xref: /freebsd/usr.bin/xargs/xargs.c (revision af23369a6deaaeb612ab266eb88b8bb8d560c322)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1990, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * This code is derived from software contributed to Berkeley by
8  * John B. Roll Jr.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. Neither the name of the University nor the names of its contributors
19  *    may be used to endorse or promote products derived from this software
20  *    without specific prior written permission.
21  *
22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32  * SUCH DAMAGE.
33  *
34  * $xMach: xargs.c,v 1.6 2002/02/23 05:27:47 tim Exp $
35  */
36 
37 #if 0
38 #ifndef lint
39 static const char copyright[] =
40 "@(#) Copyright (c) 1990, 1993\n\
41 	The Regents of the University of California.  All rights reserved.\n";
42 #endif /* not lint */
43 
44 #ifndef lint
45 static char sccsid[] = "@(#)xargs.c	8.1 (Berkeley) 6/6/93";
46 #endif /* not lint */
47 #endif
48 #include <sys/cdefs.h>
49 __FBSDID("$FreeBSD$");
50 
51 #include <sys/types.h>
52 #include <sys/wait.h>
53 #include <sys/time.h>
54 #include <sys/limits.h>
55 #include <sys/resource.h>
56 #include <err.h>
57 #include <errno.h>
58 #include <fcntl.h>
59 #include <getopt.h>
60 #include <langinfo.h>
61 #include <locale.h>
62 #include <paths.h>
63 #include <regex.h>
64 #include <stdbool.h>
65 #include <stdio.h>
66 #include <stdlib.h>
67 #include <string.h>
68 #include <unistd.h>
69 
70 #include "pathnames.h"
71 
72 static void	parse_input(int, char *[]);
73 static void	prerun(int, char *[]);
74 static int	prompt(void);
75 static void	run(char **);
76 static void	usage(void);
77 bool		strnsubst(char **, const char *, const char *, size_t);
78 static pid_t	xwait(int block, int *status);
79 static void	xexit(const char *, const int);
80 static void	waitchildren(const char *, int);
81 static void	pids_init(void);
82 static int	pids_empty(void);
83 static int	pids_full(void);
84 static void	pids_add(pid_t pid);
85 static int	pids_remove(pid_t pid);
86 static int	findslot(pid_t pid);
87 static int	findfreeslot(void);
88 static void	clearslot(int slot);
89 
90 static char echo[] = _PATH_ECHO;
91 static char **av, **bxp, **ep, **endxp, **xp;
92 static char *argp, *bbp, *ebp, *inpline, *p, *replstr;
93 static const char *eofstr;
94 static int count, insingle, indouble, oflag, pflag, tflag, Rflag, rval, zflag;
95 static int cnt, Iflag, jfound, Lflag, Sflag, wasquoted, xflag;
96 static int curprocs, maxprocs;
97 static pid_t *childpids;
98 
99 static volatile int childerr;
100 
101 extern char **environ;
102 
103 static const char *optstr = "+0E:I:J:L:n:oP:pR:S:s:rtx";
104 
105 static const struct option long_options[] =
106 {
107 	{"exit",		no_argument,		NULL,	'x'},
108 	{"interactive",		no_argument,		NULL,	'p'},
109 	{"max-args",		required_argument,	NULL,	'n'},
110 	{"max-chars",		required_argument,	NULL,	's'},
111 	{"max-procs",		required_argument,	NULL,	'P'},
112 	{"no-run-if-empty",	no_argument,		NULL,	'r'},
113 	{"null",		no_argument,		NULL,	'0'},
114 	{"verbose",		no_argument,		NULL,	't'},
115 
116 	{NULL,			no_argument,		NULL,	0},
117 };
118 
119 int
120 main(int argc, char *argv[])
121 {
122 	long arg_max;
123 	int ch, Jflag, nargs, nflag, nline;
124 	size_t linelen;
125 	struct rlimit rl;
126 	char *endptr;
127 	const char *errstr;
128 
129 	inpline = replstr = NULL;
130 	ep = environ;
131 	eofstr = "";
132 	Jflag = nflag = 0;
133 
134 	(void)setlocale(LC_ALL, "");
135 
136 	/*
137 	 * POSIX.2 limits the exec line length to ARG_MAX - 2K.  Running that
138 	 * caused some E2BIG errors, so it was changed to ARG_MAX - 4K.  Given
139 	 * that the smallest argument is 2 bytes in length, this means that
140 	 * the number of arguments is limited to:
141 	 *
142 	 *	 (ARG_MAX - 4K - LENGTH(utility + arguments)) / 2.
