1.chgrp实现

#include <grp.h>
#include <unistd.h>

void chgrp(char * groupname,char * filename)
{
    struct group * groupinfo = NULL;
    if((groupinfo = getgrnam(groupname)) == NULL)
    {
        printf("groupname does not exist\n");
        return;
    }

    if(access(filename,F_OK) != 0)
    {
        printf("file %s does not exist\n",filename);
        return;
    }

    int gid = groupinfo->gr_gid;
    chown(filename,-1,gid);
    printf("the group id of the file has been changed successfully\n");
}

void chowner(char * ownername,char * filename)
{
    struct passwd *password_info = NULL;
    if((password_info = getpwnam(ownername)) == NULL)
    {
        printf("username does not exist\n");
        return;
    }
    if(access(filename,F_OK) != 0)
    {
        printf("file %s does not exist\n",filename);
        return;
    }
    int uid = password_info->pw_uid;
    chown(filename,uid,-1);
    printf("the user id of the file has been changed successfully\n");
}

void _chmod(char * mod,char * filename)
{
    if(access(filename,F_OK) != 0)
        {
            printf("the file %s does not exist",filename);
            return;
        }

    int len = strlen(mod);
    switch(len)
        {
            case 1:
            {
                int a;
                a = mod[0] - '0';
                mode_t mode = 0;
                if(a < 0 || a > 7)
                    {
                        printf("octal number out of range\n");
                        return ;
                    }
                if(a & 0x04)
                    mode = mode | S_IROTH;
                if(a & 0x02)
                    mode = mode | S_IWOTH;
                if(a & 0x01)
                    mode = mode | S_IXOTH;
                chmod(filename,mode);
                printf("the mode has been changed successfully\n");
                break;
            }
            case 2:
            {
                int a,b;
                mode_t mode = 0;
                a = mod[0] - '0';
                b = mod[1] - '0';

                if(a < 0 || a > 7 || b < 0 || b > 7)
                    {
                        printf("octal number out of range\n");
                        return ;
                    }

                if(b & 0x04)
                    mode = mode | S_IROTH;
                if(b & 0x02)
                    mode = mode | S_IWOTH;
                if(b & 0x01)
                    mode = mode | S_IXOTH;

                if(a & 0x04)
                    mode = mode | S_IRGRP;
                if(a & 0x02)
                    mode = mode | S_IWGRP;
                if(a & 0x01)
                    mode = mode | S_IXGRP;
                chmod(filename,mode);
                printf("the mode has been changed successfully\n");
                break;
            }
            case 3:
            {
                int a,b,c;
                mode_t mode = 0;
                a = mod[0] - '0';
                b = mod[1] - '0';
                c = mod[2] - '0';

                if(a < 0 || a > 7 || b < 0 || b > 7 || c < 0 || c > 7)
                    {
                        printf("octal number out of range\n");
                        return ;
                    }


                if(a & 0x04)
                    mode = mode | S_IRUSR;
                if(a & 0x02)
                    mode = mode | S_IWUSR;
                if(a & 0x01)
                    mode = mode | S_IXUSR;

                if(b & 0x04)
                    mode = mode | S_IRGRP;
                if(b & 0x02)
                    mode = mode | S_IWGRP;
                if(b & 0x01)
                    mode = mode | S_IXGRP;

                if(c & 0x04)
                    mode = mode | S_IROTH;
                if(c & 0x02)
                    mode = mode | S_IWOTH;
                if(c & 0x01)
                    mode = mode | S_IXOTH;
                chmod(filename,mode);
                printf("the mode has been changed successfully\n");
                break;
            }
            default:
            {
                int a,b,c,d;
                mode_t mode = 0;
                a = mod[len-4] - '0';
                b = mod[len-3] - '0';
                c = mod[len-2] - '0';
                d = mod[len-1] - '0';

                if(a != 0 || b < 0 || b > 7 || c < 0 || c > 7 || d < 0 || d >7)
                    {
                        printf("octal number out of range\n");
                        return ;
                    }

                if(b & 0x04)
                    mode = mode | S_IRUSR;
                if(b & 0x02)
                    mode = mode | S_IWUSR;
                if(b & 0x01)
                    mode = mode | S_IXUSR;

                if(c & 0x04)
                    mode = mode | S_IRGRP;
                if(c & 0x02)
                    mode = mode | S_IWGRP;
                if(c & 0x01)
                    mode = mode | S_IXGRP;

                if(d & 0x04)
                    mode = mode | S_IROTH;
                if(d & 0x02)
                    mode = mode | S_IWOTH;
                if(d & 0x01)
                    mode = mode | S_IXOTH;
                chmod(filename,mode);
                printf("the mode has been changed successfully\n");
                break;
            }
        }
}

自己动手写shell之chgrp,chown,chmod