I'm trying to write a very very simple unix shell in C, and I have the basics of what I need working, except support for a history command. I have a global 2D char array that holds the history of all entered commands. Commands are added before the fork() system call, and I was originally printing out the value of the history global array after strings were added, and they were printing out correctly, so I'm not sure why it doesn't print out when the command "history" is used at the shell.
Thank to anyone who takes a look.
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include "myhistory.h"
int BUFFER_SIZE = 1024;
char history[100][80];
int command_index = 0;
int main(int argc, char *argv[]){
int status = 0;
int num_args;
pid_t pid;
while(1){
char *buffer_input, *full_input;
char command[BUFFER_SIZE];
char *args[BUFFER_SIZE];
printf("myshell> ");
buffer_input = fgets(command, 1024, stdin);
full_input = malloc(strlen(buffer_input)+1);
strcpy(full_input, buffer_input);
if (command_index >= 100) {
command_index = 0;
}
strncpy(history[command_index], full_input, strlen(full_input) + 1);
command_index += 1;
parse_input(command, args, BUFFER_SIZE, &num_args);
//check exit and special command conditions
if (num_args==0)
continue;
if (!strcmp(command, "quit" )){
exit(0);
}
if(!strcmp(command, "history")){
int i;
fprintf(stderr,"%d\n",(int)pid);
for(i = 0; i < command_index; i++){
fprintf(stdout, "%d: %s\n",i+1,history[command_index]);
}
continue;
}
errno = 0;
pid = fork();
if(errno != 0){
perror("Error in fork()");
}
if (pid) {
pid = wait(&status);
} else {
if( execvp(args[0], args)) {
perror("executing command failed");
exit(1);
}
}
}
return 0;
}
void parse_input(char *input, char** args,
int args_size, int *nargs){
char *buffer[BUFFER_SIZE];
buffer[0] = input;
int i = 0;
while((buffer[i] = strtok(buffer[i], " \n\t")) != NULL){
i++;
}
for(i = 0; buffer[i] != NULL; i++){
args[i] = buffer[i];
}
*nargs = i;
args[i] = NULL;
}
Change:
fprintf(stdout, "%d: %s\n",i+1,history[command_index]);
to:
fprintf(stdout, "%d: %s\n",i+1,history[i]);
Related
I am working on a shell command program in C, I have it working but the output is not formatted correctly. I am unable to see where the problem lies. I have read through the code several times and I am not seeing the issue. I have tried placing \n in various places but that typicality results in worse formatting.
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <wait.h>
#include <stdlib.h>
#include <termios.h>
#include <fcntl.h>
#define MAX_LINE 80 /*Maximum length of a command*/
#define MAX_HST 10
int main(void){
char getInput[MAX_LINE];
char *args[MAX_LINE/2+1]; /*command line arguments*/
int should_run = 1; /*Flag to determine when to exit the program*/
int numCommand = 0;
int cmdHst = 0;
char *cmdHistory[MAX_HST];
char *myCmd;
while (should_run = 1){
printf("osh> ");
fflush(stdout);
fgets(getInput, MAX_LINE, stdin);//read input command
if(strcmp(getInput, "!!\n") == 0){//Command history
if(cmdHst == 0){
printf("No previous commands.\n");
}
for (int i= 0; i<cmdHst; i++){//display all commands in history
strncpy(getInput, cmdHistory[i], MAX_LINE);
printf("%s\n", getInput);
}
}
if (cmdHst < MAX_HST){
cmdHistory[cmdHst] = strdup(getInput);
cmdHst++;
}
else{//shift commands in history to fill gaps
for(int i = 1; i < cmdHst; i++){
free(cmdHistory[i-1]);
cmdHistory[i-1]= strdup(cmdHistory[i]);
}
free(cmdHistory[cmdHst-1]);
cmdHistory[MAX_HST-1] = strdup(getInput);
}
//parsing commands into tokens
numCommand = 0;
args[numCommand] = strtok(getInput, " \n");
while(args[numCommand] != NULL){
numCommand++;
args[numCommand] = strtok(NULL, " \n");
}
args[numCommand]=NULL;
if(strcmp(args[0], "exit")==0){//Check for exit command
should_run =0;
break;
}
pid_t pid = fork();//Create child process
if(pid < 0){
fprintf(stderr, "Fork Failed\n");
return 1;
}
else if(pid == 0){
if(execvp(args[0], args)==-1){
fprintf(stderr, "Command Not Found.\n");
exit(1);
}
else{
if(args[numCommand-1][0] != '&'){
wait(NULL);
}
}
}
}
for(int i = 0; i < cmdHst; i++){//free histrry array
free(cmdHistory[i]);
}
return 0;
}
I have read over the code a few times and tried in putting fprintf("\n");s in various places.
