Modify to exit when the user types the command "exit" or when the program sees end of file. The code to be modified is:

/** prompting shell version 2 ** ** Solves the `one-shot' problem of version 1 ** Uses execvp(), but fork()s first so that the ** shell waits around to perform another command ** New problem: shell catches signals. Run vi, press ^c. **/

#include #include

#define MAXARGS 20 /* cmdline args */ #define ARGLEN 100 /* token length */

main() { char *arglist[MAXARGS+1]; /* an array of ptrs */ int numargs; /* index into array */ char argbuf[ARGLEN]; /* read stuff here */ char *makestring(); /* malloc etc */

numargs = 0; while ( numargs < MAXARGS ) { printf("Arg[%d]? ", numargs); if ( fgets(argbuf, ARGLEN, stdin) && *argbuf != ' ' ) arglist[numargs++] = makestring(argbuf); else { if ( numargs > 0 ){ /* any args? */ arglist[numargs]=NULL; /* close list */ execute( arglist ); /* do it */ numargs = 0; /* and reset */ } } } return 0; }

execute( char *arglist[] ) /* * use fork and execvp and wait to do it */ { int pid,exitstatus; /* of child */

pid = fork(); /* make new process */ switch( pid ){ case -1: perror("fork failed"); exit(1); case 0: execvp(arglist[0], arglist); /* do it */ perror("execvp failed"); exit(1); default: while( wait(&exitstatus) != pid ) ; printf("child exited with status %d,%d ", exitstatus>>8, exitstatus&0377); } } char *makestring( char *buf ) /* * trim off newline and create storage for the string */ { char *cp, *malloc();

buf[strlen(buf)-1] = '\0'; /* trim newline */ cp = malloc( strlen(buf)+1 ); /* get memory */ if ( cp == NULL ){ /* or die */ fprintf(stderr,"no memory "); exit(1); } strcpy(cp, buf); /* copy chars */ return cp; /* return ptr */ }