143 	 *
144 	 * We arbitrarily limit the number of arguments to 5000.  This is
145 	 * allowed by POSIX.2 as long as the resulting minimum exec line is
146 	 * at least LINE_MAX.  Realloc'ing as necessary is possible, but
147 	 * probably not worthwhile.
148 	 */
149 	nargs = 5000;
150 	if ((arg_max = sysconf(_SC_ARG_MAX)) == -1)
151 		errx(1, "sysconf(_SC_ARG_MAX) failed");
152 	nline = arg_max - 4 * 1024;
153 	while (*ep != NULL) {
154 		/* 1 byte for each '\0' */
155 		nline -= strlen(*ep++) + 1 + sizeof(*ep);
156 	}
157 	maxprocs = 1;
158 	while ((ch = getopt_long(argc, argv, optstr, long_options, NULL)) != -1)
159 		switch (ch) {
160 		case 'E':
161 			eofstr = optarg;
162 			break;
163 		case 'I':
164 			Jflag = 0;
165 			Iflag = 1;
166 			Lflag = 1;
167 			replstr = optarg;
168 			break;
169 		case 'J':
170 			Iflag = 0;
171 			Jflag = 1;
172 			replstr = optarg;
173 			break;
174 		case 'L':
175 			Lflag = strtonum(optarg, 0, INT_MAX, &errstr);
176 			if (errstr)
177 				errx(1, "-L %s: %s", optarg, errstr);
178 			break;
179 		case 'n':
180 			nflag = 1;
181 			nargs = strtonum(optarg, 1, INT_MAX, &errstr);
182 			if (errstr)
183 				errx(1, "-n %s: %s", optarg, errstr);
184 			break;
185 		case 'o':
186 			oflag = 1;
187 			break;
188 		case 'P':
189 			maxprocs = strtonum(optarg, 0, INT_MAX, &errstr);
190 			if (errstr)
191 				errx(1, "-P %s: %s", optarg, errstr);
192 			if (getrlimit(RLIMIT_NPROC, &rl) != 0)
193 				errx(1, "getrlimit failed");
194 			if (maxprocs == 0 || maxprocs > rl.rlim_cur)
195 				maxprocs = rl.rlim_cur;
196 			break;
197 		case 'p':
198 			pflag = 1;
199 			break;
200 		case 'R':
201 			Rflag = strtol(optarg, &endptr, 10);
202 			if (*endptr != '\0')
203 				errx(1, "replacements must be a number");
204 			break;
205 		case 'r':
206 			/* GNU compatibility */
207 			break;
208 		case 'S':
209 			Sflag = strtoul(optarg, &endptr, 10);
210 			if (*endptr != '\0')
211 				errx(1, "replsize must be a number");
212 			break;
213 		case 's':
214 			nline = strtonum(optarg, 0, INT_MAX, &errstr);
215 			if (errstr)
216 				errx(1, "-s %s: %s", optarg, errstr);
217 			break;
218 		case 't':
219 			tflag = 1;
220 			break;
221 		case 'x':
222 			xflag = 1;
223 			break;
224 		case '0':
225 			zflag = 1;
226 			break;
227 		case '?':
228 		default:
229 			usage();
230 	}
231 	argc -= optind;
232 	argv += optind;
233 
234 	if (!Iflag && Rflag)
235 		usage();
236 	if (!Iflag && Sflag)
237 		usage();
238 	if (Iflag && !Rflag)
239 		Rflag = 5;
240 	if (Iflag && !Sflag)
241 		Sflag = 255;
242 	if (xflag && !nflag)
243 		usage();
244 	if (Iflag || Lflag)
245 		xflag = 1;
246 	if (replstr != NULL && *replstr == '\0')
247 		errx(1, "replstr may not be empty");
248 
249 	pids_init();
250 
251 	/*
252 	 * Allocate pointers for the utility name, the utility arguments,
253 	 * the maximum arguments to be read from stdin and the trailing
254 	 * NULL.
