shell/shell_common.c - codeaurora/busybox - Gitiles

 /* vi: set sw=4 ts=4: */
 /*
  * Adapted from ash applet code
  *
  * This code is derived from software contributed to Berkeley by
  * Kenneth Almquist.
  *
  * Copyright (c) 1989, 1991, 1993, 1994
  *      The Regents of the University of California.  All rights reserved.
  *
  * Copyright (c) 1997-2005 Herbert Xu <herbert@gondor.apana.org.au>
  * was re-ported from NetBSD and debianized.
  *
  * Copyright (c) 2010 Denys Vlasenko
  * Split from ash.c
  *
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
 #include "libbb.h"
 #include "shell_common.h"

 const char defifsvar[] ALIGN1 = "IFS= \t\n";
 const char defoptindvar[] ALIGN1 = "OPTIND=1";

 /* read builtin */

 /* Needs to be interruptible: shell must handle traps and shell-special signals
  * while inside read. To implement this, be sure to not loop on EINTR
  * and return errno == EINTR reliably.
  */
 //TODO: use more efficient setvar() which takes a pointer to malloced "VAR=VAL"
 //string. hush naturally has it, and ash has setvareq().
 //Here we can simply store "VAR=" at buffer start and store read data directly
 //after "=", then pass buffer to setvar() to consume.
 const char* FAST_FUNC
 shell_builtin_read(struct builtin_read_params *params)
 {
 	struct pollfd pfd[1];
 #define fd (pfd[0].fd) /* -u FD */
 	unsigned err;
 	unsigned end_ms; /* -t TIMEOUT */
 	int nchars; /* -n NUM */
 	char **pp;
 	char *buffer;
 	char delim;
 	struct termios tty, old_tty;
 	const char *retval;
 	int bufpos; /* need to be able to hold -1 */
 	int startword;
 	smallint backslash;
 	char **argv;
 	const char *ifs;
 	int read_flags;

 	errno = err = 0;

 	argv = params->argv;
 	pp = argv;
 	while (*pp) {
 		if (endofname(*pp)[0] != '\0') {
 			/* Mimic bash message */
 			bb_error_msg("read: '%s': bad variable name", *pp);
 			return (const char *)(uintptr_t)1;
 		}
 		pp++;
 	}

 	nchars = 0; /* if != 0, -n is in effect */
 	if (params->opt_n) {
 		nchars = bb_strtou(params->opt_n, NULL, 10);
 		if (nchars < 0 || errno)
 			return "invalid count";
 		/* note: "-n 0": off (bash 3.2 does this too) */
 	}

 	end_ms = 0;
 	if (params->opt_t && !ENABLE_FEATURE_SH_READ_FRAC) {
 		end_ms = bb_strtou(params->opt_t, NULL, 10);
 		if (errno)
 			return "invalid timeout";
 		if (end_ms > UINT_MAX / 2048) /* be safely away from overflow */
 			end_ms = UINT_MAX / 2048;
 		end_ms *= 1000;
 	}
 	if (params->opt_t && ENABLE_FEATURE_SH_READ_FRAC) {
 		/* bash 4.3 (maybe earlier) supports -t N.NNNNNN */
 		char *p;
 		/* Eat up to three fractional digits */
 		int frac_digits = 3 + 1;

 		end_ms = bb_strtou(params->opt_t, &p, 10);
 		if (end_ms > UINT_MAX / 2048) /* be safely away from overflow */
 			end_ms = UINT_MAX / 2048;

 		if (errno) {
 			/* EINVAL = number is ok, but not NUL terminated */
 			if (errno != EINVAL || *p != '.')
 				return "invalid timeout";
 			/* Do not check the rest: bash allows "0.123456xyz" */
 			while (*++p && --frac_digits) {
 				end_ms *= 10;
 				end_ms += (*p - '0');
 				if ((unsigned char)(*p - '0') > 9)
 					return "invalid timeout";
 			}
 		}
 		while (--frac_digits > 0) {
 			end_ms *= 10;
 		}
 	}

 	fd = STDIN_FILENO;
 	if (params->opt_u) {
 		fd = bb_strtou(params->opt_u, NULL, 10);
 		if (fd < 0 || errno)
 			return "invalid file descriptor";
 	}

 	if (params->opt_t && end_ms == 0) {
 		/* "If timeout is 0, read returns immediately, without trying
 		 * to read any data. The exit status is 0 if input is available
 		 * on the specified file descriptor, non-zero otherwise."
 		 * bash seems to ignore -p PROMPT for this use case.
 		 */
 		int r;
 		pfd[0].events = POLLIN;
 		r = poll(pfd, 1, /*timeout:*/ 0);
 		/* Return 0 only if poll returns 1 ("one fd ready"), else return 1: */
 		return (const char *)(uintptr_t)(r <= 0);
 	}

 	if (params->opt_p && isatty(fd)) {
 		fputs(params->opt_p, stderr);
 		fflush_all();
 	}

 	ifs = params->ifs;
 	if (ifs == NULL)
 		ifs = defifs;

 	read_flags = params->read_flags;
 	if (nchars || (read_flags & BUILTIN_READ_SILENT)) {
 		tcgetattr(fd, &tty);
 		old_tty = tty;
 		if (nchars) {
 			tty.c_lflag &= ~ICANON;
 			// Setting it to more than 1 breaks poll():
 			// it blocks even if there's data. !??
 			//tty.c_cc[VMIN] = nchars < 256 ? nchars : 255;
 			/* reads will block only if < 1 char is available */
 			tty.c_cc[VMIN] = 1;
 			/* no timeout (reads block forever) */
 			tty.c_cc[VTIME] = 0;
 		}
 		if (read_flags & BUILTIN_READ_SILENT) {
 			tty.c_lflag &= ~(ECHO | ECHOK | ECHONL);
 		}
 		/* This forces execution of "restoring" tcgetattr later */
 		read_flags |= BUILTIN_READ_SILENT;
 		/* if tcgetattr failed, tcsetattr will fail too.
 		 * Ignoring, it's harmless. */
 		tcsetattr(fd, TCSANOW, &tty);
 	}

