shell/hush.c

/* vi: set sw=4 ts=4: */
/*
 * A prototype Bourne shell grammar parser.
 * Intended to follow the original Thompson and Ritchie
 * "small and simple is beautiful" philosophy, which
 * incidentally is a good match to today's BusyBox.
 *
 * Copyright (C) 2000,2001  Larry Doolittle <larry@doolittle.boa.org>
 * Copyright (C) 2008,2009  Denys Vlasenko <vda.linux@googlemail.com>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 *
 * Credits:
 *      The parser routines proper are all original material, first
 *      written Dec 2000 and Jan 2001 by Larry Doolittle.  The
 *      execution engine, the builtins, and much of the underlying
 *      support has been adapted from busybox-0.49pre's lash, which is
 *      Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 *      written by Erik Andersen <andersen@codepoet.org>.  That, in turn,
 *      is based in part on ladsh.c, by Michael K. Johnson and Erik W.
 *      Troan, which they placed in the public domain.  I don't know
 *      how much of the Johnson/Troan code has survived the repeated
 *      rewrites.
 *
 * Other credits:
 *      o_addchr derived from similar w_addchar function in glibc-2.2.
 *      parse_redirect, redirect_opt_num, and big chunks of main
 *      and many builtins derived from contributions by Erik Andersen.
 *      Miscellaneous bugfixes from Matt Kraai.
 *
 * There are two big (and related) architecture differences between
 * this parser and the lash parser.  One is that this version is
 * actually designed from the ground up to understand nearly all
 * of the Bourne grammar.  The second, consequential change is that
 * the parser and input reader have been turned inside out.  Now,
 * the parser is in control, and asks for input as needed.  The old
 * way had the input reader in control, and it asked for parsing to
 * take place as needed.  The new way makes it much easier to properly
 * handle the recursion implicit in the various substitutions, especially
 * across continuation lines.
 *
 * TODOs:
 *      grep for "TODO" and fix (some of them are easy)
 *      make complex ${var%...} constructs support optional
 *      make here documents optional
 *      special variables (done: PWD, PPID, RANDOM)
 *      follow IFS rules more precisely, including update semantics
 *      tilde expansion
 *      aliases
 *      "command" missing features:
 *          command -p CMD: run CMD using default $PATH
 *              (can use this to override standalone shell as well?)
 *          command BLTIN: disables special-ness (e.g. errors do not abort)
 *          command -V CMD1 CMD2 CMD3 (multiple args) (not in standard)
 *      builtins mandated by standards we don't support:
 *          [un]alias, fc:
 *          fc -l[nr] [BEG] [END]: list range of commands in history
 *          fc [-e EDITOR] [BEG] [END]: edit/rerun range of commands
 *          fc -s [PAT=REP] [CMD]: rerun CMD, replacing PAT with REP
 *
 * Bash compat TODO:
 *      redirection of stdout+stderr: &> and >&
 *      reserved words: function select
 *      advanced test: [[ ]]
 *      process substitution: <(list) and >(list)
 *      =~: regex operator
 *      let EXPR [EXPR...]
 *          Each EXPR is an arithmetic expression (ARITHMETIC EVALUATION)
 *          If the last arg evaluates to 0, let returns 1; 0 otherwise.
 *          NB: let `echo 'a=a + 1'` - error (IOW: multi-word expansion is used)
 *      ((EXPR))
 *          The EXPR is evaluated according to ARITHMETIC EVALUATION.
 *          This is exactly equivalent to let "EXPR".
 *      $[EXPR]: synonym for $((EXPR))
 *      indirect expansion: ${!VAR}
 *      substring op on @: ${@:n:m}
 *
 * Won't do:
 *      Some builtins mandated by standards:
 *          newgrp [GRP]: not a builtin in bash but a suid binary
 *              which spawns a new shell with new group ID
 *
 * Status of [[ support:
 * [[ args ]] are CMD_SINGLEWORD_NOGLOB:
 *   v='a b'; [[ $v = 'a b' ]]; echo 0:$?
 *   [[ /bin/n* ]]; echo 0:$?
 * TODO:
 * &&/|| are AND/OR ops, -a/-o are not
 * quoting needs to be considered (-f is an operator, "-f" and ""-f are not; etc)
 * = is glob match operator, not equality operator: STR = GLOB
 * (in GLOB, quoting is significant on char-by-char basis: a*cd"*")
 * == same as =
 * add =~ regex match operator: STR =~ REGEX
 */
//config:config HUSH
//config:	bool "hush (68 kb)"
//config:	default y
//config:	help
//config:	hush is a small shell. It handles the normal flow control
//config:	constructs such as if/then/elif/else/fi, for/in/do/done, while loops,
//config:	case/esac. Redirections, here documents, $((arithmetic))
//config:	and functions are supported.
//config:
//config:	It will compile and work on no-mmu systems.
//config:
//config:	It does not handle select, aliases, tilde expansion,
//config:	&>file and >&file redirection of stdout+stderr.
//config:
//config:config HUSH_BASH_COMPAT
//config:	bool "bash-compatible extensions"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_BRACE_EXPANSION
//config:	bool "Brace expansion"
//config:	default y
//config:	depends on HUSH_BASH_COMPAT
//config:	help
//config:	Enable {abc,def} extension.
//config:
//config:config HUSH_LINENO_VAR
//config:	bool "$LINENO variable"
//config:	default y
//config:	depends on HUSH_BASH_COMPAT
//config:
//config:config HUSH_BASH_SOURCE_CURDIR
//config:	bool "'source' and '.' builtins search current directory after $PATH"
//config:	default n   # do not encourage non-standard behavior
//config:	depends on HUSH_BASH_COMPAT
//config:	help
//config:	This is not compliant with standards. Avoid if possible.
//config:
//config:config HUSH_INTERACTIVE
//config:	bool "Interactive mode"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	Enable interactive mode (prompt and command editing).
//config:	Without this, hush simply reads and executes commands
//config:	from stdin just like a shell script from a file.
//config:	No prompt, no PS1/PS2 magic shell variables.
//config:
//config:config HUSH_SAVEHISTORY
//config:	bool "Save command history to .hush_history"
//config:	default y
//config:	depends on HUSH_INTERACTIVE && FEATURE_EDITING_SAVEHISTORY
//config:
//config:config HUSH_JOB
//config:	bool "Job control"
//config:	default y
//config:	depends on HUSH_INTERACTIVE
//config:	help
//config:	Enable job control: Ctrl-Z backgrounds, Ctrl-C interrupts current
//config:	command (not entire shell), fg/bg builtins work. Without this option,
//config:	"cmd &" still works by simply spawning a process and immediately
//config:	prompting for next command (or executing next command in a script),
//config:	but no separate process group is formed.
//config:
//config:config HUSH_TICK
//config:	bool "Support command substitution"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	Enable `command` and $(command).
//config:
//config:config HUSH_IF
//config:	bool "Support if/then/elif/else/fi"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_LOOPS
//config:	bool "Support for, while and until loops"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_CASE
//config:	bool "Support case ... esac statement"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	Enable case ... esac statement. +400 bytes.
//config:
//config:config HUSH_FUNCTIONS
//config:	bool "Support funcname() { commands; } syntax"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	Enable support for shell functions. +800 bytes.
//config:
//config:config HUSH_LOCAL
//config:	bool "local builtin"
//config:	default y
//config:	depends on HUSH_FUNCTIONS
//config:	help
//config:	Enable support for local variables in functions.
//config:
//config:config HUSH_RANDOM_SUPPORT
//config:	bool "Pseudorandom generator and $RANDOM variable"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	Enable pseudorandom generator and dynamic variable "$RANDOM".
//config:	Each read of "$RANDOM" will generate a new pseudorandom value.
//config:
//config:config HUSH_MODE_X
//config:	bool "Support 'hush -x' option and 'set -x' command"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	This instructs hush to print commands before execution.
//config:	Adds ~300 bytes.
//config:
//config:config HUSH_ECHO
//config:	bool "echo builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_PRINTF
//config:	bool "printf builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_TEST
//config:	bool "test builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_HELP
//config:	bool "help builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_EXPORT
//config:	bool "export builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_EXPORT_N
//config:	bool "Support 'export -n' option"
//config:	default y
//config:	depends on HUSH_EXPORT
//config:	help
//config:	export -n unexports variables. It is a bash extension.
//config:
//config:config HUSH_READONLY
//config:	bool "readonly builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:	help
//config:	Enable support for read-only variables.
//config:
//config:config HUSH_KILL
//config:	bool "kill builtin (supports kill %jobspec)"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_WAIT
//config:	bool "wait builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_COMMAND
//config:	bool "command builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_TRAP
//config:	bool "trap builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_TYPE
//config:	bool "type builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_TIMES
//config:	bool "times builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_READ
//config:	bool "read builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_SET
//config:	bool "set builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_UNSET
//config:	bool "unset builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_ULIMIT
//config:	bool "ulimit builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_UMASK
//config:	bool "umask builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_GETOPTS
//config:	bool "getopts builtin"
//config:	default y
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH
//config:
//config:config HUSH_MEMLEAK
//config:	bool "memleak builtin (debugging)"
//config:	default n
//config:	depends on HUSH || SH_IS_HUSH || BASH_IS_HUSH

//applet:IF_HUSH(APPLET(hush, BB_DIR_BIN, BB_SUID_DROP))
//                       APPLET_ODDNAME:name  main  location    suid_type     help
//applet:IF_SH_IS_HUSH(  APPLET_ODDNAME(sh,   hush, BB_DIR_BIN, BB_SUID_DROP, hush))
//applet:IF_BASH_IS_HUSH(APPLET_ODDNAME(bash, hush, BB_DIR_BIN, BB_SUID_DROP, hush))

//kbuild:lib-$(CONFIG_HUSH) += hush.o match.o shell_common.o
//kbuild:lib-$(CONFIG_SH_IS_HUSH) += hush.o match.o shell_common.o
//kbuild:lib-$(CONFIG_BASH_IS_HUSH) += hush.o match.o shell_common.o
//kbuild:lib-$(CONFIG_HUSH_RANDOM_SUPPORT) += random.o

/* -i (interactive) is also accepted,
 * but does nothing, therefore not shown in help.
 * NOMMU-specific options are not meant to be used by users,
 * therefore we don't show them either.
 */
//usage:#define hush_trivial_usage
//usage:	"[-enxl] [-c 'SCRIPT' [ARG0 [ARGS]] / FILE [ARGS] / -s [ARGS]]"
//usage:#define hush_full_usage "\n\n"
//usage:	"Unix shell interpreter"

#if !(defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) \
	|| defined(__APPLE__) \
    )
# include <malloc.h>   /* for malloc_trim */
#endif
#include <glob.h>
/* #include <dmalloc.h> */
#if ENABLE_HUSH_CASE
# include <fnmatch.h>
#endif
#include <sys/times.h>
#include <sys/utsname.h> /* for setting $HOSTNAME */

#include "busybox.h"  /* for APPLET_IS_NOFORK/NOEXEC */
#include "unicode.h"
#include "shell_common.h"
#include "math.h"
#include "match.h"
#if ENABLE_HUSH_RANDOM_SUPPORT
# include "random.h"
#else
# define CLEAR_RANDOM_T(rnd) ((void)0)
#endif
#ifndef O_CLOEXEC
# define O_CLOEXEC 0
#endif
#ifndef F_DUPFD_CLOEXEC
# define F_DUPFD_CLOEXEC F_DUPFD
#endif

