#include <stdio.h>#include <grp.h>#include <pwd.h>struct	group	*getgrnam(), *grp;struct	passwd	*getpwuid(), *pwd;char	*getpass(), *crypt();main(argc,argv)int	argc;char	**argv;{	register i;	if(argc != 2) {		printf("usage: newgrp groupname\n");		done();	}	if((grp=getgrnam(argv[1])) == NULL) {		printf("%s: no such group\n", argv[1]);		done();	}	if((pwd=getpwuid(getuid())) == NULL) {		printf("You do not exist!\n");		done();	}	for(i=0;grp->gr_mem[i];i++) 		if(strcmp(grp->gr_mem[i], pwd->pw_name) == 0)			break;	if(grp->gr_mem[i] == 0 && strcmp(grp->gr_name,"other")) {		printf("Sorry\n");		done();	}	if(grp->gr_passwd[0] != '\0' && pwd->pw_passwd[0] == '\0') {		if(strcmp(grp->gr_passwd, crypt(getpass("Password:"),grp->gr_passwd)) != 0) {			printf("Sorry\n");			done();		}	}	if(setgid(grp->gr_gid) < 0)		perror("setgid");	done();}done(){	register i;	setuid(getuid());	for (i=3; i<15; i++)		close(i);	execl("/bin/sh", "sh", 0);	printf("No shell!\n");	exit(0);}