 	retval = (const char *)(uintptr_t)0;
 	startword = 1;
 	backslash = 0;
 	if (params->opt_t)
 		end_ms += (unsigned)monotonic_ms();
 	buffer = NULL;
 	bufpos = 0;
 	delim = params->opt_d ? params->opt_d[0] : '\n';
 	do {
 		char c;
 		int timeout;

 		if ((bufpos & 0xff) == 0)
 			buffer = xrealloc(buffer, bufpos + 0x101);

 		timeout = -1;
 		if (params->opt_t) {
 			timeout = end_ms - (unsigned)monotonic_ms();
 			/* ^^^^^^^^^^^^^ all values are unsigned,
 			 * wrapping math is used here, good even if
 			 * 32-bit unix time wrapped (year 2038+).
 			 */
 			if (timeout <= 0) { /* already late? */
 				retval = (const char *)(uintptr_t)1;
 				goto ret;
 			}
 		}

 		/* We must poll even if timeout is -1:
 		 * we want to be interrupted if signal arrives,
 		 * regardless of SA_RESTART-ness of that signal!
 		 */
 		errno = 0;
 		pfd[0].events = POLLIN;
 //TODO race with a signal arriving just before the poll!
 		if (poll(pfd, 1, timeout) <= 0) {
 			/* timed out, or EINTR */
 			err = errno;
 			retval = (const char *)(uintptr_t)1;
 			goto ret;
 		}
 		if (read(fd, &buffer[bufpos], 1) != 1) {
 			err = errno;
 			retval = (const char *)(uintptr_t)1;
 			break;
 		}

 		c = buffer[bufpos];
 		if (!(read_flags & BUILTIN_READ_RAW)) {
 			if (backslash) {
 				backslash = 0;
 				if (c != '\n')
 					goto put;
 				continue;
 			}
 			if (c == '\\') {
 				backslash = 1;
 				continue;
 			}
 		}
 		if (c == delim) /* '\n' or -d CHAR */
 			break;
 		if (c == '\0')
 			continue;

 		/* $IFS splitting. NOT done if we run "read"
 		 * without variable names (bash compat).
 		 * Thus, "read" and "read REPLY" are not the same.
 		 */
 		if (argv[0]) {
 /* http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_05 */
 			const char *is_ifs = strchr(ifs, c);
 			if (startword && is_ifs) {
 				if (isspace(c))
 					continue;
 				/* it is a non-space ifs char */
 				startword--;
 				if (startword == 1) /* first one? */
 					continue; /* yes, it is not next word yet */
 			}
 			startword = 0;
 			if (argv[1] != NULL && is_ifs) {
 				buffer[bufpos] = '\0';
 				bufpos = 0;
 				params->setvar(*argv, buffer);
 				argv++;
 				/* can we skip one non-space ifs char? (2: yes) */
 				startword = isspace(c) ? 2 : 1;
 				continue;
 			}
 		}
  put:
 		bufpos++;
 	} while (--nchars);

 	if (argv[0]) {
 		/* Remove trailing space $IFS chars */
 		while (--bufpos >= 0
 		 && isspace(buffer[bufpos])
 		 && strchr(ifs, buffer[bufpos]) != NULL
 		) {
 			continue;
 		}
 		buffer[bufpos + 1] = '\0';

 		/* Last variable takes the entire remainder with delimiters
 		 * (sans trailing whitespace $IFS),
 		 * but ***only "if there are fewer vars than fields"(c)***!
 		 * The "X:Y:" case below: there are two fields,
 		 * and therefore last delimiter (:) is eaten:
 		 * IFS=": "
 		 * echo "X:Y:Z:"  | (read x y; echo "|$x|$y|") # |X|Y:Z:|
 		 * echo "X:Y:Z"   | (read x y; echo "|$x|$y|") # |X|Y:Z|
 		 * echo "X:Y:"    | (read x y; echo "|$x|$y|") # |X|Y|, not |X|Y:|
 		 * echo "X:Y  : " | (read x y; echo "|$x|$y|") # |X|Y|
 		 */
 		if (bufpos >= 0
 		 && strchr(ifs, buffer[bufpos]) != NULL
 		) {
 			/* There _is_ a non-whitespace IFS char */
 			/* Skip whitespace IFS char before it */
 			while (--bufpos >= 0
 			 && isspace(buffer[bufpos])
 			 && strchr(ifs, buffer[bufpos]) != NULL
 			) {
 				continue;
 			}
 			/* Are there $IFS chars? */
 			if (strcspn(buffer, ifs) >= ++bufpos) {
 				/* No: last var takes one field, not more */
 				/* So, drop trailing IFS delims */
 				buffer[bufpos] = '\0';
 			}
 		}

 		/* Use the remainder as a value for the next variable */
 		params->setvar(*argv, buffer);
 		/* Set the rest to "" */
 		while (*++argv)
 			params->setvar(*argv, "");
 	} else {
 		/* Note: no $IFS removal */
 		buffer[bufpos] = '\0';
 		params->setvar("REPLY", buffer);
 	}

  ret:
 	free(buffer);
 	if (read_flags & BUILTIN_READ_SILENT)
 		tcsetattr(fd, TCSANOW, &old_tty);

 	errno = err;
 	return retval;
 #undef fd
 }

 /* ulimit builtin */

 struct limits {
 	uint8_t cmd;            /* RLIMIT_xxx fit into it */
 	uint8_t factor_shift;   /* shift by to get rlim_{cur,max} values */
 };