I forgot the parent wait(NULL) command. That fixed it.
So I'm trying to create a custom shell for my school project. My method was to create child process, and have that process execute the command using the execvp() function that my professor briefly mentioned in class that we are meant to use. Here's my code, as always, any help is appreciated.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#define MAX_LINE 80
int main(int argc, char *argv[])
{
char *input = (char*)malloc(MAX_LINE*sizeof(char));
int should_run = 1;
while(should_run){
printf("osh>");
fflush(stdout);
pid_t pid;
pid = fork();
if(pid < 0){
printf("error with creating chiled process");
return 0;
}
if(pid == 0){
fgets(input, MAX_LINE, stdin);
char *token = strtok(input," ");
if(execvp(token[0], token) < 0){
printf("Error in execution.");
return(0);
}
//should_run = 0;
}
waitpid(pid, 1, 0);
}
return 0;
}
The prototype of execvp is
int execvp(const char *file, char *const argv[]);
It expects a pointer to char as the first argument, and a NULL-terminated
pointer to an array of char*. You are passing completely wrong arguments.
You are passing a single char as first argument and a char* as the second.
Use execlp instead:
int execlp(const char *file, const char *arg, ...
/* (char *) NULL */);
So
char *token = strtok(input," \n");
if(token == NULL)
{
fprintf(stderr, "only delimiters in line\n");
exit(1);
}
if(execlp(token, token, NULL) < 0){
fprintf(stderr, "Error in execution: %s\n", strerror(errno));
exit(1);
}
Also the convention in UNIX is to print error messages to stderr and a process with an error should
have an exit status other than 0.
As Pablo's states, you are passing the wrong arguments to execvp().
You can consider coding by yourself a function (char **strsplit(char *str, char delim)) which takes a string and split it into smaller pieces, returning an array of strings.
Also don't ignore compiler's warnings, they tell you a lot of things, and I suggest you to compile with gcc -Wall -Wextra -Werror to get almost any possible error in your program.
I tell you this because waitpid() takes as second argument a pointer to integer, to get an update of the status of the forked program. With this status you how the program exited (normally, segf, bus error...), you can use it to print an error if something went wrong.
You can consider using execv() instead (I know I'm going off topic, but you can learn useful things doing this), and find by yourself the correct executable(s).
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#define MAX_LINE 255
char **strsplit(char *str, char delim);
char *strjoin(char const *s1, char const *s2);
int isexec(char *path)
{
struct stat buf;
lstat(path, &buf);
if (S_ISREG(buf.st_mode) && (S_IXUSR & buf.st_mode))
return (1);
return (0);
}
static char *find_exec_readdir(char *paths, char *cmd)
{
DIR *dir;
struct dirent *dirent;
char *exec;
exec = NULL;
if ((dir = opendir(paths)) != NULL)
{
while ((dirent = readdir(dir)) != NULL)
{
if (!strcmp(dirent->d_name, cmd))
{
exec = strdup(dirent->d_name);
break ;
}
}
if (closedir(dir))
dprintf(2, "Failed closing dir.\n");
}
return (exec);
}
char *find_exec(char *cmd, char **paths)
{
char *exec;
char *path;
char *tmp;
int i;
i = -1;
exec = NULL;
path = NULL;
if ((cmd[0] == '.' || cmd[0] == '/'))
{
if (isexec(cmd))
return (strdup(cmd));
return (NULL);
}
while (paths[++i])
if ((exec = find_exec_readdir(paths[i], cmd)) != NULL)
{
tmp = strjoin(paths[i], "/");
path = strjoin(tmp, exec);
free(tmp);
free(exec);
break ;
}