#if ENABLE_FEATURE_SH_EMBEDDED_SCRIPTS && !(ENABLE_ASH || ENABLE_SH_IS_ASH || ENABLE_BASH_IS_ASH)
# include "embedded_scripts.h"
#else
# define NUM_SCRIPTS 0
#endif

/* So far, all bash compat is controlled by one config option */
/* Separate defines document which part of code implements what */
#define BASH_PATTERN_SUBST ENABLE_HUSH_BASH_COMPAT
#define BASH_SUBSTR        ENABLE_HUSH_BASH_COMPAT
#define BASH_SOURCE        ENABLE_HUSH_BASH_COMPAT
#define BASH_HOSTNAME_VAR  ENABLE_HUSH_BASH_COMPAT
#define BASH_EPOCH_VARS    ENABLE_HUSH_BASH_COMPAT
#define BASH_TEST2         (ENABLE_HUSH_BASH_COMPAT && ENABLE_HUSH_TEST)
#define BASH_READ_D        ENABLE_HUSH_BASH_COMPAT


/* Build knobs */
#define LEAK_HUNTING 0
#define BUILD_AS_NOMMU 0
/* Enable/disable sanity checks. Ok to enable in production,
 * only adds a bit of bloat. Set to >1 to get non-production level verbosity.
 * Keeping 1 for now even in released versions.
 */
#define HUSH_DEBUG 1
/* Slightly bigger (+200 bytes), but faster hush.
 * So far it only enables a trick with counting SIGCHLDs and forks,
 * which allows us to do fewer waitpid's.
 * (we can detect a case where neither forks were done nor SIGCHLDs happened
 * and therefore waitpid will return the same result as last time)
 */
#define ENABLE_HUSH_FAST 0
/* TODO: implement simplified code for users which do not need ${var%...} ops
 * So far ${var%...} ops are always enabled:
 */
#define ENABLE_HUSH_DOLLAR_OPS 1


#if BUILD_AS_NOMMU
# undef BB_MMU
# undef USE_FOR_NOMMU
# undef USE_FOR_MMU
# define BB_MMU 0
# define USE_FOR_NOMMU(...) __VA_ARGS__
# define USE_FOR_MMU(...)
#endif

#include "NUM_APPLETS.h"
#if NUM_APPLETS == 1
/* STANDALONE does not make sense, and won't compile */
# undef CONFIG_FEATURE_SH_STANDALONE
# undef ENABLE_FEATURE_SH_STANDALONE
# undef IF_FEATURE_SH_STANDALONE
# undef IF_NOT_FEATURE_SH_STANDALONE
# define ENABLE_FEATURE_SH_STANDALONE 0
# define IF_FEATURE_SH_STANDALONE(...)
# define IF_NOT_FEATURE_SH_STANDALONE(...) __VA_ARGS__
#endif

#if !ENABLE_HUSH_INTERACTIVE
# undef ENABLE_FEATURE_EDITING
# define ENABLE_FEATURE_EDITING 0
# undef ENABLE_FEATURE_EDITING_FANCY_PROMPT
# define ENABLE_FEATURE_EDITING_FANCY_PROMPT 0
# undef ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
# define ENABLE_FEATURE_EDITING_SAVE_ON_EXIT 0
#endif

/* Do we support ANY keywords? */
#if ENABLE_HUSH_IF || ENABLE_HUSH_LOOPS || ENABLE_HUSH_CASE
# define HAS_KEYWORDS 1
# define IF_HAS_KEYWORDS(...) __VA_ARGS__
# define IF_HAS_NO_KEYWORDS(...)
#else
# define HAS_KEYWORDS 0
# define IF_HAS_KEYWORDS(...)
# define IF_HAS_NO_KEYWORDS(...) __VA_ARGS__
#endif

/* If you comment out one of these below, it will be #defined later
 * to perform debug printfs to stderr: */
#define debug_printf(...)         do {} while (0)
/* Finer-grained debug switches */
#define debug_printf_parse(...)   do {} while (0)
#define debug_printf_heredoc(...) do {} while (0)
#define debug_print_tree(a, b)    do {} while (0)
#define debug_printf_exec(...)    do {} while (0)
#define debug_printf_env(...)     do {} while (0)
#define debug_printf_jobs(...)    do {} while (0)
#define debug_printf_expand(...)  do {} while (0)
#define debug_printf_varexp(...)  do {} while (0)
#define debug_printf_glob(...)    do {} while (0)
#define debug_printf_redir(...)   do {} while (0)
#define debug_printf_list(...)    do {} while (0)
#define debug_printf_subst(...)   do {} while (0)
#define debug_printf_prompt(...)  do {} while (0)
#define debug_printf_clean(...)   do {} while (0)

#define ERR_PTR ((void*)(long)1)

#define JOB_STATUS_FORMAT    "[%u] %-22s %.40s\n"

#define _SPECIAL_VARS_STR     "_*@$!?#-"
#define SPECIAL_VARS_STR     ("_*@$!?#-" + 1)
#define NUMERIC_SPECVARS_STR ("_*@$!?#-" + 3)
#if BASH_PATTERN_SUBST
/* Support / and // replace ops */
/* Note that // is stored as \ in "encoded" string representation */
# define VAR_ENCODED_SUBST_OPS      "\\/%#:-=+?"
# define VAR_SUBST_OPS             ("\\/%#:-=+?" + 1)
# define MINUS_PLUS_EQUAL_QUESTION ("\\/%#:-=+?" + 5)
#else
# define VAR_ENCODED_SUBST_OPS      "%#:-=+?"
# define VAR_SUBST_OPS              "%#:-=+?"
# define MINUS_PLUS_EQUAL_QUESTION ("%#:-=+?" + 3)
#endif

#define SPECIAL_VAR_SYMBOL_STR "\3"
#define SPECIAL_VAR_SYMBOL       3
/* The "variable" with name "\1" emits string "\3". Testcase: "echo ^C" */
#define SPECIAL_VAR_QUOTED_SVS   1

struct variable;

static const char hush_version_str[] ALIGN1 = "HUSH_VERSION="BB_VER;

/* This supports saving pointers malloced in vfork child,
 * to be freed in the parent.
 */
#if !BB_MMU
typedef struct nommu_save_t {
	struct variable *old_vars;
	char **argv;
	char **argv_from_re_execing;
} nommu_save_t;
#endif

enum {
	RES_NONE  = 0,
#if ENABLE_HUSH_IF
	RES_IF    ,
	RES_THEN  ,
	RES_ELIF  ,
	RES_ELSE  ,
	RES_FI    ,
#endif
#if ENABLE_HUSH_LOOPS
	RES_FOR   ,
	RES_WHILE ,
	RES_UNTIL ,
	RES_DO    ,
	RES_DONE  ,
#endif
#if ENABLE_HUSH_LOOPS || ENABLE_HUSH_CASE
	RES_IN    ,
#endif
#if ENABLE_HUSH_CASE
	RES_CASE  ,
	/* three pseudo-keywords support contrived "case" syntax: */
	RES_CASE_IN,   /* "case ... IN", turns into RES_MATCH when IN is observed */
	RES_MATCH ,    /* "word)" */
	RES_CASE_BODY, /* "this command is inside CASE" */
	RES_ESAC  ,
#endif
	RES_XXXX  ,
	RES_SNTX
};

typedef struct o_string {
	char *data;
	int length; /* position where data is appended */
	int maxlen;
	int o_expflags;
	/* At least some part of the string was inside '' or "",
	 * possibly empty one: word"", wo''rd etc. */
	smallint has_quoted_part;
	smallint has_empty_slot;
	smallint ended_in_ifs;
} o_string;
enum {
	EXP_FLAG_SINGLEWORD     = 0x80, /* must be 0x80 */
	EXP_FLAG_GLOB           = 0x2,
	/* Protect newly added chars against globbing
	 * by prepending \ to *, ?, [, \ */
	EXP_FLAG_ESC_GLOB_CHARS = 0x1,
};
/* Used for initialization: o_string foo = NULL_O_STRING; */
#define NULL_O_STRING { NULL }

#ifndef debug_printf_parse
static const char *const assignment_flag[] = {
	"MAYBE_ASSIGNMENT",
	"DEFINITELY_ASSIGNMENT",
	"NOT_ASSIGNMENT",
	"WORD_IS_KEYWORD",
};
#endif

/* We almost can use standard FILE api, but we need an ability to move
 * its fd when redirects coincide with it. No api exists for that
 * (RFE for it at https://sourceware.org/bugzilla/show_bug.cgi?id=21902).
 * HFILE is our internal alternative. Only supports reading.
 * Since we now can, we incorporate linked list of all opened HFILEs
 * into the struct (used to be a separate mini-list).
 */
typedef struct HFILE {
	char *cur;
	char *end;
	struct HFILE *next_hfile;
	int fd;
	char buf[1024];
} HFILE;

typedef struct in_str {
	const char *p;
	int peek_buf[2];
	int last_char;
	HFILE *file;
} in_str;

/* The descrip member of this structure is only used to make
 * debugging output pretty */
static const struct {
	int mode;
	signed char default_fd;
	char descrip[3];
} redir_table[] = {
	{ O_RDONLY,                  0, "<"  },
	{ O_CREAT|O_TRUNC|O_WRONLY,  1, ">"  },
	{ O_CREAT|O_APPEND|O_WRONLY, 1, ">>" },
	{ O_CREAT|O_RDWR,            1, "<>" },
	{ O_RDONLY,                  0, "<<" },
/* Should not be needed. Bogus default_fd helps in debugging */
/*	{ O_RDONLY,                 77, "<<" }, */
};

struct redir_struct {
	struct redir_struct *next;
	char *rd_filename;          /* filename */
	int rd_fd;                  /* fd to redirect */
	/* fd to redirect to, or -3 if rd_fd is to be closed (n>&-) */
	int rd_dup;
	smallint rd_type;           /* (enum redir_type) */
	/* note: for heredocs, rd_filename contains heredoc delimiter,
	 * and subsequently heredoc itself; and rd_dup is a bitmask:
	 * bit 0: do we need to trim leading tabs?
	 * bit 1: is heredoc quoted (<<'delim' syntax) ?
	 */
};
typedef enum redir_type {
	REDIRECT_INPUT     = 0,
	REDIRECT_OVERWRITE = 1,
	REDIRECT_APPEND    = 2,
	REDIRECT_IO        = 3,
	REDIRECT_HEREDOC   = 4,
	REDIRECT_HEREDOC2  = 5, /* REDIRECT_HEREDOC after heredoc is loaded */

	REDIRFD_CLOSE      = -3,
	REDIRFD_SYNTAX_ERR = -2,
	REDIRFD_TO_FILE    = -1,
	/* otherwise, rd_fd is redirected to rd_dup */