 /* Order of entries matches order in which bash prints "ulimit -a" */
 static const struct limits limits_tbl[] ALIGN2 = {
 	{ RLIMIT_CORE,		9,	}, // -c
 	{ RLIMIT_DATA,		10,	}, // -d
 #ifdef RLIMIT_NICE
 	{ RLIMIT_NICE,		0,	}, // -e
 #define LIMIT_F_IDX     3
 #else
 /* for example, Hurd */
 #define LIMIT_F_IDX     2
 #endif
 	{ RLIMIT_FSIZE,		9,	}, // -f
 #ifdef RLIMIT_SIGPENDING
 	{ RLIMIT_SIGPENDING,	0,	}, // -i
 #endif
 #ifdef RLIMIT_MEMLOCK
 	{ RLIMIT_MEMLOCK,	10,	}, // -l
 #endif
 #ifdef RLIMIT_RSS
 	{ RLIMIT_RSS,		10,	}, // -m
 #endif
 #ifdef RLIMIT_NOFILE
 	{ RLIMIT_NOFILE,	0,	}, // -n
 #endif
 #ifdef RLIMIT_MSGQUEUE
 	{ RLIMIT_MSGQUEUE,	0,	}, // -q
 #endif
 #ifdef RLIMIT_RTPRIO
 	{ RLIMIT_RTPRIO,	0,	}, // -r
 #endif
 #ifdef RLIMIT_STACK
 	{ RLIMIT_STACK,		10,	}, // -s
 #endif
 #ifdef RLIMIT_CPU
 	{ RLIMIT_CPU,		0,	}, // -t
 #endif
 #ifdef RLIMIT_NPROC
 	{ RLIMIT_NPROC,		0,	}, // -u
 #endif
 #ifdef RLIMIT_AS
 	{ RLIMIT_AS,		10,	}, // -v
 #endif
 #ifdef RLIMIT_LOCKS
 	{ RLIMIT_LOCKS,		0,	}, // -x
 #endif
 };
 // 1) bash also shows:
 //pipe size            (512 bytes, -p) 8
 // 2) RLIMIT_RTTIME ("timeout for RT tasks in us") is not in the table

 static const char limits_help[] ALIGN1 =
 	"core file size (blocks)"          // -c
 	"\0""data seg size (kb)"           // -d
 #ifdef RLIMIT_NICE
 	"\0""scheduling priority"          // -e
 #endif
 	"\0""file size (blocks)"           // -f
 #ifdef RLIMIT_SIGPENDING
 	"\0""pending signals"              // -i
 #endif
 #ifdef RLIMIT_MEMLOCK
 	"\0""max locked memory (kb)"       // -l
 #endif
 #ifdef RLIMIT_RSS
 	"\0""max memory size (kb)"         // -m
 #endif
 #ifdef RLIMIT_NOFILE
 	"\0""open files"                   // -n
 #endif
 #ifdef RLIMIT_MSGQUEUE
 	"\0""POSIX message queues (bytes)" // -q
 #endif
 #ifdef RLIMIT_RTPRIO
 	"\0""real-time priority"           // -r
 #endif
 #ifdef RLIMIT_STACK
 	"\0""stack size (kb)"              // -s
 #endif
 #ifdef RLIMIT_CPU
 	"\0""cpu time (seconds)"           // -t
 #endif
 #ifdef RLIMIT_NPROC
 	"\0""max user processes"           // -u
 #endif
 #ifdef RLIMIT_AS
 	"\0""virtual memory (kb)"          // -v
 #endif
 #ifdef RLIMIT_LOCKS
 	"\0""file locks"                   // -x
 #endif
 ;

 static const char limit_chars[] ALIGN1 =
 			"c"
 			"d"
 #ifdef RLIMIT_NICE
 			"e"
 #endif
 			"f"
 #ifdef RLIMIT_SIGPENDING
 			"i"
 #endif
 #ifdef RLIMIT_MEMLOCK
 			"l"
 #endif
 #ifdef RLIMIT_RSS
 			"m"
 #endif
 #ifdef RLIMIT_NOFILE
 			"n"
 #endif
 #ifdef RLIMIT_MSGQUEUE
 			"q"
 #endif
 #ifdef RLIMIT_RTPRIO
 			"r"
 #endif
 #ifdef RLIMIT_STACK
 			"s"
 #endif
 #ifdef RLIMIT_CPU
 			"t"
 #endif
 #ifdef RLIMIT_NPROC
 			"u"
 #endif
 #ifdef RLIMIT_AS
 			"v"
 #endif
 #ifdef RLIMIT_LOCKS
 			"x"
 #endif
 ;

 /* "-": treat args as parameters of option with ASCII code 1 */
 static const char ulimit_opt_string[] ALIGN1 = "-HSa"
 			"c::"
 			"d::"
 #ifdef RLIMIT_NICE
 			"e::"
 #endif
 			"f::"
 #ifdef RLIMIT_SIGPENDING
 			"i::"
 #endif
 #ifdef RLIMIT_MEMLOCK
 			"l::"
 #endif
 #ifdef RLIMIT_RSS
 			"m::"
 #endif
 #ifdef RLIMIT_NOFILE
 			"n::"
 #endif
 #ifdef RLIMIT_MSGQUEUE
 			"q::"
 #endif
 #ifdef RLIMIT_RTPRIO
 			"r::"
 #endif
 #ifdef RLIMIT_STACK
 			"s::"
 #endif
 #ifdef RLIMIT_CPU
 			"t::"
 #endif
 #ifdef RLIMIT_NPROC
 			"u::"
 #endif
 #ifdef RLIMIT_AS
 			"v::"
 #endif
 #ifdef RLIMIT_LOCKS
 			"x::"
 #endif
 ;

 enum {
 	OPT_hard = (1 << 0),
 	OPT_soft = (1 << 1),
 	OPT_all  = (1 << 2),
 };

 static void printlim(unsigned opts, const struct rlimit *limit,
 			const struct limits *l)
 {
 	rlim_t val;

 	val = limit->rlim_max;
 	if (opts & OPT_soft)
 		val = limit->rlim_cur;

 	if (val == RLIM_INFINITY)
 		puts("unlimited");
 	else {
 		val >>= l->factor_shift;
 		printf("%llu\n", (long long) val);
 	}
 }

 int FAST_FUNC
 shell_builtin_ulimit(char **argv)
 {
 	struct rlimit limit;
 	unsigned opt_cnt;
 	unsigned opts;
 	unsigned argc;
 	unsigned i;

