/* *	Public Domain simplified version of the System V xargs program. * *	Author:	Andrew Gollan */#include	<sys/param.h>#include	<stdio.h>/* *	Handle the ATT/BSD ideas of wait(2). */#ifdef	BSD#include	<sys/wait.h>typedef union wait	WAIT_T;#elsetypedef	int		WAIT_T;#endif	/* BSD *//* *	Set the maximum argument list that xargs will generate. *	The reason this is not just NCARGS is that NCARGS can include *	the environment space as well, a really serious program would *	size the environment on the fly (but you know what you can do *	with that idea). This is pretty big and pretty safe. * *	Also set the maximum number of arguments that we are going to cope with. *	This needed so that we can allocate an array of char * for execv(). Note *	that on (at least some) BSD systems NCARGS is 1MB and MAXNARGS will be *	32K. Thank the powers for virtual memory. */#define	MAXCARGS	(NCARGS / 2)#define	MAXNARGS	(MAXCARGS / 32)/* *	We need to set a limit on an input line for fgets, so use the *	longest pathname the system can cope with if available, otherwise *	a suitably large number. */#ifdef	MAXPATHLEN#define	MAXARGLEN	MAXPATHLEN#else#define	MAXARGLEN	1024#endif	/* MAXPATHLEN *//* *	System error handling. */#define	SYSERROR	(-1)extern int	errno;extern int	sys_nerr;extern char	*sys_errlist[];#define	sysmess()	(\				(errno < 0 || errno > sys_nerr) \				? \				"Unknown Error" \				: \				sys_errlist[errno] \			)/* *	Statically allocate (in the bss segment) an argument vector *	and a pool for collecting the arguments in. */static char	*argvector[MAXNARGS];static char	arglist[MAXCARGS];static int	argbase;/* *	Program name for error messages. */static char	*myname;/* *	Read lines from the standard input and pass them on as arguments *	to the provided command, making sure that the system limit on *	the number of characters in an argument is not exceeded. */int	xargs(){	/*	 *	Keep reading while the standard input is valid.	 */	while (!(feof(stdin) || ferror(stdin)))	{		register int	i;		register int	pid;		register char	*argptr	= arglist;		/*		 *	Limit the number of discrete arguments to MAXNARGS - 1.		 *	We need the last slot for a NULL pointer to keep		 *	execvp(2) happy.		 */		for (i = argbase; i < MAXNARGS - 1; ++i)		{			register int	len;			/*			 *	If we may run out of space or we get			 *	EOF or an error on input, stop collecting			 *	arguments.			 */			if			(				argptr + MAXARGLEN >= &arglist[MAXCARGS]				||				fgets(argptr, MAXARGLEN, stdin) == NULL			)				break;						/*			 *	Ignore empty arguments. Note that fgets leaves			 *	the newline at the end of the string.			 */			if ((len = strlen(argptr)) <= 1)				continue;			/*			 *	Kill the trailing newline, add this argument to			 *	the vector and advance the buffer pointer.			 */			argptr[len - 1] = '\0';			argvector[i] = argptr;			argptr += len;		}		/*		 *	Only run the command if we have some arguments.		 */		if (i <= argbase)			break;		/*		 *	Cap the vector with the NULL pointer needed for		 *	execvp(2).		 */		argvector[i] = NULL;		/*		 *	Fork and exec the command with all the collected		 *	arguments. Watch out for failed forks.		 */		switch (pid = fork())		{		case SYSERROR:			(void)fprintf			(				stderr,				"%s: Couldn't fork: %s\n",				myname,				sysmess()			);			exit(1);			/* NOTREACHED */		case 0:			/*			 *	The child just execs the command.			 */			(void)execvp(argvector[0], argvector);			perror(argvector[0]);			exit(1);		default:			/*			 *	Wait for the child to return. Due			 *	to shell handling of pipelines, it			 *	is possible to get the pid back from wait().			 */			while (wait((WAIT_T *)0) != pid)				;		}	}	return 0;}/* *	Process the arguments and call xargs(). */int	main(argc, argv)int	argc;char	*argv[];{	register int	i;	/*	 *	Get the program invocation name for error messages.	 */	myname = argv[0];	/*	 *	Check the arguments for consistency.	 */	if (argc < 2)	{		(void)fprintf(stderr, "usage: %s command [arg] ...\n", myname);		exit(1);	}	/*	 *	Fill in the command.	 */	for (i = 1; i < argc; ++i)		argvector[argbase++] = argv[i];	/*	 *	Call xargs() to do the real work.	 */	return xargs();}