255 	 */
256 	linelen = 1 + argc + nargs + 1;
257 	if ((av = bxp = malloc(linelen * sizeof(char *))) == NULL)
258 		errx(1, "malloc failed");
259 
260 	/*
261 	 * Use the user's name for the utility as argv[0], just like the
262 	 * shell.  Echo is the default.  Set up pointers for the user's
263 	 * arguments.
264 	 */
265 	if (*argv == NULL)
266 		cnt = strlen(*bxp++ = echo);
267 	else {
268 		do {
269 			if (Jflag && strcmp(*argv, replstr) == 0) {
270 				char **avj;
271 				jfound = 1;
272 				argv++;
273 				for (avj = argv; *avj; avj++)
274 					cnt += strlen(*avj) + 1;
275 				break;
276 			}
277 			cnt += strlen(*bxp++ = *argv) + 1;
278 		} while (*++argv != NULL);
279 	}
280 
281 	/*
282 	 * Set up begin/end/traversing pointers into the array.  The -n
283 	 * count doesn't include the trailing NULL pointer, so the malloc
284 	 * added in an extra slot.
285 	 */
286 	endxp = (xp = bxp) + nargs;
287 
288 	/*
289 	 * Allocate buffer space for the arguments read from stdin and the
290 	 * trailing NULL.  Buffer space is defined as the default or specified
291 	 * space, minus the length of the utility name and arguments.  Set up
292 	 * begin/end/traversing pointers into the array.  The -s count does
293 	 * include the trailing NULL, so the malloc didn't add in an extra
294 	 * slot.
295 	 */
296 	nline -= cnt;
297 	if (nline <= 0)
298 		errx(1, "insufficient space for command");
299 
300 	if ((bbp = malloc((size_t)(nline + 1))) == NULL)
301 		errx(1, "malloc failed");
302 	ebp = (argp = p = bbp) + nline - 1;
303 	for (;;)
304 		parse_input(argc, argv);
305 }
306 
307 static void
308 parse_input(int argc, char *argv[])
309 {
310 	int ch, foundeof;
311 	char **avj;
312 
313 	foundeof = 0;
314 
315 	switch (ch = getchar()) {
316 	case EOF:
317 		/* No arguments since last exec. */
318 		if (p == bbp) {
319 			waitchildren(*av, 1);
320 			exit(rval);
321 		}
322 		goto arg1;
323 	case ' ':
324 	case '\t':
325 		/* Quotes escape tabs and spaces. */
326 		if (insingle || indouble || zflag)
327 			goto addch;
328 		goto arg2;
329 	case '\0':
330 		if (zflag) {
331 			/*
332 			 * Increment 'count', so that nulls will be treated
333 			 * as end-of-line, as well as end-of-argument.  This
334 			 * is needed so -0 works properly with -I and -L.
335 			 */
336 			count++;
337 			goto arg2;
338 		}
339 		goto addch;
340 	case '\n':
341 		if (zflag)
342 			goto addch;
343 		count++;	    /* Indicate end-of-line (used by -L) */
344 
345 		/* Quotes do not escape newlines. */
346 arg1:		if (insingle || indouble) {
347 			warnx("unterminated quote");
348 			xexit(*av, 1);
349 		}
350 arg2:
351 		foundeof = *eofstr != '\0' &&
352 		    strncmp(argp, eofstr, p - argp) == 0;
353 
354 		/* Do not make empty args unless they are quoted */
355 		if ((argp != p || wasquoted) && !foundeof) {
356 			*p++ = '\0';
357 			*xp++ = argp;
358 			if (Iflag) {
359 				size_t curlen;
360 
361 				if (inpline == NULL)
362 					curlen = 0;
363 				else {
364 					/*
365 					 * If this string is not zero
366 					 * length, append a space for
367 					 * separation before the next
368 					 * argument.
369 					 */
370 					if ((curlen = strlen(inpline)))
371 						strcat(inpline, " ");
372 				}
373 				curlen++;
374 				/*
375 				 * Allocate enough to hold what we will
376 				 * be holding in a second, and to append
377 				 * a space next time through, if we have
378 				 * to.