return (path);
}
int handle_return_status(int status)
{
int sig;
int i;
if (!WIFEXITED(status) && WIFSIGNALED(status))
{
sig = WTERMSIG(status);
i = -1;
while (++i <= 13)
{
if (print_signal_error(sig))
{
return (-1);
}
}
dprintf(2, "Process terminated with unknown signal: %d\n", sig, NULL);
return (-1);
}
return (0);
}
int main(int argc, char *argv[])
{
char *input = NULL;
char **command = NULL;
int should_run = 1;
int status = 0;
(void)argc;
(void)argv;
if ((input = (char*)malloc(MAX_LINE*sizeof(char))) == NULL)
return (dprintf(2, "Failed to malloc, abort.\n"));
while(should_run){
printf("osh> ");
fflush(stdout);
pid_t pid;
pid = fork();
if(pid < 0)
return (dprintf(2, "error with creating chiled process\n"));
if(pid == 0){
fgets(input, MAX_LINE, stdin);
command = strsplit(input, ' ');
command[0] = find_exec(command[0], strsplit(getenv("PATH"), ':'));
if(execv(command[0], &command[1]) < 0)
return (dprintf(2, "Error in execution.\n"));
//should_run = 0;
}
waitpid(pid, &status, 0);
handle_ret_status(status);
}
return 0;
}
I'm creating my own Shell and I successfully got processes to run in the background by using my is_background function to find a &. It was working fine until i tried to implement redirection of standard output. The chk_if_output function is a part of this as well as the if statement if(out[0] == 1) in the process function. Somehow implementing redirection screwed up the way I implemented background process. If I comment out the redirection code it works again. I get a segmentation fault every time I try to run a background process with the redirection code in the program and I can't for the life of me figure out why. I haven't changed any of the background process code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#define MAX_LINE 80 /* The maximum length command */
int is_background(char *args[], int size){
int background = 0;
if (strcmp(args[size-1 ], "&") == 0){
background = 1;
args[size-1] = NULL;
}
return background;
}
int * chk_if_output(char *args[], int size){
int * out = malloc(2);
out[0] = 0; out[1] = 0;
for (int i = 0; i < size; i++){
if (strcmp(args[i],">") == 0){
out[0] = 1;
out[1] = i;
break;
}
}
return out;
}
void process(char *command, char *params[], int size){
pid_t pid;
int background = is_background(params, size);
int *out = chk_if_output(params, size);
int fd;
int fd2;
pid = fork();
if (pid < 0) {
fprintf(stderr, "Fork Failed\n");
}else if (pid == 0) {
if(out[0] == 1){
for (int i = out[1]; i < size; i++){
params[i] = params[i+1];
}
fd = open(params[out[1]-1],O_RDONLY,0);
dup2(fd,STDIN_FILENO);
close(fd);
fd2 = creat(params[out[1]],0644);
dup2(fd2,STDOUT_FILENO);
close(fd2);
out[0] = 0;
out[1] = 0;
}
execvp(command, params);
}else {
if(background == 1){
waitpid(pid, NULL, 0);
}
background = 0;
}
}
int main(void) {
char *args[MAX_LINE/2 + 1]; /* command line arguments */
int should_run = 1; /* flag to determine when to exit program */
while (should_run) {
char *line;
char *endline;
printf("Leyden_osh>");
fgets(line, MAX_LINE*sizeof line, stdin);
if((endline = strchr(line, '\n')) != NULL){
*endline = '\0';
}
if (strcmp((const char *)line,"exit") == 0){
should_run = 0;
}
int i = 0;
args[i] = strtok(line, " ");
do{
args[++i] = strtok(NULL, " ");
}while(args[i] != NULL);
process(args[0], args, i);
fflush(stdout);
return 0;
}
In the chk_if_output() function, the last element of the array in the loop was NULL.
Fixed it by looping to size -1.
I am trying to make a tiny shell. My problem is that when I call execvp() - I get errors.