	HEREDOC_SKIPTABS = 1,
	HEREDOC_QUOTED   = 2,
} redir_type;


struct command {
	pid_t pid;                  /* 0 if exited */
	unsigned assignment_cnt;    /* how many argv[i] are assignments? */
#if ENABLE_HUSH_LINENO_VAR
	unsigned lineno;
#endif
	smallint cmd_type;          /* CMD_xxx */
#define CMD_NORMAL   0
#define CMD_SUBSHELL 1
#if BASH_TEST2 || ENABLE_HUSH_LOCAL || ENABLE_HUSH_EXPORT || ENABLE_HUSH_READONLY
/* used for "[[ EXPR ]]", and to prevent word splitting and globbing in
 * "export v=t*"
 */
# define CMD_SINGLEWORD_NOGLOB 2
#endif
#if ENABLE_HUSH_FUNCTIONS
# define CMD_FUNCDEF 3
#endif

	smalluint cmd_exitcode;
	/* if non-NULL, this "command" is { list }, ( list ), or a compound statement */
	struct pipe *group;
#if !BB_MMU
	char *group_as_string;
#endif
#if ENABLE_HUSH_FUNCTIONS
	struct function *child_func;
/* This field is used to prevent a bug here:
 * while...do f1() {a;}; f1; f1() {b;}; f1; done
 * When we execute "f1() {a;}" cmd, we create new function and clear
 * cmd->group, cmd->group_as_string, cmd->argv[0].
 * When we execute "f1() {b;}", we notice that f1 exists,
 * and that its "parent cmd" struct is still "alive",
 * we put those fields back into cmd->xxx
 * (struct function has ->parent_cmd ptr to facilitate that).
 * When we loop back, we can execute "f1() {a;}" again and set f1 correctly.
 * Without this trick, loop would execute a;b;b;b;...
 * instead of correct sequence a;b;a;b;...
 * When command is freed, it severs the link
 * (sets ->child_func->parent_cmd to NULL).
 */
#endif
	char **argv;                /* command name and arguments */
/* argv vector may contain variable references (^Cvar^C, ^C0^C etc)
 * and on execution these are substituted with their values.
 * Substitution can make _several_ words out of one argv[n]!
 * Example: argv[0]=='.^C*^C.' here: echo .$*.
 * References of the form ^C`cmd arg^C are `cmd arg` substitutions.
 */
	struct redir_struct *redirects; /* I/O redirections */
};
/* Is there anything in this command at all? */
#define IS_NULL_CMD(cmd) \
	(!(cmd)->group && !(cmd)->argv && !(cmd)->redirects)

struct pipe {
	struct pipe *next;
	int num_cmds;               /* total number of commands in pipe */
	int alive_cmds;             /* number of commands running (not exited) */
	int stopped_cmds;           /* number of commands alive, but stopped */
#if ENABLE_HUSH_JOB
	unsigned jobid;             /* job number */
	pid_t pgrp;                 /* process group ID for the job */
	char *cmdtext;              /* name of job */
#endif
	struct command *cmds;       /* array of commands in pipe */
	smallint followup;          /* PIPE_BG, PIPE_SEQ, PIPE_OR, PIPE_AND */
	IF_HAS_KEYWORDS(smallint pi_inverted;) /* "! cmd | cmd" */
	IF_HAS_KEYWORDS(smallint res_word;) /* needed for if, for, while, until... */
};
typedef enum pipe_style {
	PIPE_SEQ = 0,
	PIPE_AND = 1,
	PIPE_OR  = 2,
	PIPE_BG  = 3,
} pipe_style;
/* Is there anything in this pipe at all? */
#define IS_NULL_PIPE(pi) \
	((pi)->num_cmds == 0 IF_HAS_KEYWORDS( && (pi)->res_word == RES_NONE))

/* This holds pointers to the various results of parsing */
struct parse_context {
	/* linked list of pipes */
	struct pipe *list_head;
	/* last pipe (being constructed right now) */
	struct pipe *pipe;
	/* last command in pipe (being constructed right now) */
	struct command *command;
	/* last redirect in command->redirects list */
	struct redir_struct *pending_redirect;
	o_string word;
#if !BB_MMU
	o_string as_string;
#endif
	smallint is_assignment; /* 0:maybe, 1:yes, 2:no, 3:keyword */
#if HAS_KEYWORDS
	smallint ctx_res_w;
	smallint ctx_inverted; /* "! cmd | cmd" */
#if ENABLE_HUSH_CASE
	smallint ctx_dsemicolon; /* ";;" seen */
#endif
	/* bitmask of FLAG_xxx, for figuring out valid reserved words */
	int old_flag;
	/* group we are enclosed in:
	 * example: "if pipe1; pipe2; then pipe3; fi"
	 * when we see "if" or "then", we malloc and copy current context,
	 * and make ->stack point to it. then we parse pipeN.
	 * when closing "then" / fi" / whatever is found,
	 * we move list_head into ->stack->command->group,
	 * copy ->stack into current context, and delete ->stack.
	 * (parsing of { list } and ( list ) doesn't use this method)
	 */
	struct parse_context *stack;
#endif
};
enum {
	MAYBE_ASSIGNMENT      = 0,
	DEFINITELY_ASSIGNMENT = 1,
	NOT_ASSIGNMENT        = 2,
	/* Not an assignment, but next word may be: "if v=xyz cmd;" */
	WORD_IS_KEYWORD       = 3,
};

/* On program start, environ points to initial environment.
 * putenv adds new pointers into it, unsetenv removes them.
 * Neither of these (de)allocates the strings.
 * setenv allocates new strings in malloc space and does putenv,
 * and thus setenv is unusable (leaky) for shell's purposes */
#define setenv(...) setenv_is_leaky_dont_use()
struct variable {
	struct variable *next;
	char *varstr;        /* points to "name=" portion */
	int max_len;         /* if > 0, name is part of initial env; else name is malloced */
	uint16_t var_nest_level;
	smallint flg_export; /* putenv should be done on this var */
	smallint flg_read_only;
};

enum {
	BC_BREAK = 1,
	BC_CONTINUE = 2,
};

#if ENABLE_HUSH_FUNCTIONS
struct function {
	struct function *next;
	char *name;
	struct command *parent_cmd;
	struct pipe *body;
# if !BB_MMU
	char *body_as_string;
# endif
};
#endif


/* set -/+o OPT support. (TODO: make it optional)
 * bash supports the following opts:
 * allexport       off
 * braceexpand     on
 * emacs           on
 * errexit         off
 * errtrace        off
 * functrace       off
 * hashall         on
 * histexpand      off
 * history         on
 * ignoreeof       off
 * interactive-comments    on
 * keyword         off
 * monitor         on
 * noclobber       off
 * noexec          off
 * noglob          off
 * nolog           off
 * notify          off
 * nounset         off
 * onecmd          off
 * physical        off
 * pipefail        off
 * posix           off
 * privileged      off
 * verbose         off
 * vi              off
 * xtrace          off
 */
static const char o_opt_strings[] ALIGN1 =
	"pipefail\0"
	"noexec\0"
	"errexit\0"
#if ENABLE_HUSH_MODE_X
	"xtrace\0"
#endif
	;
enum {
	OPT_O_PIPEFAIL,
	OPT_O_NOEXEC,
	OPT_O_ERREXIT,
#if ENABLE_HUSH_MODE_X
	OPT_O_XTRACE,
#endif
	NUM_OPT_O
};

/* "Globals" within this file */
/* Sorted roughly by size (smaller offsets == smaller code) */
struct globals {
	/* interactive_fd != 0 means we are an interactive shell.
	 * If we are, then saved_tty_pgrp can also be != 0, meaning
	 * that controlling tty is available. With saved_tty_pgrp == 0,
	 * job control still works, but terminal signals
	 * (^C, ^Z, ^Y, ^\) won't work at all, and background
	 * process groups can only be created with "cmd &".
	 * With saved_tty_pgrp != 0, hush will use tcsetpgrp()
	 * to give tty to the foreground process group,
	 * and will take it back when the group is stopped (^Z)
	 * or killed (^C).
	 */
#if ENABLE_HUSH_INTERACTIVE
	/* 'interactive_fd' is a fd# open to ctty, if we have one
	 * _AND_ if we decided to act interactively */
	int interactive_fd;
	IF_NOT_FEATURE_EDITING_FANCY_PROMPT(char *PS1;)
# define G_interactive_fd (G.interactive_fd)
#else
# define G_interactive_fd 0
#endif
#if ENABLE_FEATURE_EDITING
	line_input_t *line_input_state;
#endif
	pid_t root_pid;
	pid_t root_ppid;
	pid_t last_bg_pid;
#if ENABLE_HUSH_RANDOM_SUPPORT
	random_t random_gen;
#endif
#if ENABLE_HUSH_JOB
	int run_list_level;
	unsigned last_jobid;
	pid_t saved_tty_pgrp;
	struct pipe *job_list;
# define G_saved_tty_pgrp (G.saved_tty_pgrp)
#else
# define G_saved_tty_pgrp 0
#endif
	/* How deeply are we in context where "set -e" is ignored */
	int errexit_depth;
	/* "set -e" rules (do we follow them correctly?):
	 * Exit if pipe, list, or compound command exits with a non-zero status.
	 * Shell does not exit if failed command is part of condition in
	 * if/while, part of && or || list except the last command, any command
	 * in a pipe but the last, or if the command's return value is being
	 * inverted with !. If a compound command other than a subshell returns a
	 * non-zero status because a command failed while -e was being ignored, the
	 * shell does not exit. A trap on ERR, if set, is executed before the shell
	 * exits [ERR is a bashism].
	 *
	 * If a compound command or function executes in a context where -e is
	 * ignored, none of the commands executed within are affected by the -e
	 * setting. If a compound command or function sets -e while executing in a
	 * context where -e is ignored, that setting does not have any effect until
	 * the compound command or the command containing the function call completes.
	 */

	char o_opt[NUM_OPT_O];
#if ENABLE_HUSH_MODE_X
# define G_x_mode (G.o_opt[OPT_O_XTRACE])
#else
# define G_x_mode 0
#endif
	char opt_s;
	char opt_c;
#if ENABLE_HUSH_INTERACTIVE
	smallint promptmode; /* 0: PS1, 1: PS2 */
#endif
	smallint flag_SIGINT;
#if ENABLE_HUSH_LOOPS
	smallint flag_break_continue;
#endif
#if ENABLE_HUSH_FUNCTIONS
	/* 0: outside of a function (or sourced file)
	 * -1: inside of a function, ok to use return builtin
	 * 1: return is invoked, skip all till end of func
	 */
	smallint flag_return_in_progress;
# define G_flag_return_in_progress (G.flag_return_in_progress)
#else
# define G_flag_return_in_progress 0
#endif
	smallint exiting; /* used to prevent EXIT trap recursion */
	/* These support $? */
	smalluint last_exitcode;
	smalluint expand_exitcode;
	smalluint last_bg_pid_exitcode;
#if ENABLE_HUSH_SET
	/* are global_argv and global_argv[1..n] malloced? (note: not [0]) */
	smalluint global_args_malloced;
# define G_global_args_malloced (G.global_args_malloced)
#else
# define G_global_args_malloced 0
#endif
#if ENABLE_HUSH_BASH_COMPAT
	int dead_job_exitcode; /* for "wait -n" */
#endif
	/* how many non-NULL argv's we have. NB: $# + 1 */
	int global_argc;
	char **global_argv;
#if !BB_MMU
	char *argv0_for_re_execing;
#endif
#if ENABLE_HUSH_LOOPS
	unsigned depth_break_continue;
	unsigned depth_of_loop;
#endif
#if ENABLE_HUSH_GETOPTS
	unsigned getopt_count;
#endif
	const char *ifs;
	char *ifs_whitespace; /* = G.ifs or malloced */
	const char *cwd;
	struct variable *top_var;
	char **expanded_assignments;
	struct variable **shadowed_vars_pp;
	unsigned var_nest_level;
#if ENABLE_HUSH_FUNCTIONS
# if ENABLE_HUSH_LOCAL
	unsigned func_nest_level; /* solely to prevent "local v" in non-functions */
# endif
	struct function *top_func;
#endif
	/* Signal and trap handling */
#if ENABLE_HUSH_FAST
	unsigned count_SIGCHLD;
	unsigned handled_SIGCHLD;
	smallint we_have_children;
#endif
#if ENABLE_HUSH_LINENO_VAR
	unsigned parse_lineno;
	unsigned execute_lineno;
#endif
	HFILE *HFILE_list;
	HFILE *HFILE_stdin;
	/* Which signals have non-DFL handler (even with no traps set)?
	 * Set at the start to:
	 * (SIGQUIT + maybe SPECIAL_INTERACTIVE_SIGS + maybe SPECIAL_JOBSTOP_SIGS)
	 * SPECIAL_INTERACTIVE_SIGS are cleared after fork.
	 * The rest is cleared right before execv syscalls.
	 * Other than these two times, never modified.
	 */
	unsigned special_sig_mask;
#if ENABLE_HUSH_JOB
	unsigned fatal_sig_mask;
# define G_fatal_sig_mask (G.fatal_sig_mask)
#else
# define G_fatal_sig_mask 0
#endif
#if ENABLE_HUSH_TRAP
	int pre_trap_exitcode;
# if ENABLE_HUSH_FUNCTIONS
	int return_exitcode;
# endif
	char **traps; /* char *traps[NSIG] */
# define G_traps G.traps
#else
# define G_traps ((char**)NULL)
#endif
	sigset_t pending_set;
#if ENABLE_HUSH_MEMLEAK
	unsigned long memleak_value;
#endif
#if ENABLE_HUSH_MODE_X
	unsigned x_mode_depth;
	/* "set -x" output should not be redirectable with subsequent 2>FILE.
	 * We dup fd#2 to x_mode_fd when "set -x" is executed, and use it
	 * for all subsequent output.
	 */
	int x_mode_fd;
	o_string x_mode_buf;
#endif
#if HUSH_DEBUG >= 2
	int debug_indent;
#endif
	struct sigaction sa;
	char optstring_buf[sizeof("eixcs")];
#if BASH_EPOCH_VARS
	char epoch_buf[sizeof("%lu.nnnnnn") + sizeof(long)*3];
#endif
#if ENABLE_FEATURE_EDITING
	char user_input_buf[CONFIG_FEATURE_EDITING_MAX_LEN];
#endif
};
#define G (*ptr_to_globals)
/* Not #defining name to G.name - this quickly gets unwieldy
 * (too many defines). Also, I actually prefer to see when a variable
 * is global, thus "G." prefix is a useful hint */
#define INIT_G() do { \
	SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
	/* memset(&G.sa, 0, sizeof(G.sa)); */  \
	sigfillset(&G.sa.sa_mask); \
	G.sa.sa_flags = SA_RESTART; \
} while (0)