 	/* We can't use getopt32: need to handle commands like
 	 * ulimit 123 -c2 -l 456
 	 */

 	/* In case getopt() was already called:
 	 * reset libc getopt() internal state.
 	 */
 	GETOPT_RESET();

 // bash 4.4.23:
 //
 // -H and/or -S change meaning even of options *before* them: ulimit -f 2000 -H
 // sets hard limit, ulimit -a -H prints hard limits.
 //
 // -a is equivalent for requesting all limits to be shown.
 //
 // If -a is specified, attempts to set limits are ignored:
 //  ulimit -m 1000; ulimit -m 2000 -a
 // shows 1000, not 2000. HOWEVER, *implicit* -f form "ulimit 2000 -a"
 // DOES set -f limit [we don't implement this quirk], "ulimit -a 2000" does not.
 // Options are still parsed: ulimit -az complains about unknown -z opt.
 //
 // -a is not cumulative: "ulimit -a -a" = "ulimit -a -f -m" = "ulimit -a"
 //
 // -HSa can be combined in one argument and with one other option (example: -Sm),
 // but other options can't: limit value is an optional argument,
 // thus "-mf" means "-m f", f is the parameter of -m.
 //
 // Limit can be set and then printed: ulimit -m 2000 -m
 // If set more than once, they are set and printed in order:
 // try ulimit -m -m 1000 -m -m 2000 -m -m 3000 -m
 //
 // Limits are shown in the order of options given:
 // ulimit -m -f is not the same as ulimit -f -m.
 //
 // If both -S and -H are given, show soft limit.
 //
 // Short printout (limit value only) is printed only if just one option
 // is given: ulimit -m. ulimit -f -m prints verbose lines.
 // ulimit -f -f prints same verbose line twice.
 // ulimit -m 10000 -f prints verbose line for -f.

 	argc = string_array_len(argv);

 	/* First pass over options: detect -H/-S/-a status,
 	 * and "bare ulimit" and "only one option" cases
 	 * by counting other opts.
 	 */
 	opt_cnt = 0;
 	opts = 0;
 	while (1) {
 		int opt_char = getopt(argc, argv, ulimit_opt_string);

 		if (opt_char == -1)
 			break;
 		if (opt_char == 'H') {
 			opts |= OPT_hard;
 			continue;
 		}
 		if (opt_char == 'S') {
 			opts |= OPT_soft;
 			continue;
 		}
 		if (opt_char == 'a') {
 			opts |= OPT_all;
 			continue;
 		}
 		if (opt_char == '?') {
 			/* bad option. getopt already complained. */
 			return EXIT_FAILURE;
 		}
 		opt_cnt++;
 	} /* while (there are options) */

 	if (!(opts & (OPT_hard | OPT_soft)))
 		opts |= (OPT_hard | OPT_soft);
 	if (opts & OPT_all) {
 		const char *help = limits_help;
 		for (i = 0; i < ARRAY_SIZE(limits_tbl); i++) {
 			getrlimit(limits_tbl[i].cmd, &limit);
 			printf("%-32s(-%c) ", help, limit_chars[i]);
 			printlim(opts, &limit, &limits_tbl[i]);
 			help += strlen(help) + 1;
 		}
 		return EXIT_SUCCESS;
 	}

 	/* Second pass: set or print limits, in order */
 	GETOPT_RESET();
 	while (1) {
 		char *val_str;
 		int opt_char = getopt(argc, argv, ulimit_opt_string);

 		if (opt_char == -1)
 			break;
 		if (opt_char == 'H')
 			continue;
 		if (opt_char == 'S')
 			continue;
 		//if (opt_char == 'a') - impossible

 		if (opt_char == 1) /* if "ulimit NNN", -f is assumed */
 			opt_char = 'f';
 		i = strchrnul(limit_chars, opt_char) - limit_chars;
 		//if (i >= ARRAY_SIZE(limits_tbl)) - bad option, impossible

 		val_str = optarg;
 		if (!val_str && argv[optind] && argv[optind][0] != '-')
 			val_str = argv[optind++]; /* ++ skips NN in "-c NN" case */

 		getrlimit(limits_tbl[i].cmd, &limit);
 		if (!val_str) {
 			if (opt_cnt > 1)
 				printf("%-32s(-%c) ", nth_string(limits_help, i), limit_chars[i]);
 			printlim(opts, &limit, &limits_tbl[i]);
 		} else {
 			rlim_t val = RLIM_INFINITY;
 			if (strcmp(val_str, "unlimited") != 0) {
 				if (sizeof(val) == sizeof(int))
 					val = bb_strtou(val_str, NULL, 10);
 				else if (sizeof(val) == sizeof(long))
 					val = bb_strtoul(val_str, NULL, 10);
 				else
 					val = bb_strtoull(val_str, NULL, 10);
 				if (errno) {
 					bb_error_msg("invalid number '%s'", val_str);
 					return EXIT_FAILURE;
 				}
 				val <<= limits_tbl[i].factor_shift;
 			}
 //bb_error_msg("opt %c val_str:'%s' val:%lld", opt_char, val_str, (long long)val);
 			/* from man bash: "If neither -H nor -S
 			 * is specified, both the soft and hard
 			 * limits are set. */
 			if (opts & OPT_hard)
 				limit.rlim_max = val;
 			if (opts & OPT_soft)
 				limit.rlim_cur = val;
 //bb_error_msg("setrlimit(%d, %lld, %lld)", limits_tbl[i].cmd, (long long)limit.rlim_cur, (long long)limit.rlim_max);
 			if (setrlimit(limits_tbl[i].cmd, &limit) < 0) {
 				bb_simple_perror_msg("error setting limit");
 				return EXIT_FAILURE;
 			}
 		}
 	} /* while (there are options) */