For example, when I type in ls -l it returns ls: invalid option -- '
Can someone, please, help me understand why I am getting this error? For my code, the function command split gets the user input, and splits them up into separate commands. Separate commands are seperated by ; character.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#define MAX_CHARACTERS 512
#define HISTORY_SIZE 10
int commandSplit(char *c, char *a[], int t[]) {
int count = 0;
int total = 0;
char *temp[MAX_CHARACTERS];
char *readCommands = strtok(c, ";");
while(readCommands != NULL) {
printf("Reading full command: %s\n", readCommands);
temp[count] = readCommands;
count++;
readCommands = strtok(NULL, ";");
}
printf("Done reading full commands\n");
for(int i = 0; i < count; i++) {
char *read = strtok(temp[i], " ");
int track = 0;
while(read != NULL) {
printf("Reading individual command: %s\n", read);
a[total] = read;
track++;
total++;
read = strtok(NULL, " ");
}
t[i] = track;
}
return count;
}
int main() {
int exitProgram = 0;
char *args[MAX_CHARACTERS];
while(!exitProgram) {
char *commands = (char *)(malloc(MAX_CHARACTERS*sizeof(char)));
int tracker[MAX_CHARACTERS];
int numOfCommands = 0;
printf("tinyshell> ");
fgets(commands, MAX_CHARACTERS, stdin);
if(strlen(commands) == 0) continue;
numOfCommands = commandSplit(commands, args, tracker);
printf("There are %i commands!\n", numOfCommands);
if(strcmp(args[0], "exit") == 0) {
printf("Exiting\n");
exitProgram = 1;
continue;
}
int l = 0;
for(int i = 0; i < numOfCommands; i++) {
int status;
char *holder[tracker[i]+1];
for(int j = 0; j < tracker[i]; j++) {
holder[j] = args[l];
printf("Assiging holder:%s\n", holder[j]);
l++;
}
holder[tracker[i]] = NULL;
printf("What is holder? \n");
for(int o = 0; o < tracker[i]; o++) printf("%s", holder[o]);
pid_t p = fork();
pid_t waiting;
if(p == 0) {
printf("I am in child process\n");
execvp(holder[0], holder);
fprintf(stderr, "Child process could not execvp!\n");
exit(1);
}
else {
if(p < 0) {
fprintf(stderr, "Fork FAILED!\n");
}
else {
waiting = wait(&status);
printf("Child %d, status %d\n", waiting, status);
}
}
for(int i = 0; i < numOfCommands; i++) {
args[i] = NULL;
}
}
}
return 0;
}
Your problem is that fgets() also reads the newline character. As a result, the last argument of execvp() arguments array contains a newline, causing ls complain about an unrecognized argument: what you acctually pass to ls is -l\n; what you need to pass is just -l without the newline.
Try adding this code after the fgets call to trim the input buffer:
int len;
len = strlen(commands);
if (len > 0 && commands[len-1] == '\n') {
commands[len-1] = '\0';
}
I am experimenting with writing a simple shell to support all the usual functions.
So far, despite my haphazard approach to it, I have been met with success - I have been able to fork() new processes with parameters but other certain methods don't seem to run.
When I run my shell, functions like pwd, ls, help work whilst other functions such as cd, mkdir don't - why is this & what research/investigation can I do in order to begin to address this?
I've included my code so far (although I'm not sure if it will actually help).
Thanks very much
EDIT: My output, when my shell is running in cygwin, if I type "cd /cygdrive/c" the output is "Command not found"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
const int MAX_ARGS = 9;
size_t nBytes = 64; //Data type representing size of objects (unsigned)
int bytesRead = -1;
char *cmd = NULL;
char prompt[] = "DaSh-> ";
int argc;
char **argv;
int pid;
int childpid;
int status;
void process();
int readcmd();
int main() {
setvbuf(stdout, NULL, _IONBF, 0);
setvbuf(stderr, NULL, _IONBF, 0);
while (1) {
bytesRead = -1;
printf(prompt);
while (bytesRead == -1) {
bytesRead = readcmd();
}
process(cmd); //process the single line input into arguments
if (strcmp(argv[0], "exit") == 0) { //If user types exit
exit(0);
}
childpid = fork();
if (childpid == 0) { //This is run by the child
execvp(argv[0], argv);
printf("Command not recognised\n");
exit(1);
}
else if (childpid > 0 ) {
waitpid(-1, &status, 0);
}
}
return 0;
}
int nrows = 10;
int ncolumns = 2;
void process(char argStr[]) {
argv = malloc(MAX_ARGS * sizeof(char *)); //Array of pointers to the char first letter of each argument
char delims[] = " \n"; //Delimit about space
int i = 0;
argv[i] = strtok(argStr, delims);
while (argv[i] != NULL) {
argv[++i] = strtok( NULL, delims);
}
argc = i;
}
int readcmd() {
return getline(&cmd, &nBytes, stdin);
}