379 				 */
380 				inpline = realloc(inpline, curlen + 2 +
381 				    strlen(argp));
382 				if (inpline == NULL) {
383 					warnx("realloc failed");
384 					xexit(*av, 1);
385 				}
386 				if (curlen == 1)
387 					strcpy(inpline, argp);
388 				else
389 					strcat(inpline, argp);
390 			}
391 		}
392 
393 		/*
394 		 * If max'd out on args or buffer, or reached EOF,
395 		 * run the command.  If xflag and max'd out on buffer
396 		 * but not on args, object.  Having reached the limit
397 		 * of input lines, as specified by -L is the same as
398 		 * maxing out on arguments.
399 		 */
400 		if (xp == endxp || p > ebp || ch == EOF ||
401 		    (Lflag <= count && xflag) || foundeof) {
402 			if (xflag && xp != endxp && p > ebp) {
403 				warnx("insufficient space for arguments");
404 				xexit(*av, 1);
405 			}
406 			if (jfound) {
407 				for (avj = argv; *avj; avj++)
408 					*xp++ = *avj;
409 			}
410 			prerun(argc, av);
411 			if (ch == EOF || foundeof) {
412 				waitchildren(*av, 1);
413 				exit(rval);
414 			}
415 			p = bbp;
416 			xp = bxp;
417 			count = 0;
418 		}
419 		argp = p;
420 		wasquoted = 0;
421 		break;
422 	case '\'':
423 		if (indouble || zflag)
424 			goto addch;
425 		insingle = !insingle;
426 		wasquoted = 1;
427 		break;
428 	case '"':
429 		if (insingle || zflag)
430 			goto addch;
431 		indouble = !indouble;
432 		wasquoted = 1;
433 		break;
434 	case '\\':
435 		if (zflag)
436 			goto addch;
437 		/* Backslash escapes anything, is escaped by quotes. */
438 		if (!insingle && !indouble && (ch = getchar()) == EOF) {
439 			warnx("backslash at EOF");
440 			xexit(*av, 1);
441 		}
442 		/* FALLTHROUGH */
443 	default:
444 addch:		if (p < ebp) {
445 			*p++ = ch;
446 			break;
447 		}
448 
449 		/* If only one argument, not enough buffer space. */
450 		if (bxp == xp) {
451 			warnx("insufficient space for argument");
452 			xexit(*av, 1);
453 		}
454 		/* Didn't hit argument limit, so if xflag object. */
455 		if (xflag) {
456 			warnx("insufficient space for arguments");
457 			xexit(*av, 1);
458 		}
459 
460 		if (jfound) {
461 			for (avj = argv; *avj; avj++)
462 				*xp++ = *avj;
463 		}
464 		prerun(argc, av);
465 		xp = bxp;
466 		cnt = ebp - argp;
467 		memcpy(bbp, argp, (size_t)cnt);
468 		p = (argp = bbp) + cnt;
469 		*p++ = ch;
470 		break;
471 	}
472 }
473 
474 /*
475  * Do things necessary before run()'ing, such as -I substitution,
476  * and then call run().
477  */
478 static void
479 prerun(int argc, char *argv[])
480 {
481 	char **tmp, **tmp2, **avj;
482 	int repls;
483 
484 	repls = Rflag;
485 
486 	if (argc == 0 || repls == 0) {
487 		*xp = NULL;
488 		run(argv);
489 		return;
490 	}
491 
492 	avj = argv;
493 
494 	/*
495 	 * Allocate memory to hold the argument list, and
496 	 * a NULL at the tail.
497 	 */
498 	tmp = malloc((argc + 1) * sizeof(char *));
499 	if (tmp == NULL) {
500 		warnx("malloc failed");
501 		xexit(*argv, 1);
502 	}
503 	tmp2 = tmp;
504 
505 	/*
506 	 * Save the first argument and iterate over it, we
507 	 * cannot do strnsubst() to it.
508 	 */
509 	if ((*tmp++ = strdup(*avj++)) == NULL) {
510 		warnx("strdup failed");
511 		xexit(*argv, 1);
512 	}
513 
514 	/*
515 	 * For each argument to utility, if we have not used up
516 	 * the number of replacements we are allowed to do, and
517 	 * if the argument contains at least one occurrence of
518 	 * replstr, call strnsubst(), else just save the string.
519 	 * Iterations over elements of avj and tmp are done
520 	 * where appropriate.