 	if (opt_cnt == 0) {
 		/* "bare ulimit": treat it as if it was -f */
 		getrlimit(RLIMIT_FSIZE, &limit);
 		printlim(opts, &limit, &limits_tbl[LIMIT_F_IDX]);
 	}

 	return EXIT_SUCCESS;
 }
	/* vi: set sw=4 ts=4: */
	/*
	* Adapted from ash applet code
	*
	* This code is derived from software contributed to Berkeley by
	* Kenneth Almquist.
	*
	* Copyright (c) 1989, 1991, 1993, 1994
	* The Regents of the University of California. All rights reserved.
	*
	* Copyright (c) 1997-2005 Herbert Xu <herbert@gondor.apana.org.au>
	* was re-ported from NetBSD and debianized.
	*
	* Copyright (c) 2010 Denys Vlasenko
	* Split from ash.c
	*
	* Licensed under GPLv2 or later, see file LICENSE in this source tree.
	*/
	#include "libbb.h"
	#include "shell_common.h"

	const char defifsvar[] ALIGN1 = "IFS= \t\n";
	const char defoptindvar[] ALIGN1 = "OPTIND=1";

	/* read builtin */

	/* Needs to be interruptible: shell must handle traps and shell-special signals
	* while inside read. To implement this, be sure to not loop on EINTR
	* and return errno == EINTR reliably.
	*/
	//TODO: use more efficient setvar() which takes a pointer to malloced "VAR=VAL"
	//string. hush naturally has it, and ash has setvareq().
	//Here we can simply store "VAR=" at buffer start and store read data directly
	//after "=", then pass buffer to setvar() to consume.
	const char* FAST_FUNC
	shell_builtin_read(struct builtin_read_params *params)
	{
	struct pollfd pfd[1];
	#define fd (pfd[0].fd) /* -u FD */
	unsigned err;
	unsigned end_ms; /* -t TIMEOUT */
	int nchars; /* -n NUM */
	char **pp;
	char *buffer;
	char delim;
	struct termios tty, old_tty;
	const char *retval;
	int bufpos; /* need to be able to hold -1 */
	int startword;
	smallint backslash;
	char **argv;
	const char *ifs;
	int read_flags;

	errno = err = 0;

	argv = params->argv;
	pp = argv;
	while (*pp) {
	if (endofname(*pp)[0] != '\0') {
	/* Mimic bash message */
	bb_error_msg("read: '%s': bad variable name", *pp);
	return (const char *)(uintptr_t)1;
	}
	pp++;
	}

	nchars = 0; /* if != 0, -n is in effect */
	if (params->opt_n) {
	nchars = bb_strtou(params->opt_n, NULL, 10);
	if (nchars < 0 \|\| errno)
	return "invalid count";
	/* note: "-n 0": off (bash 3.2 does this too) */
	}

	end_ms = 0;
	if (params->opt_t && !ENABLE_FEATURE_SH_READ_FRAC) {
	end_ms = bb_strtou(params->opt_t, NULL, 10);
	if (errno)
	return "invalid timeout";
	if (end_ms > UINT_MAX / 2048) /* be safely away from overflow */
	end_ms = UINT_MAX / 2048;
	end_ms *= 1000;
	}
	if (params->opt_t && ENABLE_FEATURE_SH_READ_FRAC) {
	/* bash 4.3 (maybe earlier) supports -t N.NNNNNN */
	char *p;
	/* Eat up to three fractional digits */
	int frac_digits = 3 + 1;

	end_ms = bb_strtou(params->opt_t, &p, 10);
	if (end_ms > UINT_MAX / 2048) /* be safely away from overflow */
	end_ms = UINT_MAX / 2048;

	if (errno) {
	/* EINVAL = number is ok, but not NUL terminated */
	if (errno != EINVAL \|\| *p != '.')
	return "invalid timeout";
	/* Do not check the rest: bash allows "0.123456xyz" */
	while (*++p && --frac_digits) {
	end_ms *= 10;
	end_ms += (*p - '0');
	if ((unsigned char)(*p - '0') > 9)
	return "invalid timeout";
	}
	}
	while (--frac_digits > 0) {
	end_ms *= 10;
	}
	}

	fd = STDIN_FILENO;
	if (params->opt_u) {
	fd = bb_strtou(params->opt_u, NULL, 10);
	if (fd < 0 \|\| errno)
	return "invalid file descriptor";
	}

	if (params->opt_t && end_ms == 0) {
	/* "If timeout is 0, read returns immediately, without trying
	* to read any data. The exit status is 0 if input is available
	* on the specified file descriptor, non-zero otherwise."
	* bash seems to ignore -p PROMPT for this use case.
	*/
	int r;
	pfd[0].events = POLLIN;
	r = poll(pfd, 1, /timeout:/ 0);
	/* Return 0 only if poll returns 1 ("one fd ready"), else return 1: */
	return (const char *)(uintptr_t)(r <= 0);
	}

	if (params->opt_p && isatty(fd)) {
	fputs(params->opt_p, stderr);
	fflush_all();
	}

	ifs = params->ifs;
	if (ifs == NULL)
	ifs = defifs;

