I have to develop a simple shell in C using system calls fork()/execvp(). So far my code takes in a command, splits it up using strtok into an array argv and then I call fork to create a child and execute the command. Im working on this in ubuntu where most of the commands are in the /bin/ directory, so I append the program name (for example /bin/ls) and use that for the first arg of execvp and then I give it the argv array. My program works if I type in the command "ls", but when trying other commands or even "ls -l" I'm getting an "ls: invalid option." Im not sure what I'm doing wrong here.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFER_LEN 1024
int main(){
char line[BUFFER_LEN]; //get command line
char* argv[100]; //user command
char* path= "/bin/"; //set path at bin
char progpath[20]; //full file path
int argc; //arg count
while(1){
printf("My shell>> "); //print shell prompt
if(!fgets(line, BUFFER_LEN, stdin)){ //get command and put it in line
break; //if user hits CTRL+D break
}
if(strcmp(line, "exit\n")==0){ //check if command is exit
break;
}
char *token; //split command into separate strings
token = strtok(line," ");
int i=0;
while(token!=NULL){
argv[i]=token;
token = strtok(NULL," ");
i++;
}
argv[i]=NULL; //set last value to NULL for execvp
argc=i; //get arg count
for(i=0; i<argc; i++){
printf("%s\n", argv[i]); //print command/args
}
strcpy(progpath, path); //copy /bin/ to file path
strcat(progpath, argv[0]); //add program to path
for(i=0; i<strlen(progpath); i++){ //delete newline
if(progpath[i]=='\n'){
progpath[i]='\0';
}
}
int pid= fork(); //fork child
if(pid==0){ //Child
execvp(progpath,argv);
fprintf(stderr, "Child process could not do execvp\n");
}else{ //Parent
wait(NULL);
printf("Child exited\n");
}
}
}
Like all of the exec functions, execvp replaces the calling process image with a new process image. This has the effect of running a new program with the process ID of the calling process. Note that a new process is not started; the new process image simply overlays the original process image.
FILE *fp; char *command; /* command contains the command string (a character array) */ /* If you want to read output from command */ fp = popen (command,"r"); /* read output from command */ fscanf(fp,....); /* or other STDIO input functions */ fclose(fp); /* If you want to send input to command */ fp = popen (command," ...
The invalid option is because fgets()
keeps the '\n'
when you press enter, try this
if(!fgets(line, BUFFER_LEN, stdin))
break;
size_t length = strlen(line);
if (line[length - 1] == '\n')
line[length - 1] = '\0';
when you are trying to call ls -l
you are passing "-l\n"
as the option, hence the message.
You will have to change
strcmp(line, "exit\n")
to
strcmp(line, "exit")
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