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#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>
#include <string.h>
 
#define MAXLINE 1024
void getCmd(char*);
void fork4aCmd(pid_t*, char*);
void wait4Child(pid_t*);
 
int main(void)
{
	char buf[MAXLINE];
	pid_t pid;
 
	printf("%% ");
	while(fgets(buf, MAXLINE, stdin) != NULL) {
		getCmd(buf);
		fork4aCmd(buf);
		wait4child(pid);
		printf("%%");
	}
	exit(0);
}
void getCmd(char *buf)
{
	if(buf[strlen(buf)-1] == '\n')
	buf[strlen(buf)-1] = 0;
	return;
}
 
void fork4aCmd(pid_t *pid, char *buf)
{
	if((*pid = fork()) < 0) {
		fprintf(stderr, "fork error!\n");
		exit(1);
	} else {
		execlp(buf, buf, (char*) 0);
		fprintf(stderr, "exec error!\n");
		exit(2);
	}
	return;
}
 
void wait4Child(pid_t *pid)
{
	int status;
	if((*pid = waitpid(*pid, &status, 0)) < 0){
		fprintf(stderr, "waitpid error!\n");
		exit(3);
	}
	return; 
} 

prog.c:9:16: error: unknown type name ‘pid_t’
 void fork4aCmd(pid_t*, char*);
                ^~~~~
prog.c:10:17: error: unknown type name ‘pid_t’
 void wait4Child(pid_t*);
                 ^~~~~
prog.c: In function ‘main’:
prog.c:15:2: error: unknown type name ‘pid_t’
  pid_t pid;
  ^~~~~
prog.c:20:3: warning: implicit declaration of function ‘fork4aCmd’ [-Wimplicit-function-declaration]
   fork4aCmd(buf);
   ^~~~~~~~~
prog.c:21:3: warning: implicit declaration of function ‘wait4child’ [-Wimplicit-function-declaration]
   wait4child(pid);
   ^~~~~~~~~~
prog.c: At top level:
prog.c:33:16: error: unknown type name ‘pid_t’
 void fork4aCmd(pid_t *pid, char *buf)
                ^~~~~
prog.c:46:17: error: unknown type name ‘pid_t’
 void wait4Child(pid_t *pid)
                 ^~~~~

Standard output is empty