	read_flags = params->read_flags;
	if (nchars \|\| (read_flags & BUILTIN_READ_SILENT)) {
	tcgetattr(fd, &tty);
	old_tty = tty;
	if (nchars) {
	tty.c_lflag &= ~ICANON;
	// Setting it to more than 1 breaks poll():
	// it blocks even if there's data. !??
	//tty.c_cc[VMIN] = nchars < 256 ? nchars : 255;
	/* reads will block only if < 1 char is available */
	tty.c_cc[VMIN] = 1;
	/* no timeout (reads block forever) */
	tty.c_cc[VTIME] = 0;
	}
	if (read_flags & BUILTIN_READ_SILENT) {
	tty.c_lflag &= ~(ECHO \| ECHOK \| ECHONL);
	}
	/* This forces execution of "restoring" tcgetattr later */
	read_flags \|= BUILTIN_READ_SILENT;
	/* if tcgetattr failed, tcsetattr will fail too.
	* Ignoring, it's harmless. */
	tcsetattr(fd, TCSANOW, &tty);
	}

	retval = (const char *)(uintptr_t)0;
	startword = 1;
	backslash = 0;
	if (params->opt_t)
	end_ms += (unsigned)monotonic_ms();
	buffer = NULL;
	bufpos = 0;
	delim = params->opt_d ? params->opt_d[0] : '\n';
	do {
	char c;
	int timeout;

	if ((bufpos & 0xff) == 0)
	buffer = xrealloc(buffer, bufpos + 0x101);

	timeout = -1;
	if (params->opt_t) {
	timeout = end_ms - (unsigned)monotonic_ms();
	/* ^^^^^^^^^^^^^ all values are unsigned,
	* wrapping math is used here, good even if
	* 32-bit unix time wrapped (year 2038+).
	*/
	if (timeout <= 0) { /* already late? */
	retval = (const char *)(uintptr_t)1;
	goto ret;
	}
	}

	/* We must poll even if timeout is -1:
	* we want to be interrupted if signal arrives,
	* regardless of SA_RESTART-ness of that signal!
	*/
	errno = 0;
	pfd[0].events = POLLIN;
	//TODO race with a signal arriving just before the poll!
	if (poll(pfd, 1, timeout) <= 0) {
	/* timed out, or EINTR */
	err = errno;
	retval = (const char *)(uintptr_t)1;
	goto ret;
	}
	if (read(fd, &buffer[bufpos], 1) != 1) {
	err = errno;
	retval = (const char *)(uintptr_t)1;
	break;
	}

	c = buffer[bufpos];
	if (!(read_flags & BUILTIN_READ_RAW)) {
	if (backslash) {
	backslash = 0;
	if (c != '\n')
	goto put;
	continue;
	}
	if (c == '\\') {
	backslash = 1;
	continue;
	}
	}
	if (c == delim) /* '\n' or -d CHAR */
	break;
	if (c == '\0')
	continue;

	/* $IFS splitting. NOT done if we run "read"
	* without variable names (bash compat).
	* Thus, "read" and "read REPLY" are not the same.
	*/
	if (argv[0]) {
	/* http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_05 */
	const char *is_ifs = strchr(ifs, c);
	if (startword && is_ifs) {
	if (isspace(c))
	continue;
	/* it is a non-space ifs char */
	startword--;
	if (startword == 1) /* first one? */
	continue; /* yes, it is not next word yet */
	}
	startword = 0;
	if (argv[1] != NULL && is_ifs) {
	buffer[bufpos] = '\0';
	bufpos = 0;
	params->setvar(*argv, buffer);
	argv++;
	/* can we skip one non-space ifs char? (2: yes) */
	startword = isspace(c) ? 2 : 1;
	continue;
	}
	}
	put:
	bufpos++;
	} while (--nchars);

	if (argv[0]) {
	/* Remove trailing space $IFS chars */
	while (--bufpos >= 0
	&& isspace(buffer[bufpos])
	&& strchr(ifs, buffer[bufpos]) != NULL
	) {
	continue;
	}
	buffer[bufpos + 1] = '\0';

	/* Last variable takes the entire remainder with delimiters
	* (sans trailing whitespace $IFS),
	* but *only "if there are fewer vars than fields"(c)*!
	* The "X:Y:" case below: there are two fields,
	* and therefore last delimiter (:) is eaten:
	* IFS=": "
	* echo "X:Y:Z:" \| (read x y; echo "\|$x\|$y\|") # \|X\|Y:Z:\|
	* echo "X:Y:Z" \| (read x y; echo "\|$x\|$y\|") # \|X\|Y:Z\|
	* echo "X:Y:" \| (read x y; echo "\|$x\|$y\|") # \|X\|Y\|, not \|X\|Y:\|
	* echo "X:Y : " \| (read x y; echo "\|$x\|$y\|") # \|X\|Y\|
	*/
	if (bufpos >= 0
	&& strchr(ifs, buffer[bufpos]) != NULL
	) {
	/* There _is_ a non-whitespace IFS char */
	/* Skip whitespace IFS char before it */
	while (--bufpos >= 0
	&& isspace(buffer[bufpos])
	&& strchr(ifs, buffer[bufpos]) != NULL
	) {
	continue;
	}
	/* Are there $IFS chars? */
	if (strcspn(buffer, ifs) >= ++bufpos) {
	/* No: last var takes one field, not more */
	/* So, drop trailing IFS delims */
	buffer[bufpos] = '\0';
	}
	}

	/* Use the remainder as a value for the next variable */
	params->setvar(*argv, buffer);
	/* Set the rest to "" */
	while (*++argv)
	params->setvar(*argv, "");
	} else {
	/* Note: no $IFS removal */
	buffer[bufpos] = '\0';
	params->setvar("REPLY", buffer);
	}

	ret:
	free(buffer);
	if (read_flags & BUILTIN_READ_SILENT)
	tcsetattr(fd, TCSANOW, &old_tty);

	errno = err;
	return retval;
	#undef fd
	}

	/* ulimit builtin */

	struct limits {
	uint8_t cmd; /* RLIMIT_xxx fit into it */
	uint8_t factor_shift; /* shift by to get rlim_{cur,max} values */
	};