521 	 */
522 	while (--argc) {
523 		*tmp = *avj++;
524 		if (repls && strstr(*tmp, replstr) != NULL) {
525 			if (strnsubst(tmp++, replstr, inpline, (size_t)Sflag)) {
526 				warnx("comamnd line cannot be assembled, too long");
527 				xexit(*argv, 1);
528 			}
529 			if (repls > 0)
530 				repls--;
531 		} else {
532 			if ((*tmp = strdup(*tmp)) == NULL) {
533 				warnx("strdup failed");
534 				xexit(*argv, 1);
535 			}
536 			tmp++;
537 		}
538 	}
539 
540 	/*
541 	 * Run it.
542 	 */
543 	*tmp = NULL;
544 	run(tmp2);
545 
546 	/*
547 	 * Walk from the tail to the head, free along the way.
548 	 */
549 	for (; tmp2 != tmp; tmp--)
550 		free(*tmp);
551 	/*
552 	 * Now free the list itself.
553 	 */
554 	free(tmp2);
555 
556 	/*
557 	 * Free the input line buffer, if we have one.
558 	 */
559 	if (inpline != NULL) {
560 		free(inpline);
561 		inpline = NULL;
562 	}
563 }
564 
565 static void
566 run(char **argv)
567 {
568 	pid_t pid;
569 	int fd;
570 	char **avec;
571 
572 	/*
573 	 * If the user wants to be notified of each command before it is
574 	 * executed, notify them.  If they want the notification to be
575 	 * followed by a prompt, then prompt them.
576 	 */
577 	if (tflag || pflag) {
578 		(void)fprintf(stderr, "%s", *argv);
579 		for (avec = argv + 1; *avec != NULL; ++avec)
580 			(void)fprintf(stderr, " %s", *avec);
581 		/*
582 		 * If the user has asked to be prompted, do so.
583 		 */
584 		if (pflag)
585 			/*
586 			 * If they asked not to exec, return without execution
587 			 * but if they asked to, go to the execution.  If we
588 			 * could not open their tty, break the switch and drop
589 			 * back to -t behaviour.
590 			 */
591 			switch (prompt()) {
592 			case 0:
593 				return;
594 			case 1:
595 				goto exec;
596 			case 2:
597 				break;
598 			}
599 		(void)fprintf(stderr, "\n");
600 		(void)fflush(stderr);
601 	}
602 exec:
603 	childerr = 0;
604 	switch (pid = vfork()) {
605 	case -1:
606 		warn("vfork");
607 		xexit(*argv, 1);
608 	case 0:
609 		if (oflag) {
610 			if ((fd = open(_PATH_TTY, O_RDONLY)) == -1)
611 				err(1, "can't open /dev/tty");
612 		} else {
613 			fd = open(_PATH_DEVNULL, O_RDONLY);
614 		}
615 		if (fd > STDIN_FILENO) {
616 			if (dup2(fd, STDIN_FILENO) != 0)
617 				err(1, "can't dup2 to stdin");
618 			close(fd);
619 		}
620 		execvp(argv[0], argv);
621 		childerr = errno;
622 		_exit(1);
623 	}
624 	pids_add(pid);
625 	waitchildren(*argv, 0);
626 }
627 
628 /*
629  * Wait for a tracked child to exit and return its pid and exit status.
630  *
631  * Ignores (discards) all untracked child processes.
632  * Returns -1 and sets errno to ECHILD if no tracked children exist.
633  * If block is set, waits indefinitely for a child process to exit.
634  * If block is not set and no children have exited, returns 0 immediately.
635  */
636 static pid_t
637 xwait(int block, int *status) {
638 	pid_t pid;
639 
640 	if (pids_empty()) {
641 		errno = ECHILD;
642 		return (-1);
643 	}
644 
645 	while ((pid = waitpid(-1, status, block ? 0 : WNOHANG)) > 0)
646 		if (pids_remove(pid))
647 			break;
648 
649 	return (pid);
650 }
651 
652 static void
653 xexit(const char *name, const int exit_code) {
654 	waitchildren(name, 1);
655 	exit(exit_code);
656 }
657 
658 static void
659 waitchildren(const char *name, int waitall)
660 {
661 	pid_t pid;
662 	int status;
663 	int cause_exit = 0;
664 
665 	while ((pid = xwait(waitall || pids_full(), &status)) > 0) {
666 		/*
667 		 * If we couldn't invoke the utility or if utility exited
668 		 * because of a signal or with a value of 255, warn (per
669 		 * POSIX), and then wait until all other children have
670 		 * exited before exiting 1-125. POSIX requires us to stop
671 		 * reading if child exits because of a signal or with 255,
672 		 * but it does not require us to exit immediately; waiting
673 		 * is preferable to orphaning.