/* Function prototypes for builtins */
static int builtin_cd(char **argv) FAST_FUNC;
#if ENABLE_HUSH_ECHO
static int builtin_echo(char **argv) FAST_FUNC;
#endif
static int builtin_eval(char **argv) FAST_FUNC;
static int builtin_exec(char **argv) FAST_FUNC;
static int builtin_exit(char **argv) FAST_FUNC;
#if ENABLE_HUSH_EXPORT
static int builtin_export(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_READONLY
static int builtin_readonly(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_JOB
static int builtin_fg_bg(char **argv) FAST_FUNC;
static int builtin_jobs(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_GETOPTS
static int builtin_getopts(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_HELP
static int builtin_help(char **argv) FAST_FUNC;
#endif
#if MAX_HISTORY && ENABLE_FEATURE_EDITING
static int builtin_history(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_LOCAL
static int builtin_local(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_MEMLEAK
static int builtin_memleak(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_PRINTF
static int builtin_printf(char **argv) FAST_FUNC;
#endif
static int builtin_pwd(char **argv) FAST_FUNC;
#if ENABLE_HUSH_READ
static int builtin_read(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_SET
static int builtin_set(char **argv) FAST_FUNC;
#endif
static int builtin_shift(char **argv) FAST_FUNC;
static int builtin_source(char **argv) FAST_FUNC;
#if ENABLE_HUSH_TEST || BASH_TEST2
static int builtin_test(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_TRAP
static int builtin_trap(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_TYPE
static int builtin_type(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_TIMES
static int builtin_times(char **argv) FAST_FUNC;
#endif
static int builtin_true(char **argv) FAST_FUNC;
#if ENABLE_HUSH_UMASK
static int builtin_umask(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_UNSET
static int builtin_unset(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_KILL
static int builtin_kill(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_WAIT
static int builtin_wait(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_LOOPS
static int builtin_break(char **argv) FAST_FUNC;
static int builtin_continue(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_FUNCTIONS
static int builtin_return(char **argv) FAST_FUNC;
#endif

/* Table of built-in functions.  They can be forked or not, depending on
 * context: within pipes, they fork.  As simple commands, they do not.
 * When used in non-forking context, they can change global variables
 * in the parent shell process.  If forked, of course they cannot.
 * For example, 'unset foo | whatever' will parse and run, but foo will
 * still be set at the end. */
struct built_in_command {
	const char *b_cmd;
	int (*b_function)(char **argv) FAST_FUNC;
#if ENABLE_HUSH_HELP
	const char *b_descr;
# define BLTIN(cmd, func, help) { cmd, func, help }
#else
# define BLTIN(cmd, func, help) { cmd, func }
#endif
};

static const struct built_in_command bltins1[] = {
	BLTIN("."        , builtin_source  , "Run commands in file"),
	BLTIN(":"        , builtin_true    , NULL),
#if ENABLE_HUSH_JOB
	BLTIN("bg"       , builtin_fg_bg   , "Resume job in background"),
#endif
#if ENABLE_HUSH_LOOPS
	BLTIN("break"    , builtin_break   , "Exit loop"),
#endif
	BLTIN("cd"       , builtin_cd      , "Change directory"),
#if ENABLE_HUSH_LOOPS
	BLTIN("continue" , builtin_continue, "Start new loop iteration"),
#endif
	BLTIN("eval"     , builtin_eval    , "Construct and run shell command"),
	BLTIN("exec"     , builtin_exec    , "Execute command, don't return to shell"),
	BLTIN("exit"     , builtin_exit    , NULL),
#if ENABLE_HUSH_EXPORT
	BLTIN("export"   , builtin_export  , "Set environment variables"),
#endif
#if ENABLE_HUSH_JOB
	BLTIN("fg"       , builtin_fg_bg   , "Bring job to foreground"),
#endif
#if ENABLE_HUSH_GETOPTS
	BLTIN("getopts"  , builtin_getopts , NULL),
#endif
#if ENABLE_HUSH_HELP
	BLTIN("help"     , builtin_help    , NULL),
#endif
#if MAX_HISTORY && ENABLE_FEATURE_EDITING
	BLTIN("history"  , builtin_history , "Show history"),
#endif
#if ENABLE_HUSH_JOB
	BLTIN("jobs"     , builtin_jobs    , "List jobs"),
#endif
#if ENABLE_HUSH_KILL
	BLTIN("kill"     , builtin_kill    , "Send signals to processes"),
#endif
#if ENABLE_HUSH_LOCAL
	BLTIN("local"    , builtin_local   , "Set local variables"),
#endif
#if ENABLE_HUSH_MEMLEAK
	BLTIN("memleak"  , builtin_memleak , NULL),
#endif
#if ENABLE_HUSH_READ
	BLTIN("read"     , builtin_read    , "Input into variable"),
#endif
#if ENABLE_HUSH_READONLY
	BLTIN("readonly" , builtin_readonly, "Make variables read-only"),
#endif
#if ENABLE_HUSH_FUNCTIONS
	BLTIN("return"   , builtin_return  , "Return from function"),
#endif
#if ENABLE_HUSH_SET
	BLTIN("set"      , builtin_set     , "Set positional parameters"),
#endif
	BLTIN("shift"    , builtin_shift   , "Shift positional parameters"),
#if BASH_SOURCE
	BLTIN("source"   , builtin_source  , NULL),
#endif
#if ENABLE_HUSH_TIMES
	BLTIN("times"    , builtin_times   , NULL),
#endif
#if ENABLE_HUSH_TRAP
	BLTIN("trap"     , builtin_trap    , "Trap signals"),
#endif
	BLTIN("true"     , builtin_true    , NULL),
#if ENABLE_HUSH_TYPE
	BLTIN("type"     , builtin_type    , "Show command type"),
#endif
#if ENABLE_HUSH_ULIMIT
	BLTIN("ulimit"   , shell_builtin_ulimit, "Control resource limits"),
#endif
#if ENABLE_HUSH_UMASK
	BLTIN("umask"    , builtin_umask   , "Set file creation mask"),
#endif
#if ENABLE_HUSH_UNSET
	BLTIN("unset"    , builtin_unset   , "Unset variables"),
#endif
#if ENABLE_HUSH_WAIT
	BLTIN("wait"     , builtin_wait    , "Wait for process to finish"),
#endif
};
/* These builtins won't be used if we are on NOMMU and need to re-exec
 * (it's cheaper to run an external program in this case):
 */
static const struct built_in_command bltins2[] = {
#if ENABLE_HUSH_TEST
	BLTIN("["        , builtin_test    , NULL),
#endif
#if BASH_TEST2
	BLTIN("[["       , builtin_test    , NULL),
#endif
#if ENABLE_HUSH_ECHO
	BLTIN("echo"     , builtin_echo    , NULL),
#endif
#if ENABLE_HUSH_PRINTF
	BLTIN("printf"   , builtin_printf  , NULL),
#endif
	BLTIN("pwd"      , builtin_pwd     , NULL),
#if ENABLE_HUSH_TEST
	BLTIN("test"     , builtin_test    , NULL),
#endif
};


/* Debug printouts.
 */
#if HUSH_DEBUG >= 2
/* prevent disasters with G.debug_indent < 0 */
# define indent() fdprintf(2, "%*s", (G.debug_indent * 2) & 0xff, "")
# define debug_enter() (G.debug_indent++)
# define debug_leave() (G.debug_indent--)
#else
# define indent()      ((void)0)
# define debug_enter() ((void)0)
# define debug_leave() ((void)0)
#endif

#ifndef debug_printf
# define debug_printf(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_parse
# define debug_printf_parse(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_heredoc
# define debug_printf_heredoc(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_exec
#define debug_printf_exec(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_env
# define debug_printf_env(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_jobs
# define debug_printf_jobs(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_JOBS 1
#else
# define DEBUG_JOBS 0
#endif

#ifndef debug_printf_expand
# define debug_printf_expand(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_EXPAND 1
#else
# define DEBUG_EXPAND 0
#endif

#ifndef debug_printf_varexp
# define debug_printf_varexp(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_glob
# define debug_printf_glob(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_GLOB 1
#else
# define DEBUG_GLOB 0
#endif

#ifndef debug_printf_redir
# define debug_printf_redir(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_list
# define debug_printf_list(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_subst
# define debug_printf_subst(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_prompt
# define debug_printf_prompt(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_clean
# define debug_printf_clean(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_CLEAN 1
#else
# define DEBUG_CLEAN 0
#endif

#if DEBUG_EXPAND
static void debug_print_strings(const char *prefix, char **vv)
{
	indent();
	fdprintf(2, "%s:\n", prefix);
	while (*vv)
		fdprintf(2, " '%s'\n", *vv++);
}
#else
# define debug_print_strings(prefix, vv) ((void)0)
#endif