	/* Order of entries matches order in which bash prints "ulimit -a" */
	static const struct limits limits_tbl[] ALIGN2 = {
	{ RLIMIT_CORE, 9, }, // -c
	{ RLIMIT_DATA, 10, }, // -d
	#ifdef RLIMIT_NICE
	{ RLIMIT_NICE, 0, }, // -e
	#define LIMIT_F_IDX 3
	#else
	/* for example, Hurd */
	#define LIMIT_F_IDX 2
	#endif
	{ RLIMIT_FSIZE, 9, }, // -f
	#ifdef RLIMIT_SIGPENDING
	{ RLIMIT_SIGPENDING, 0, }, // -i
	#endif
	#ifdef RLIMIT_MEMLOCK
	{ RLIMIT_MEMLOCK, 10, }, // -l
	#endif
	#ifdef RLIMIT_RSS
	{ RLIMIT_RSS, 10, }, // -m
	#endif
	#ifdef RLIMIT_NOFILE
	{ RLIMIT_NOFILE, 0, }, // -n
	#endif
	#ifdef RLIMIT_MSGQUEUE
	{ RLIMIT_MSGQUEUE, 0, }, // -q
	#endif
	#ifdef RLIMIT_RTPRIO
	{ RLIMIT_RTPRIO, 0, }, // -r
	#endif
	#ifdef RLIMIT_STACK
	{ RLIMIT_STACK, 10, }, // -s
	#endif
	#ifdef RLIMIT_CPU
	{ RLIMIT_CPU, 0, }, // -t
	#endif
	#ifdef RLIMIT_NPROC
	{ RLIMIT_NPROC, 0, }, // -u
	#endif
	#ifdef RLIMIT_AS
	{ RLIMIT_AS, 10, }, // -v
	#endif
	#ifdef RLIMIT_LOCKS
	{ RLIMIT_LOCKS, 0, }, // -x
	#endif
	};
	// 1) bash also shows:
	//pipe size (512 bytes, -p) 8
	// 2) RLIMIT_RTTIME ("timeout for RT tasks in us") is not in the table

	static const char limits_help[] ALIGN1 =
	"core file size (blocks)" // -c
	"\0""data seg size (kb)" // -d
	#ifdef RLIMIT_NICE
	"\0""scheduling priority" // -e
	#endif
	"\0""file size (blocks)" // -f
	#ifdef RLIMIT_SIGPENDING
	"\0""pending signals" // -i
	#endif
	#ifdef RLIMIT_MEMLOCK
	"\0""max locked memory (kb)" // -l
	#endif
	#ifdef RLIMIT_RSS
	"\0""max memory size (kb)" // -m
	#endif
	#ifdef RLIMIT_NOFILE
	"\0""open files" // -n
	#endif
	#ifdef RLIMIT_MSGQUEUE
	"\0""POSIX message queues (bytes)" // -q
	#endif
	#ifdef RLIMIT_RTPRIO
	"\0""real-time priority" // -r
	#endif
	#ifdef RLIMIT_STACK
	"\0""stack size (kb)" // -s
	#endif
	#ifdef RLIMIT_CPU
	"\0""cpu time (seconds)" // -t
	#endif
	#ifdef RLIMIT_NPROC
	"\0""max user processes" // -u
	#endif
	#ifdef RLIMIT_AS
	"\0""virtual memory (kb)" // -v
	#endif
	#ifdef RLIMIT_LOCKS
	"\0""file locks" // -x
	#endif
	;

	static const char limit_chars[] ALIGN1 =
	"c"
	"d"
	#ifdef RLIMIT_NICE
	"e"
	#endif
	"f"
	#ifdef RLIMIT_SIGPENDING
	"i"
	#endif
	#ifdef RLIMIT_MEMLOCK
	"l"
	#endif
	#ifdef RLIMIT_RSS
	"m"
	#endif
	#ifdef RLIMIT_NOFILE
	"n"
	#endif
	#ifdef RLIMIT_MSGQUEUE
	"q"
	#endif
	#ifdef RLIMIT_RTPRIO
	"r"
	#endif
	#ifdef RLIMIT_STACK
	"s"
	#endif
	#ifdef RLIMIT_CPU
	"t"
	#endif
	#ifdef RLIMIT_NPROC
	"u"
	#endif
	#ifdef RLIMIT_AS
	"v"
	#endif
	#ifdef RLIMIT_LOCKS
	"x"
	#endif
	;

	/* "-": treat args as parameters of option with ASCII code 1 */
	static const char ulimit_opt_string[] ALIGN1 = "-HSa"
	"c::"
	"d::"
	#ifdef RLIMIT_NICE
	"e::"
	#endif
	"f::"
	#ifdef RLIMIT_SIGPENDING
	"i::"
	#endif
	#ifdef RLIMIT_MEMLOCK
	"l::"
	#endif
	#ifdef RLIMIT_RSS
	"m::"
	#endif
	#ifdef RLIMIT_NOFILE
	"n::"
	#endif
	#ifdef RLIMIT_MSGQUEUE
	"q::"
	#endif
	#ifdef RLIMIT_RTPRIO
	"r::"
	#endif
	#ifdef RLIMIT_STACK
	"s::"
	#endif
	#ifdef RLIMIT_CPU
	"t::"
	#endif
	#ifdef RLIMIT_NPROC
	"u::"
	#endif
	#ifdef RLIMIT_AS
	"v::"
	#endif
	#ifdef RLIMIT_LOCKS
	"x::"
	#endif
	;

	enum {
	OPT_hard = (1 << 0),
	OPT_soft = (1 << 1),
	OPT_all = (1 << 2),
	};

	static void printlim(unsigned opts, const struct rlimit *limit,
	const struct limits *l)
	{
	rlim_t val;

	val = limit->rlim_max;
	if (opts & OPT_soft)
	val = limit->rlim_cur;

	if (val == RLIM_INFINITY)
	puts("unlimited");
	else {
	val >>= l->factor_shift;
	printf("%llu\n", (long long) val);
	}
	}

	int FAST_FUNC
	shell_builtin_ulimit(char **argv)
	{
	struct rlimit limit;
	unsigned opt_cnt;
	unsigned opts;
	unsigned argc;
	unsigned i;

