Working with the Unix OS

C Libraries
/* readdir: read directory entries in sequence */
#include /* local directory structure */
Dirent *readdir(DIR *dp)
{
struct direct dirbuf; /* local directory structure */
static Dirent d; /* return: portable structure */
}
while(read(dp->fd,(char*) &dirbuf, sizeof(dirbuf))== sizeof(dirbuf))
{
if (dirbuf.d_ino == 0) /* slot not in use */
continue;
d.ino = dirbuf.d_ino;
strncpy(d.name, dirbuf.d_name, DIRSIZ);
d.name[DIRSIZ] = '\0'; /* ensure termination */
return &d;
}
return NULL;
File Status and Control
int fstat(int fd, struct stat *status);
int link(char *origfile, char *newfile);
int chmod(char *filename, int accessmode);
int chdir(char *dirname); /* return 0 if successful */
int ioctl(int fd, int request, struct req *reqparams);
/* get and set line parameters (baud rate etc) */
System call I/O
User
function calls
values
Standard I/O
return
function calls Standard call return values
function calls UNIX kernel return values
Pipes
FILE *p; /* pipe stream */
char line[MAXLINE]; /* lines read */
if ((p = popen("grep unix *","r")) == NULL){
fprintf(stderr,"can't create pipe\n"); exit(1);
}
while (fgets(line,sizeof line, p) != EOF){
/* do something with line */
}
pclose(p); /* close the pipe */
Parallel execution
fork duplicates a process and sets both executing in parallel, where as exec allows process to hand over control to
another program. By combining fork and exec, one program may start a second program and continue executing
itself. The original is then called the parent process, the copy is called the child process and both exe in parallel.
system(char *command) /* execute a shell command*/
{
int status; /* status returned by command */
int pid; /* process id of command */
int wval; /* value returned by wait */
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