/* Leak hunting. Use hush_leaktool.sh for post-processing.
 */
#if LEAK_HUNTING
static void *xxmalloc(int lineno, size_t size)
{
	void *ptr = xmalloc((size + 0xff) & ~0xff);
	fdprintf(2, "line %d: malloc %p\n", lineno, ptr);
	return ptr;
}
static void *xxrealloc(int lineno, void *ptr, size_t size)
{
	ptr = xrealloc(ptr, (size + 0xff) & ~0xff);
	fdprintf(2, "line %d: realloc %p\n", lineno, ptr);
	return ptr;
}
static char *xxstrdup(int lineno, const char *str)
{
	char *ptr = xstrdup(str);
	fdprintf(2, "line %d: strdup %p\n", lineno, ptr);
	return ptr;
}
static void xxfree(void *ptr)
{
	fdprintf(2, "free %p\n", ptr);
	free(ptr);
}
# define xmalloc(s)     xxmalloc(__LINE__, s)
# define xrealloc(p, s) xxrealloc(__LINE__, p, s)
# define xstrdup(s)     xxstrdup(__LINE__, s)
# define free(p)        xxfree(p)
#endif


/* Syntax and runtime errors. They always abort scripts.
 * In interactive use they usually discard unparsed and/or unexecuted commands
 * and return to the prompt.
 * HUSH_DEBUG >= 2 prints line number in this file where it was detected.
 */
#if HUSH_DEBUG < 2
# define msg_and_die_if_script(lineno, ...)     msg_and_die_if_script(__VA_ARGS__)
# define syntax_error(lineno, msg)              syntax_error(msg)
# define syntax_error_at(lineno, msg)           syntax_error_at(msg)
# define syntax_error_unterm_ch(lineno, ch)     syntax_error_unterm_ch(ch)
# define syntax_error_unterm_str(lineno, s)     syntax_error_unterm_str(s)
# define syntax_error_unexpected_ch(lineno, ch) syntax_error_unexpected_ch(ch)
#endif

static void die_if_script(void)
{
	if (!G_interactive_fd) {
		if (G.last_exitcode) /* sometines it's 2, not 1 (bash compat) */
			xfunc_error_retval = G.last_exitcode;
		xfunc_die();
	}
}

static void msg_and_die_if_script(unsigned lineno, const char *fmt, ...)
{
	va_list p;

#if HUSH_DEBUG >= 2
	bb_error_msg("hush.c:%u", lineno);
#endif
	va_start(p, fmt);
	bb_verror_msg(fmt, p, NULL);
	va_end(p);
	die_if_script();
}

static void syntax_error(unsigned lineno UNUSED_PARAM, const char *msg)
{
	if (msg)
		bb_error_msg("syntax error: %s", msg);
	else
		bb_simple_error_msg("syntax error");
	die_if_script();
}

static void syntax_error_at(unsigned lineno UNUSED_PARAM, const char *msg)
{
	bb_error_msg("syntax error at '%s'", msg);
	die_if_script();
}

static void syntax_error_unterm_str(unsigned lineno UNUSED_PARAM, const char *s)
{
	bb_error_msg("syntax error: unterminated %s", s);
//? source4.tests fails: in bash, echo ${^} in script does not terminate the script
//	die_if_script();
}

static void syntax_error_unterm_ch(unsigned lineno, char ch)
{
	char msg[2] = { ch, '\0' };
	syntax_error_unterm_str(lineno, msg);
}

static void syntax_error_unexpected_ch(unsigned lineno UNUSED_PARAM, int ch)
{
	char msg[2];
	msg[0] = ch;
	msg[1] = '\0';
#if HUSH_DEBUG >= 2
	bb_error_msg("hush.c:%u", lineno);
#endif
	bb_error_msg("syntax error: unexpected %s", ch == EOF ? "EOF" : msg);
	die_if_script();
}

#if HUSH_DEBUG < 2
# undef msg_and_die_if_script
# undef syntax_error
# undef syntax_error_at
# undef syntax_error_unterm_ch
# undef syntax_error_unterm_str
# undef syntax_error_unexpected_ch
#else
# define msg_and_die_if_script(...)     msg_and_die_if_script(__LINE__, __VA_ARGS__)
# define syntax_error(msg)              syntax_error(__LINE__, msg)
# define syntax_error_at(msg)           syntax_error_at(__LINE__, msg)
# define syntax_error_unterm_ch(ch)     syntax_error_unterm_ch(__LINE__, ch)
# define syntax_error_unterm_str(s)     syntax_error_unterm_str(__LINE__, s)
# define syntax_error_unexpected_ch(ch) syntax_error_unexpected_ch(__LINE__, ch)
#endif


/* Utility functions
 */
/* Replace each \x with x in place, return ptr past NUL. */
static char *unbackslash(char *src)
{
	char *dst = src = strchrnul(src, '\\');
	while (1) {
		if (*src == '\\') {
			src++;
			if (*src != '\0') {
				/* \x -> x */
				*dst++ = *src++;
				continue;
			}
			/* else: "\<nul>". Do not delete this backslash.
			 * Testcase: eval 'echo ok\'
			 */
			*dst++ = '\\';
			/* fallthrough */
		}
		if ((*dst++ = *src++) == '\0')
			break;
	}
	return dst;
}

static char **add_strings_to_strings(char **strings, char **add, int need_to_dup)
{
	int i;
	unsigned count1;
	unsigned count2;
	char **v;

	v = strings;
	count1 = 0;
	if (v) {
		while (*v) {
			count1++;
			v++;
		}
	}
	count2 = 0;
	v = add;
	while (*v) {
		count2++;
		v++;
	}
	v = xrealloc(strings, (count1 + count2 + 1) * sizeof(char*));
	v[count1 + count2] = NULL;
	i = count2;
	while (--i >= 0)
		v[count1 + i] = (need_to_dup ? xstrdup(add[i]) : add[i]);
	return v;
}
#if LEAK_HUNTING
static char **xx_add_strings_to_strings(int lineno, char **strings, char **add, int need_to_dup)
{
	char **ptr = add_strings_to_strings(strings, add, need_to_dup);
	fdprintf(2, "line %d: add_strings_to_strings %p\n", lineno, ptr);
	return ptr;
}
#define add_strings_to_strings(strings, add, need_to_dup) \
	xx_add_strings_to_strings(__LINE__, strings, add, need_to_dup)
#endif

/* Note: takes ownership of "add" ptr (it is not strdup'ed) */
static char **add_string_to_strings(char **strings, char *add)
{
	char *v[2];
	v[0] = add;
	v[1] = NULL;
	return add_strings_to_strings(strings, v, /*dup:*/ 0);
}
#if LEAK_HUNTING
static char **xx_add_string_to_strings(int lineno, char **strings, char *add)
{
	char **ptr = add_string_to_strings(strings, add);
	fdprintf(2, "line %d: add_string_to_strings %p\n", lineno, ptr);
	return ptr;
}
#define add_string_to_strings(strings, add) \
	xx_add_string_to_strings(__LINE__, strings, add)
#endif

static void free_strings(char **strings)
{
	char **v;

	if (!strings)
		return;
	v = strings;
	while (*v) {
		free(*v);
		v++;
	}
	free(strings);
}

static int dup_CLOEXEC(int fd, int avoid_fd)
{
	int newfd;
 repeat:
	newfd = fcntl(fd, F_DUPFD_CLOEXEC, avoid_fd + 1);
	if (newfd >= 0) {
		if (F_DUPFD_CLOEXEC == F_DUPFD) /* if old libc (w/o F_DUPFD_CLOEXEC) */
			fcntl(newfd, F_SETFD, FD_CLOEXEC);
	} else { /* newfd < 0 */
		if (errno == EBUSY)
			goto repeat;
		if (errno == EINTR)
			goto repeat;
	}
	return newfd;
}

static int xdup_CLOEXEC_and_close(int fd, int avoid_fd)
{
	int newfd;
 repeat:
	newfd = fcntl(fd, F_DUPFD_CLOEXEC, avoid_fd + 1);
	if (newfd < 0) {
		if (errno == EBUSY)
			goto repeat;
		if (errno == EINTR)
			goto repeat;
		/* fd was not open? */
		if (errno == EBADF)
			return fd;
		xfunc_die();
	}
	if (F_DUPFD_CLOEXEC == F_DUPFD) /* if old libc (w/o F_DUPFD_CLOEXEC) */
		fcntl(newfd, F_SETFD, FD_CLOEXEC);
	close(fd);
	return newfd;
}


/* Manipulating HFILEs */
static HFILE *hfopen(const char *name)
{
	HFILE *fp;
	int fd;

	fd = STDIN_FILENO;
	if (name) {
		fd = open(name, O_RDONLY | O_CLOEXEC);
		if (fd < 0)
			return NULL;
		if (O_CLOEXEC == 0) /* ancient libc */
			close_on_exec_on(fd);
	}

	fp = xmalloc(sizeof(*fp));
	if (name == NULL)
		G.HFILE_stdin = fp;
	fp->fd = fd;
	fp->cur = fp->end = fp->buf;
	fp->next_hfile = G.HFILE_list;
	G.HFILE_list = fp;
	return fp;
}
static void hfclose(HFILE *fp)
{
	HFILE **pp = &G.HFILE_list;
	while (*pp) {
		HFILE *cur = *pp;
		if (cur == fp) {
			*pp = cur->next_hfile;
			break;
		}
		pp = &cur->next_hfile;
	}
	if (fp->fd >= 0)
		close(fp->fd);
	free(fp);
}
static int refill_HFILE_and_getc(HFILE *fp)
{
	int n;

	if (fp->fd < 0) {
		/* Already saw EOF */
		return EOF;
	}
	/* Try to buffer more input */
	fp->cur = fp->buf;
	n = safe_read(fp->fd, fp->buf, sizeof(fp->buf));
	if (n < 0) {
		bb_simple_perror_msg("read error");
		n = 0;
	}
	fp->end = fp->buf + n;
	if (n == 0) {
		/* EOF/error */
		close(fp->fd);
		fp->fd = -1;
		return EOF;
	}
	return (unsigned char)(*fp->cur++);
}
/* Inlined for common case of non-empty buffer.
 */
static ALWAYS_INLINE int hfgetc(HFILE *fp)
{
	if (fp->cur < fp->end)
		return (unsigned char)(*fp->cur++);
	/* Buffer empty */
	return refill_HFILE_and_getc(fp);
}
static int move_HFILEs_on_redirect(int fd, int avoid_fd)
{
	HFILE *fl = G.HFILE_list;
	while (fl) {
		if (fd == fl->fd) {
			/* We use it only on script files, they are all CLOEXEC */
			fl->fd = xdup_CLOEXEC_and_close(fd, avoid_fd);
			debug_printf_redir("redirect_fd %d: matches a script fd, moving it to %d\n", fd, fl->fd);
			return 1; /* "found and moved" */
		}
		fl = fl->next_hfile;
	}
#if ENABLE_HUSH_MODE_X
	if (G.x_mode_fd > 0 && fd == G.x_mode_fd) {
		G.x_mode_fd = xdup_CLOEXEC_and_close(fd, avoid_fd);
		return 1; /* "found and moved" */
	}
#endif
	return 0; /* "not in the list" */
}
#if ENABLE_FEATURE_SH_STANDALONE && BB_MMU
static void close_all_HFILE_list(void)
{
	HFILE *fl = G.HFILE_list;
	while (fl) {
		/* hfclose would also free HFILE object.
		 * It is disastrous if we share memory with a vforked parent.
		 * I'm not sure we never come here after vfork.
		 * Therefore just close fd, nothing more.
		 *
		 * ">" instead of ">=": we don't close fd#0,
		 * interactive shell uses hfopen(NULL) as stdin input
		 * which has fl->fd == 0, but fd#0 gets redirected in pipes.
		 * If we'd close it here, then e.g. interactive "set | sort"
		 * with NOFORKed sort, would have sort's input fd closed.
		 */
		if (fl->fd > 0)
			/*hfclose(fl); - unsafe */
			close(fl->fd);
		fl = fl->next_hfile;
	}
}
#endif
static int fd_in_HFILEs(int fd)
{
	HFILE *fl = G.HFILE_list;
	while (fl) {
		if (fl->fd == fd)
			return 1;
		fl = fl->next_hfile;
	}
	return 0;
}


