pid == -1)
{
perror("fork failed");
exit(1);
}
else if (pid == 0)
{
execvp(arglist[0], arglist);
// exec cannot return
fprintf(stderr, "Cannot execute %s\n", arglist[0]);
exit(1); // exec failed
}
else
{
int got_pid = wait(&exitstatus);
if (got_pid == pid)
{
printf("The child we were waiting for died\n");

if (WIFEXITED(exitstatus))
{
printf("child process %d exited with value %d\n", pid, WEXITSTATUS(exitstatus));
}
}
else if (got_pid == -1)
{
perror("wait failed");
}
}
}

Answer 1

#include <stdio.h>
#include <string.h>// strcmp
#include <stdlib.h>// exit
#include <unistd.h>// fork, exec
#include <sys/wait.h>// wait

#define MAXARGS 20
#define ARGLEN 256

void execute(char *cmd, char *arglist[]);
void cmdToArray(char *cmd, char *arglist);

int main(void)
{
int pid;
char *arglist[MAXARGS+1]; // array of pointers
char cmd[ARGLEN]; // read stuff here

while (1)
{
printf("cmd> ");
fgets(cmd, ARGLEN, stdin);

// remove newline from cmd
cmd[strlen(cmd) - 1] = '\0';

// exit if user types exit
if (strcmp(cmd, "exit") == 0)
{
exit(0);
}
else if (*cmd != '\0')
{
// TODO: break cmd into individual strings as elements of arglist
cmdToArray(cmd, arglist);
execute(arglist);
}
}

return 0;
}

void cmdToArray(char *cmd, char *arglist[]) //code here
{
// cmd = "*cp file1.txt file2.txt"
// char cmd[25] = ('c', 'p', ' ', 'f', ')
// arglist[0] = cmd;
// arglist[1] = &cmd[3];
// arglist[2] = &cmd[9];
// arglist[3] = "NULL";
// arglist = (**char)malloc(sizeof(char*) * cmd);
// arglist[0] = (char *)malloc(sizeof(char) *MAXARGS * string);
// int length = strlen(cmd);
/* for (int i = 0; i < length; ++i)
{
if (cmd[i] != ' ')
{
arglist[argc] = &cmd[i];
++argc;
}
else if(cmd[i] == ' ')
{
cmd[i] = '\0';
}
} */

}

void execute(char *arglist[])
{
int pid, exitstatus;

pid = fork(); // make new process
if (pid == -1)
{
perror("fork failed");
exit(1);
}
else if (pid == 0)
{
execvp(arglist[0], arglist);
// exec cannot return
fprintf(stderr, "Cannot execute %s\n", arglist[0]);
exit(1); // exec failed
}
else
{
int got_pid = wait(&exitstatus);
if (got_pid == pid)
{
printf("The child we were waiting for died\n");

if (WIFEXITED(exitstatus))
{
printf("child process %d exited with value %d\n", pid, WEXITSTATUS(exitstatus));
}
}
else if (got_pid == -1)
{
perror("wait failed");
}
}
}