	/* We can't use getopt32: need to handle commands like
	* ulimit 123 -c2 -l 456
	*/

	/* In case getopt() was already called:
	* reset libc getopt() internal state.
	*/
	GETOPT_RESET();

	// bash 4.4.23:
	//
	// -H and/or -S change meaning even of options before them: ulimit -f 2000 -H
	// sets hard limit, ulimit -a -H prints hard limits.
	//
	// -a is equivalent for requesting all limits to be shown.
	//
	// If -a is specified, attempts to set limits are ignored:
	// ulimit -m 1000; ulimit -m 2000 -a
	// shows 1000, not 2000. HOWEVER, implicit -f form "ulimit 2000 -a"
	// DOES set -f limit [we don't implement this quirk], "ulimit -a 2000" does not.
	// Options are still parsed: ulimit -az complains about unknown -z opt.
	//
	// -a is not cumulative: "ulimit -a -a" = "ulimit -a -f -m" = "ulimit -a"
	//
	// -HSa can be combined in one argument and with one other option (example: -Sm),
	// but other options can't: limit value is an optional argument,
	// thus "-mf" means "-m f", f is the parameter of -m.
	//
	// Limit can be set and then printed: ulimit -m 2000 -m
	// If set more than once, they are set and printed in order:
	// try ulimit -m -m 1000 -m -m 2000 -m -m 3000 -m
	//
	// Limits are shown in the order of options given:
	// ulimit -m -f is not the same as ulimit -f -m.
	//
	// If both -S and -H are given, show soft limit.
	//
	// Short printout (limit value only) is printed only if just one option
	// is given: ulimit -m. ulimit -f -m prints verbose lines.
	// ulimit -f -f prints same verbose line twice.
	// ulimit -m 10000 -f prints verbose line for -f.

	argc = string_array_len(argv);

	/* First pass over options: detect -H/-S/-a status,
	* and "bare ulimit" and "only one option" cases
	* by counting other opts.
	*/
	opt_cnt = 0;
	opts = 0;
	while (1) {
	int opt_char = getopt(argc, argv, ulimit_opt_string);

	if (opt_char == -1)
	break;
	if (opt_char == 'H') {
	opts \|= OPT_hard;
	continue;
	}
	if (opt_char == 'S') {
	opts \|= OPT_soft;
	continue;
	}
	if (opt_char == 'a') {
	opts \|= OPT_all;
	continue;
	}
	if (opt_char == '?') {
	/* bad option. getopt already complained. */
	return EXIT_FAILURE;
	}
	opt_cnt++;
	} /* while (there are options) */

	if (!(opts & (OPT_hard \| OPT_soft)))
	opts \|= (OPT_hard \| OPT_soft);
	if (opts & OPT_all) {
	const char *help = limits_help;
	for (i = 0; i < ARRAY_SIZE(limits_tbl); i++) {
	getrlimit(limits_tbl[i].cmd, &limit);
	printf("%-32s(-%c) ", help, limit_chars[i]);
	printlim(opts, &limit, &limits_tbl[i]);
	help += strlen(help) + 1;
	}
	return EXIT_SUCCESS;
	}

	/* Second pass: set or print limits, in order */
	GETOPT_RESET();
	while (1) {
	char *val_str;
	int opt_char = getopt(argc, argv, ulimit_opt_string);

	if (opt_char == -1)
	break;
	if (opt_char == 'H')
	continue;
	if (opt_char == 'S')
	continue;
	//if (opt_char == 'a') - impossible

	if (opt_char == 1) /* if "ulimit NNN", -f is assumed */
	opt_char = 'f';
	i = strchrnul(limit_chars, opt_char) - limit_chars;
	//if (i >= ARRAY_SIZE(limits_tbl)) - bad option, impossible

	val_str = optarg;
	if (!val_str && argv[optind] && argv[optind][0] != '-')
	val_str = argv[optind++]; /* ++ skips NN in "-c NN" case */

	getrlimit(limits_tbl[i].cmd, &limit);
	if (!val_str) {
	if (opt_cnt > 1)
	printf("%-32s(-%c) ", nth_string(limits_help, i), limit_chars[i]);
	printlim(opts, &limit, &limits_tbl[i]);
	} else {
	rlim_t val = RLIM_INFINITY;
	if (strcmp(val_str, "unlimited") != 0) {
	if (sizeof(val) == sizeof(int))
	val = bb_strtou(val_str, NULL, 10);
	else if (sizeof(val) == sizeof(long))
	val = bb_strtoul(val_str, NULL, 10);
	else
	val = bb_strtoull(val_str, NULL, 10);
	if (errno) {
	bb_error_msg("invalid number '%s'", val_str);
	return EXIT_FAILURE;
	}
	val <<= limits_tbl[i].factor_shift;
	}
	//bb_error_msg("opt %c val_str:'%s' val:%lld", opt_char, val_str, (long long)val);
	/* from man bash: "If neither -H nor -S
	* is specified, both the soft and hard
	* limits are set. */
	if (opts & OPT_hard)
	limit.rlim_max = val;
	if (opts & OPT_soft)
	limit.rlim_cur = val;
	//bb_error_msg("setrlimit(%d, %lld, %lld)", limits_tbl[i].cmd, (long long)limit.rlim_cur, (long long)limit.rlim_max);
	if (setrlimit(limits_tbl[i].cmd, &limit) < 0) {
	bb_simple_perror_msg("error setting limit");
	return EXIT_FAILURE;
	}
	}
	} /* while (there are options) */

	if (opt_cnt == 0) {
	/* "bare ulimit": treat it as if it was -f */
	getrlimit(RLIMIT_FSIZE, &limit);
	printlim(opts, &limit, &limits_tbl[LIMIT_F_IDX]);
	}

	return EXIT_SUCCESS;
	}