/* Helpers for setting new $n and restoring them back
 */
typedef struct save_arg_t {
	char *sv_argv0;
	char **sv_g_argv;
	int sv_g_argc;
	IF_HUSH_SET(smallint sv_g_malloced;)
} save_arg_t;

static void save_and_replace_G_args(save_arg_t *sv, char **argv)
{
	sv->sv_argv0 = argv[0];
	sv->sv_g_argv = G.global_argv;
	sv->sv_g_argc = G.global_argc;
	IF_HUSH_SET(sv->sv_g_malloced = G.global_args_malloced;)

	argv[0] = G.global_argv[0]; /* retain $0 */
	G.global_argv = argv;
	IF_HUSH_SET(G.global_args_malloced = 0;)

	G.global_argc = 1 + string_array_len(argv + 1);
}

static void restore_G_args(save_arg_t *sv, char **argv)
{
#if ENABLE_HUSH_SET
	if (G.global_args_malloced) {
		/* someone ran "set -- arg1 arg2 ...", undo */
		char **pp = G.global_argv;
		while (*++pp) /* note: does not free $0 */
			free(*pp);
		free(G.global_argv);
	}
#endif
	argv[0] = sv->sv_argv0;
	G.global_argv = sv->sv_g_argv;
	G.global_argc = sv->sv_g_argc;
	IF_HUSH_SET(G.global_args_malloced = sv->sv_g_malloced;)
}


/* Basic theory of signal handling in shell
 * ========================================
 * This does not describe what hush does, rather, it is current understanding
 * what it _should_ do. If it doesn't, it's a bug.
 * http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap
 *
 * Signals are handled only after each pipe ("cmd | cmd | cmd" thing)
 * is finished or backgrounded. It is the same in interactive and
 * non-interactive shells, and is the same regardless of whether
 * a user trap handler is installed or a shell special one is in effect.
 * ^C or ^Z from keyboard seems to execute "at once" because it usually
 * backgrounds (i.e. stops) or kills all members of currently running
 * pipe.
 *
 * Wait builtin is interruptible by signals for which user trap is set
 * or by SIGINT in interactive shell.
 *
 * Trap handlers will execute even within trap handlers. (right?)
 *
 * User trap handlers are forgotten when subshell ("(cmd)") is entered,
 * except for handlers set to '' (empty string).
 *
 * If job control is off, backgrounded commands ("cmd &")
 * have SIGINT, SIGQUIT set to SIG_IGN.
 *
 * Commands which are run in command substitution ("`cmd`")
 * have SIGTTIN, SIGTTOU, SIGTSTP set to SIG_IGN.
 *
 * Ordinary commands have signals set to SIG_IGN/DFL as inherited
 * by the shell from its parent.
 *
 * Signals which differ from SIG_DFL action
 * (note: child (i.e., [v]forked) shell is not an interactive shell):
 *
 * SIGQUIT: ignore
 * SIGTERM (interactive): ignore
 * SIGHUP (interactive):
 *    send SIGCONT to stopped jobs, send SIGHUP to all jobs and exit
 * SIGTTIN, SIGTTOU, SIGTSTP (if job control is on): ignore
 *    Note that ^Z is handled not by trapping SIGTSTP, but by seeing
 *    that all pipe members are stopped. Try this in bash:
 *    while :; do :; done - ^Z does not background it
 *    (while :; do :; done) - ^Z backgrounds it
 * SIGINT (interactive): wait for last pipe, ignore the rest
 *    of the command line, show prompt. NB: ^C does not send SIGINT
 *    to interactive shell while shell is waiting for a pipe,
 *    since shell is bg'ed (is not in foreground process group).
 *    Example 1: this waits 5 sec, but does not execute ls:
 *    "echo $$; sleep 5; ls -l" + "kill -INT <pid>"
 *    Example 2: this does not wait and does not execute ls:
 *    "echo $$; sleep 5 & wait; ls -l" + "kill -INT <pid>"
 *    Example 3: this does not wait 5 sec, but executes ls:
 *    "sleep 5; ls -l" + press ^C
 *    Example 4: this does not wait and does not execute ls:
 *    "sleep 5 & wait; ls -l" + press ^C
 *
 * (What happens to signals which are IGN on shell start?)
 * (What happens with signal mask on shell start?)
 *
 * Old implementation
 * ==================
 * We use in-kernel pending signal mask to determine which signals were sent.
 * We block all signals which we don't want to take action immediately,
 * i.e. we block all signals which need to have special handling as described
 * above, and all signals which have traps set.
 * After each pipe execution, we extract any pending signals via sigtimedwait()
 * and act on them.
 *
 * unsigned special_sig_mask: a mask of such "special" signals
 * sigset_t blocked_set:  current blocked signal set
 *
 * "trap - SIGxxx":
 *    clear bit in blocked_set unless it is also in special_sig_mask
 * "trap 'cmd' SIGxxx":
 *    set bit in blocked_set (even if 'cmd' is '')
 * after [v]fork, if we plan to be a shell:
 *    unblock signals with special interactive handling
 *    (child shell is not interactive),
 *    unset all traps except '' (note: regardless of child shell's type - {}, (), etc)
 * after [v]fork, if we plan to exec:
 *    POSIX says fork clears pending signal mask in child - no need to clear it.
 *    Restore blocked signal set to one inherited by shell just prior to exec.
 *
 * Note: as a result, we do not use signal handlers much. The only uses
 * are to count SIGCHLDs
 * and to restore tty pgrp on signal-induced exit.
 *
 * Note 2 (compat):
 * Standard says "When a subshell is entered, traps that are not being ignored
 * are set to the default actions". bash interprets it so that traps which
 * are set to '' (ignore) are NOT reset to defaults. We do the same.
 *
 * Problem: the above approach makes it unwieldy to catch signals while
 * we are in read builtin, or while we read commands from stdin:
 * masked signals are not visible!
 *
 * New implementation
 * ==================
 * We record each signal we are interested in by installing signal handler
 * for them - a bit like emulating kernel pending signal mask in userspace.
 * We are interested in: signals which need to have special handling
 * as described above, and all signals which have traps set.
 * Signals are recorded in pending_set.
 * After each pipe execution, we extract any pending signals
 * and act on them.
 *
 * unsigned special_sig_mask: a mask of shell-special signals.
 * unsigned fatal_sig_mask: a mask of signals on which we restore tty pgrp.
 * char *traps[sig] if trap for sig is set (even if it's '').
 * sigset_t pending_set: set of sigs we received.
 *
 * "trap - SIGxxx":
 *    if sig is in special_sig_mask, set handler back to:
 *        record_pending_signo, or to IGN if it's a tty stop signal
 *    if sig is in fatal_sig_mask, set handler back to sigexit.
 *    else: set handler back to SIG_DFL
 * "trap 'cmd' SIGxxx":
 *    set handler to record_pending_signo.
 * "trap '' SIGxxx":
 *    set handler to SIG_IGN.
 * after [v]fork, if we plan to be a shell:
 *    set signals with special interactive handling to SIG_DFL
 *    (because child shell is not interactive),
 *    unset all traps except '' (note: regardless of child shell's type - {}, (), etc)
 * after [v]fork, if we plan to exec:
 *    POSIX says fork clears pending signal mask in child - no need to clear it.
 *
 * To make wait builtin interruptible, we handle SIGCHLD as special signal,
 * otherwise (if we leave it SIG_DFL) sigsuspend in wait builtin will not wake up on it.
 *
 * Note (compat):
 * Standard says "When a subshell is entered, traps that are not being ignored
 * are set to the default actions". bash interprets it so that traps which
 * are set to '' (ignore) are NOT reset to defaults. We do the same.
 */
enum {
	SPECIAL_INTERACTIVE_SIGS = 0
		| (1 << SIGTERM)
		| (1 << SIGINT)
		| (1 << SIGHUP)
		,
	SPECIAL_JOBSTOP_SIGS = 0
#if ENABLE_HUSH_JOB
		| (1 << SIGTTIN)
		| (1 << SIGTTOU)
		| (1 << SIGTSTP)
#endif
		,
};

static void record_pending_signo(int sig)
{
	sigaddset(&G.pending_set, sig);
#if ENABLE_HUSH_FAST
	if (sig == SIGCHLD) {
		G.count_SIGCHLD++;
//bb_error_msg("[%d] SIGCHLD_handler: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
	}
#endif
}

static sighandler_t install_sighandler(int sig, sighandler_t handler)
{
	struct sigaction old_sa;

	/* We could use signal() to install handlers... almost:
	 * except that we need to mask ALL signals while handlers run.
	 * I saw signal nesting in strace, race window isn't small.
	 * SA_RESTART is also needed, but in Linux, signal()
	 * sets SA_RESTART too.
	 */
	/* memset(&G.sa, 0, sizeof(G.sa)); - already done */
	/* sigfillset(&G.sa.sa_mask);      - already done */
	/* G.sa.sa_flags = SA_RESTART;     - already done */
	G.sa.sa_handler = handler;
	sigaction(sig, &G.sa, &old_sa);
	return old_sa.sa_handler;
}

static void hush_exit(int exitcode) NORETURN;

static void restore_ttypgrp_and__exit(void) NORETURN;
static void restore_ttypgrp_and__exit(void)
{
	/* xfunc has failed! die die die */
	/* no EXIT traps, this is an escape hatch! */
	G.exiting = 1;
	hush_exit(xfunc_error_retval);
}

#if ENABLE_HUSH_JOB

/* Needed only on some libc:
 * It was observed that on exit(), fgetc'ed buffered data
 * gets "unwound" via lseek(fd, -NUM, SEEK_CUR).
 * With the net effect that even after fork(), not vfork(),
 * exit() in NOEXECed applet in "sh SCRIPT":
 *	noexec_applet_here
 *	echo END_OF_SCRIPT
 * lseeks fd in input FILE object from EOF to "e" in "echo END_OF_SCRIPT".
 * This makes "echo END_OF_SCRIPT" executed twice.
 * Similar problems can be seen with msg_and_die_if_script() -> xfunc_die()
 * and in `cmd` handling.
 * If set as die_func(), this makes xfunc_die() exit via _exit(), not exit():
 */
static void fflush_and__exit(void) NORETURN;
static void fflush_and__exit(void)
{
	fflush_all();
	_exit(xfunc_error_retval);
}

/* After [v]fork, in child: do not restore tty pgrp on xfunc death */
# define disable_restore_tty_pgrp_on_exit() (die_func = fflush_and__exit)
/* After [v]fork, in parent: restore tty pgrp on xfunc death */
# define enable_restore_tty_pgrp_on_exit()  (die_func = restore_ttypgrp_and__exit)

/* Restores tty foreground process group, and exits.
 * May be called as signal handler for fatal signal
 * (will resend signal to itself, producing correct exit state)
 * or called directly with -EXITCODE.
 * We also call it if xfunc is exiting.
 */
static void sigexit(int sig) NORETURN;
static void sigexit(int sig)
{
	/* Careful: we can end up here after [v]fork. Do not restore
	 * tty pgrp then, only top-level shell process does that */
	if (G_saved_tty_pgrp && getpid() == G.root_pid) {
		/* Disable all signals: job control, SIGPIPE, etc.
		 * Mostly paranoid measure, to prevent infinite SIGTTOU.
		 */
		sigprocmask_allsigs(SIG_BLOCK);
		tcsetpgrp(G_interactive_fd, G_saved_tty_pgrp);
	}