674 		 */
675 		if (childerr != 0 && cause_exit == 0) {
676 			errno = childerr;
677 			waitall = 1;
678 			cause_exit = errno == ENOENT ? 127 : 126;
679 			warn("%s", name);
680 		} else if (WIFSIGNALED(status)) {
681 			waitall = cause_exit = 1;
682 			warnx("%s: terminated with signal %d; aborting",
683 			    name, WTERMSIG(status));
684 		} else if (WEXITSTATUS(status) == 255) {
685 			waitall = cause_exit = 1;
686 			warnx("%s: exited with status 255; aborting", name);
687 		} else if (WEXITSTATUS(status))
688  			rval = 1;
689 	}
690 
691  	if (cause_exit)
692 		exit(cause_exit);
693 	if (pid == -1 && errno != ECHILD)
694 		err(1, "waitpid");
695 }
696 
697 #define	NOPID	(0)
698 
699 static void
700 pids_init(void)
701 {
702 	int i;
703 
704 	if ((childpids = malloc(maxprocs * sizeof(*childpids))) == NULL)
705 		errx(1, "malloc failed");
706 
707 	for (i = 0; i < maxprocs; i++)
708 		clearslot(i);
709 }
710 
711 static int
712 pids_empty(void)
713 {
714 
715 	return (curprocs == 0);
716 }
717 
718 static int
719 pids_full(void)
720 {
721 
722 	return (curprocs >= maxprocs);
723 }
724 
725 static void
726 pids_add(pid_t pid)
727 {
728 	int slot;
729 
730 	slot = findfreeslot();
731 	childpids[slot] = pid;
732 	curprocs++;
733 }
734 
735 static int
736 pids_remove(pid_t pid)
737 {
738 	int slot;
739 
740 	if ((slot = findslot(pid)) < 0)
741 		return (0);
742 
743 	clearslot(slot);
744 	curprocs--;
745 	return (1);
746 }
747 
748 static int
749 findfreeslot(void)
750 {
751 	int slot;
752 
753 	if ((slot = findslot(NOPID)) < 0)
754 		errx(1, "internal error: no free pid slot");
755 	return (slot);
756 }
757 
758 static int
759 findslot(pid_t pid)
760 {
761 	int slot;
762 
763 	for (slot = 0; slot < maxprocs; slot++)
764 		if (childpids[slot] == pid)
765 			return (slot);
766 	return (-1);
767 }
768 
769 static void
770 clearslot(int slot)
771 {
772 
773 	childpids[slot] = NOPID;
774 }
775 
776 /*
777  * Prompt the user about running a command.
778  */
779 static int
780 prompt(void)
781 {
782 	regex_t cre;
783 	size_t rsize;
784 	int match;
785 	char *response;
786 	FILE *ttyfp;
787 
788 	if ((ttyfp = fopen(_PATH_TTY, "r")) == NULL)
789 		return (2);	/* Indicate that the TTY failed to open. */
790 	(void)fprintf(stderr, "?...");
791 	(void)fflush(stderr);
792 	if ((response = fgetln(ttyfp, &rsize)) == NULL ||
793 	    regcomp(&cre, nl_langinfo(YESEXPR), REG_EXTENDED) != 0) {
794 		(void)fclose(ttyfp);
795 		return (0);
796 	}
797 	response[rsize - 1] = '\0';
798 	match = regexec(&cre, response, 0, NULL, 0);
799 	(void)fclose(ttyfp);
800 	regfree(&cre);
801 	return (match == 0);
802 }
803 
804 static void
805 usage(void)
806 {
807 
808 	fprintf(stderr,
809 "usage: xargs [-0opt] [-E eofstr] [-I replstr [-R replacements] [-S replsize]]\n"
810 "             [-J replstr] [-L number] [-n number [-x]] [-P maxprocs]\n"
811 "             [-s size] [utility [argument ...]]\n");
812 	exit(1);
813 }
814