	/* Not a signal, just exit */
	if (sig <= 0)
		_exit(- sig);

	kill_myself_with_sig(sig); /* does not return */
}
#else

# define disable_restore_tty_pgrp_on_exit() ((void)0)
# define enable_restore_tty_pgrp_on_exit()  ((void)0)

#endif

static sighandler_t pick_sighandler(unsigned sig)
{
	sighandler_t handler = SIG_DFL;
	if (sig < sizeof(unsigned)*8) {
		unsigned sigmask = (1 << sig);

#if ENABLE_HUSH_JOB
		/* is sig fatal? */
		if (G_fatal_sig_mask & sigmask)
			handler = sigexit;
		else
#endif
		/* sig has special handling? */
		if (G.special_sig_mask & sigmask) {
			handler = record_pending_signo;
			/* TTIN/TTOU/TSTP can't be set to record_pending_signo
			 * in order to ignore them: they will be raised
			 * in an endless loop when we try to do some
			 * terminal ioctls! We do have to _ignore_ these.
			 */
			if (SPECIAL_JOBSTOP_SIGS & sigmask)
				handler = SIG_IGN;
		}
	}
	return handler;
}

/* Restores tty foreground process group, and exits. */
static void hush_exit(int exitcode)
{
#if ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
	if (G.line_input_state)
		save_history(G.line_input_state);
#endif

	fflush_all();
	if (G.exiting <= 0 && G_traps && G_traps[0] && G_traps[0][0]) {
		char *argv[3];
		/* argv[0] is unused */
		argv[1] = xstrdup(G_traps[0]); /* copy, since EXIT trap handler may modify G_traps[0] */
		argv[2] = NULL;
		G.exiting = 1; /* prevent EXIT trap recursion */
		/* Note: G_traps[0] is not cleared!
		 * "trap" will still show it, if executed
		 * in the handler */
		builtin_eval(argv);
	}

#if ENABLE_FEATURE_CLEAN_UP
	{
		struct variable *cur_var;
		if (G.cwd != bb_msg_unknown)
			free((char*)G.cwd);
		cur_var = G.top_var;
		while (cur_var) {
			struct variable *tmp = cur_var;
			if (!cur_var->max_len)
				free(cur_var->varstr);
			cur_var = cur_var->next;
			free(tmp);
		}
	}
#endif

	fflush_all();
#if ENABLE_HUSH_JOB
	sigexit(- (exitcode & 0xff));
#else
	_exit(exitcode);
#endif
}


//TODO: return a mask of ALL handled sigs?
static int check_and_run_traps(void)
{
	int last_sig = 0;

	while (1) {
		int sig;

		if (sigisemptyset(&G.pending_set))
			break;
		sig = 0;
		do {
			sig++;
			if (sigismember(&G.pending_set, sig)) {
				sigdelset(&G.pending_set, sig);
				goto got_sig;
			}
		} while (sig < NSIG);
		break;
 got_sig:
#if ENABLE_HUSH_TRAP
		if (G_traps && G_traps[sig]) {
			debug_printf_exec("%s: sig:%d handler:'%s'\n", __func__, sig, G.traps[sig]);
			if (G_traps[sig][0]) {
				/* We have user-defined handler */
				smalluint save_rcode;
				int save_pre;
				char *argv[3];
				/* argv[0] is unused */
				argv[1] = xstrdup(G_traps[sig]);
				/* why strdup? trap can modify itself: trap 'trap "echo oops" INT' INT */
				argv[2] = NULL;
				save_pre = G.pre_trap_exitcode;
				G.pre_trap_exitcode = save_rcode = G.last_exitcode;
				builtin_eval(argv);
				free(argv[1]);
				G.pre_trap_exitcode = save_pre;
				G.last_exitcode = save_rcode;
# if ENABLE_HUSH_FUNCTIONS
				if (G.return_exitcode >= 0) {
					debug_printf_exec("trap exitcode:%d\n", G.return_exitcode);
					G.last_exitcode = G.return_exitcode;
				}
# endif
				last_sig = sig;
			} /* else: "" trap, ignoring signal */
			continue;
		}
#endif
		/* not a trap: special action */
		switch (sig) {
		case SIGINT:
			debug_printf_exec("%s: sig:%d default SIGINT handler\n", __func__, sig);
			G.flag_SIGINT = 1;
			last_sig = sig;
			break;
#if ENABLE_HUSH_JOB
		case SIGHUP: {
//TODO: why are we doing this? ash and dash don't do this,
//they have no handler for SIGHUP at all,
//they rely on kernel to send SIGHUP+SIGCONT to orphaned process groups
			struct pipe *job;
			debug_printf_exec("%s: sig:%d default SIGHUP handler\n", __func__, sig);
			/* bash is observed to signal whole process groups,
			 * not individual processes */
			for (job = G.job_list; job; job = job->next) {
				if (job->pgrp <= 0)
					continue;
				debug_printf_exec("HUPing pgrp %d\n", job->pgrp);
				if (kill(- job->pgrp, SIGHUP) == 0)
					kill(- job->pgrp, SIGCONT);
			}
			sigexit(SIGHUP);
		}
#endif
#if ENABLE_HUSH_FAST
		case SIGCHLD:
			debug_printf_exec("%s: sig:%d default SIGCHLD handler\n", __func__, sig);
			G.count_SIGCHLD++;
//bb_error_msg("[%d] check_and_run_traps: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
			/* Note:
			 * We don't do 'last_sig = sig' here -> NOT returning this sig.
			 * This simplifies wait builtin a bit.
			 */
			break;
#endif
		default: /* ignored: */
			debug_printf_exec("%s: sig:%d default handling is to ignore\n", __func__, sig);
			/* SIGTERM, SIGQUIT, SIGTTIN, SIGTTOU, SIGTSTP */
			/* Note:
			 * We don't do 'last_sig = sig' here -> NOT returning this sig.
			 * Example: wait is not interrupted by TERM
			 * in interactive shell, because TERM is ignored.
			 */
			break;
		}
	}
	return last_sig;
}


static const char *get_cwd(int force)
{
	if (force || G.cwd == NULL) {
		/* xrealloc_getcwd_or_warn(arg) calls free(arg),
		 * we must not try to free(bb_msg_unknown) */
		if (G.cwd == bb_msg_unknown)
			G.cwd = NULL;
		G.cwd = xrealloc_getcwd_or_warn((char *)G.cwd);
		if (!G.cwd)
			G.cwd = bb_msg_unknown;
	}
	return G.cwd;
}


/*
 * Shell and environment variable support
 */
static struct variable **get_ptr_to_local_var(const char *name, unsigned len)
{
	struct variable **pp;
	struct variable *cur;

	pp = &G.top_var;
	while ((cur = *pp) != NULL) {
		if (strncmp(cur->varstr, name, len) == 0 && cur->varstr[len] == '=')
			return pp;
		pp = &cur->next;
	}
	return NULL;
}

static const char* FAST_FUNC get_local_var_value(const char *name)
{
	struct variable **vpp;
	unsigned len = strlen(name);

	if (G.expanded_assignments) {
		char **cpp = G.expanded_assignments;
		while (*cpp) {
			char *cp = *cpp;
			if (strncmp(cp, name, len) == 0 && cp[len] == '=')
				return cp + len + 1;
			cpp++;
		}
	}

	vpp = get_ptr_to_local_var(name, len);
	if (vpp)
		return (*vpp)->varstr + len + 1;

	if (strcmp(name, "PPID") == 0)
		return utoa(G.root_ppid);
	// bash compat: UID? EUID?
#if ENABLE_HUSH_RANDOM_SUPPORT
	if (strcmp(name, "RANDOM") == 0)
		return utoa(next_random(&G.random_gen));
#endif
#if ENABLE_HUSH_LINENO_VAR
	if (strcmp(name, "LINENO") == 0)
		return utoa(G.execute_lineno);
#endif
#if BASH_EPOCH_VARS
	{
		const char *fmt = NULL;
		if (strcmp(name, "EPOCHSECONDS") == 0)
			fmt = "%lu";
		else if (strcmp(name, "EPOCHREALTIME") == 0)
			fmt = "%lu.%06u";
		if (fmt) {
			struct timeval tv;
			gettimeofday(&tv, NULL);
			sprintf(G.epoch_buf, fmt, (unsigned long)tv.tv_sec,
					(unsigned)tv.tv_usec);
			return G.epoch_buf;
		}
	}
#endif
	return NULL;
}

#if ENABLE_HUSH_GETOPTS
static void handle_changed_special_names(const char *name, unsigned name_len)
{
	if (name_len == 6) {
		if (strncmp(name, "OPTIND", 6) == 0) {
			G.getopt_count = 0;
			return;
		}
	}
}
#else
/* Do not even bother evaluating arguments */
# define handle_changed_special_names(...) ((void)0)
#endif

/* str holds "NAME=VAL" and is expected to be malloced.
 * We take ownership of it.
 */
#define SETFLAG_EXPORT   (1 << 0)
#define SETFLAG_UNEXPORT (1 << 1)
#define SETFLAG_MAKE_RO  (1 << 2)
#define SETFLAG_VARLVL_SHIFT   3
static int set_local_var(char *str, unsigned flags)
{
	struct variable **cur_pp;
	struct variable *cur;
	char *free_me = NULL;
	char *eq_sign;
	int name_len;
	int retval;
	unsigned local_lvl = (flags >> SETFLAG_VARLVL_SHIFT);

	eq_sign = strchr(str, '=');
	if (HUSH_DEBUG && !eq_sign)
		bb_simple_error_msg_and_die("BUG in setvar");

	name_len = eq_sign - str + 1; /* including '=' */
	cur_pp = &G.top_var;
	while ((cur = *cur_pp) != NULL) {
		if (strncmp(cur->varstr, str, name_len) != 0) {
			cur_pp = &cur->next;
			continue;
		}

		/* We found an existing var with this name */
		if (cur->flg_read_only) {
			bb_error_msg("%s: readonly variable", str);
			free(str);
//NOTE: in bash, assignment in "export READONLY_VAR=Z" fails, and sets $?=1,
//but export per se succeeds (does put the var in env). We don't mimic that.
			return -1;
		}
		if (flags & SETFLAG_UNEXPORT) { // && cur->flg_export ?
			debug_printf_env("%s: unsetenv '%s'\n", __func__, str);
			*eq_sign = '\0';
			unsetenv(str);
			*eq_sign = '=';
		}
		if (cur->var_nest_level < local_lvl) {
			/* bash 3.2.33(1) and exported vars:
			 * # export z=z
			 * # f() { local z=a; env | grep ^z; }
			 * # f
			 * z=a
			 * # env | grep ^z
			 * z=z
			 */
			if (cur->flg_export)
				flags |= SETFLAG_EXPORT;
			/* New variable is local ("local VAR=VAL" or
			 * "VAR=VAL cmd")
			 * and existing one is global, or local
			 * on a lower level that new one.
			 * Remove it from global variable list:
			 */
			*cur_pp = cur->next;
			if (G.shadowed_vars_pp) {
				/* Save in "shadowed" list */
				debug_printf_env("shadowing %s'%s'/%u by '%s'/%u\n",
					cur->flg_export ? "exported " : "",
					cur->varstr, cur->var_nest_level, str, local_lvl
				);
				cur->next = *G.shadowed_vars_pp;
				*G.shadowed_vars_pp = cur;
			} else {
				/* Came from pseudo_exec_argv(), no need to save: delete it */
				debug_printf_env("shadow-deleting %s'%s'/%u by '%s'/%u\n",
					cur->flg_export ? "exported " : "",
					cur->varstr, cur->var_nest_level, str, local_lvl
				);
				if (cur->max_len == 0) /* allocated "VAR=VAL"? */
					free_me = cur->varstr; /* then free it later */
				free(cur);
			}
			break;
		}

		if (strcmp(cur->varstr + name_len, eq_sign + 1) == 0) {
			debug_printf_env("assignement '%s' does not change anything\n", str);
 free_and_exp:
			free(str);
			goto exp;
		}

		/* Replace the value in the found "struct variable" */
		if (cur->max_len != 0) {
			if (cur->max_len >= strnlen(str, cur->max_len + 1)) {
				/* This one is from startup env, reuse space */
				debug_printf_env("reusing startup env for '%s'\n", str);
				strcpy(cur->varstr, str);
				goto free_and_exp;
			}
			/* Can't reuse */
			cur->max_len = 0;
			goto set_str_and_exp;
		}
		/* max_len == 0 signifies "malloced" var, which we can
		 * (and have to) free. But we can't free(cur->varstr) here:
		 * if cur->flg_export is 1, it is in the environment.
		 * We should either unsetenv+free, or wait until putenv,
		 * then putenv(new)+free(old).
		 */
		free_me = cur->varstr;
		goto set_str_and_exp;
	}

	/* Not found or shadowed - create new variable struct */
	debug_printf_env("%s: alloc new var '%s'/%u\n", __func__, str, local_lvl);
	cur = xzalloc(sizeof(*cur));
	cur->var_nest_level = local_lvl;
	cur->next = *cur_pp;
	*cur_pp = cur;

 set_str_and_exp:
	cur->varstr = str;
 exp:
#if !BB_MMU || ENABLE_HUSH_READONLY
	if (flags & SETFLAG_MAKE_RO) {
		cur->flg_read_only = 1;
	}
#endif
	if (flags & SETFLAG_EXPORT)
		cur->flg_export = 1;
	retval = 0;
	if (cur->flg_export) {
		if (flags & SETFLAG_UNEXPORT) {
			cur->flg_export = 0;
			/* unsetenv was already done */
		} else {
			debug_printf_env("%s: putenv '%s'/%u\n", __func__, cur->varstr, cur->var_nest_level);
			retval = putenv(cur->varstr);
			/* fall through to "free(free_me)" -
			 * only now we can free old exported malloced string
			 */
		}
	}
	free(free_me);

	handle_changed_special_names(cur->varstr, name_len - 1);

	return retval;
}

static void FAST_FUNC set_local_var_from_halves(const char *name, const char *val)
{
	char *var = xasprintf("%s=%s", name, val);
	set_local_var(var, /*flag:*/ 0);
}

/* Used at startup and after each cd */
static void set_pwd_var(unsigned flag)
{
	set_local_var(xasprintf("PWD=%s", get_cwd(/*force:*/ 1)), flag);
}

#if ENABLE_HUSH_UNSET || ENABLE_HUSH_GETOPTS
static int unset_local_var_len(const char *name, int name_len)
{
	struct variable *cur;
	struct variable **cur_pp;

	cur_pp = &G.top_var;
	while ((cur = *cur_pp) != NULL) {
		if (strncmp(cur->varstr, name, name_len) == 0
		 && cur->varstr[name_len] == '='
		) {
			if (cur->flg_read_only) {
				bb_error_msg("%s: readonly variable", name);
				return EXIT_FAILURE;
			}

			*cur_pp = cur->next;
			debug_printf_env("%s: unsetenv '%s'\n", __func__, cur->varstr);
			bb_unsetenv(cur->varstr);
			if (!cur->max_len)
				free(cur->varstr);
			free(cur);

			break;
		}
		cur_pp = &cur->next;
	}

	/* Handle "unset LINENO" et al even if did not find the variable to unset */
	handle_changed_special_names(name, name_len);

	return EXIT_SUCCESS;
}

static int unset_local_var(const char *name)
{
	return unset_local_var_len(name, strlen(name));
}
#endif


/*
 * Helpers for "var1=val1 var2=val2 cmd" feature
 */
static void add_vars(struct variable *var)
{
	struct variable *next;

	while (var) {
		next = var->next;
		var->next = G.top_var;
		G.top_var = var;
		if (var->flg_export) {
			debug_printf_env("%s: restoring exported '%s'/%u\n", __func__, var->varstr, var->var_nest_level);
			putenv(var->varstr);
		} else {
			debug_printf_env("%s: restoring variable '%s'/%u\n", __func__, var->varstr, var->var_nest_level);
		}
		var = next;
	}
}

/* We put strings[i] into variable table and possibly putenv them.
 * If variable is read only, we can free the strings[i]
 * which attempts to overwrite it.
 * The strings[] vector itself is freed.
 */
static void set_vars_and_save_old(char **strings)
{
	char **s;

	if (!strings)
		return;

	s = strings;
	while (*s) {
		struct variable *var_p;
		struct variable **var_pp;
		char *eq;

		eq = strchr(*s, '=');
		if (HUSH_DEBUG && !eq)
			bb_simple_error_msg_and_die("BUG in varexp4");
		var_pp = get_ptr_to_local_var(*s, eq - *s);
		if (var_pp) {
			var_p = *var_pp;
			if (var_p->flg_read_only) {
				char **p;
				bb_error_msg("%s: readonly variable", *s);
				/*
				 * "VAR=V BLTIN" unsets VARs after BLTIN completes.
				 * If VAR is readonly, leaving it in the list
				 * after asssignment error (msg above)
				 * causes doubled error message later, on unset.
				 */
				debug_printf_env("removing/freeing '%s' element\n", *s);
				free(*s);
				p = s;
				do { *p = p[1]; p++; } while (*p);
				goto next;
			}
			/* below, set_local_var() with nest level will
			 * "shadow" (remove) this variable from
			 * global linked list.
			 */
		}
		debug_printf_env("%s: env override '%s'/%u\n", __func__, *s, G.var_nest_level);
		set_local_var(*s, (G.var_nest_level << SETFLAG_VARLVL_SHIFT) | SETFLAG_EXPORT);
		s++;
 next: ;
	}
	free(strings);
}


/*
 * Unicode helper
 */
static void reinit_unicode_for_hush(void)
{
	/* Unicode support should be activated even if LANG is set
	 * _during_ shell execution, not only if it was set when
	 * shell was started. Therefore, re-check LANG every time:
	 */
	if (ENABLE_FEATURE_CHECK_UNICODE_IN_ENV
	 || ENABLE_UNICODE_USING_LOCALE
	) {
		const char *s = get_local_var_value("LC_ALL");
		if (!s) s = get_local_var_value("LC_CTYPE");
		if (!s) s = get_local_var_value("LANG");
		reinit_unicode(s);
	}
}

/*
 * in_str support (strings, and "strings" read from files).
 */

#if ENABLE_HUSH_INTERACTIVE
/* To test correct lineedit/interactive behavior, type from command line:
 *	echo $P\
 *	\
 *	AT\
 *	H\
 *	\
 * It exercises a lot of corner cases.
 */
static const char *setup_prompt_string(void)
{
	const char *prompt_str;

	debug_printf_prompt("%s promptmode:%d\n", __func__, G.promptmode);

# if ENABLE_FEATURE_EDITING_FANCY_PROMPT
	prompt_str = get_local_var_value(G.promptmode == 0 ? "PS1" : "PS2");
	if (!prompt_str)
		prompt_str = "";
# else
	prompt_str = "> "; /* if PS2, else... */
	if (G.promptmode == 0) { /* PS1 */
		/* No fancy prompts supported, (re)generate "CURDIR $ " by hand */
		free(G.PS1);
		/* bash uses $PWD value, even if it is set by user.
		 * It uses current dir only if PWD is unset.
		 * We always use current dir. */
		G.PS1 = xasprintf("%s %c ", get_cwd(0), (geteuid() != 0) ? '$' : '#');
	}
# endif
	debug_printf("prompt_str '%s'\n", prompt_str);
	return prompt_str;
}
static int get_user_input(struct in_str *i)
{
	int r;
	const char *prompt_str;

	prompt_str = setup_prompt_string();
# if ENABLE_FEATURE_EDITING
	for (;;) {
		reinit_unicode_for_hush();
		if (G.flag_SIGINT) {
			/* There was ^C'ed, make it look prettier: */
			bb_putchar('\n');
			G.flag_SIGINT = 0;
		}
		/* buglet: SIGINT will not make new prompt to appear _at once_,
		 * only after <Enter>. (^C works immediately) */
		r = read_line_input(G.line_input_state, prompt_str,
				G.user_input_buf, CONFIG_FEATURE_EDITING_MAX_LEN-1
		);
		/* read_line_input intercepts ^C, "convert" it to SIGINT */
		if (r == 0)
			raise(SIGINT);
		check_and_run_traps();
		if (r != 0 && !G.flag_SIGINT)
			break;
		/* ^C or SIGINT: repeat */
		/* bash prints ^C even on real SIGINT (non-kbd generated) */
		write(STDOUT_FILENO, "^C", 2);
		G.last_exitcode = 128 + SIGINT;
	}
	if (r < 0) {
		/* EOF/error detected */
		i->p = NULL;
		i->peek_buf[0] = r = EOF;
		return r;
	}
	i->p = G.user_input_buf;
	return (unsigned char)*i->p++;
# else
	for (;;) {
		G.flag_SIGINT = 0;
		if (i->last_char == '\0' || i->last_char == '\n') {
			/* Why check_and_run_traps here? Try this interactively:
			 * $ trap 'echo INT' INT; (sleep 2; kill -INT $$) &
			 * $ <[enter], repeatedly...>
			 * Without check_and_run_traps, handler never runs.
			 */
			check_and_run_traps();
			fputs(prompt_str, stdout);
		}
		fflush_all();
//FIXME: here ^C or SIGINT will have effect only after <Enter>
		r = hfgetc(i->file);
		/* In !ENABLE_FEATURE_EDITING we don't use read_line_input,
		 * no ^C masking happens during fgetc, no special code for ^C:
		 * it generates SIGINT as usual.
		 */
		check_and_run_traps();
		if (G.flag_SIGINT)
			G.last_exitcode = 128 + SIGINT;
		if (r != '\0')
			break;
	}
	return r;
# endif
}
/* This is the magic location that prints prompts
 * and gets data back from the user */
static int fgetc_interactive(struct in_str *i)
{
	int ch;
	/* If it's interactive stdin, get new line. */
	if (G_interactive_fd && i->file == G.HFILE_stdin) {
		/* Returns first char (or EOF), the rest is in i->p[] */
		ch = get_user_input(i);
		G.promptmode = 1; /* PS2 */
		debug_printf_prompt("%s promptmode=%d\n", __func__, G.promptmode);
	} else {
		/* Not stdin: script file, sourced file, etc */
		do ch = hfgetc(i->file); while (ch == '\0');
	}
	return ch;
}
#else
static ALWAYS_INLINE int fgetc_interactive(struct in_str *i)
{
	int ch;
	do ch = hfgetc(i->file); while (ch == '\0');
	return ch;
}
#endif  /* INTERACTIVE */

static int i_getch(struct in_str *i)
{
	int ch;

	if (!i->file) {
		/* string-based in_str */
		ch = (unsigned char)*i->p;
		if (ch != '\0') {
			i->p++;
			i->last_char = ch;
			return ch;
		}
		return EOF;
	}

	/* FILE-based in_str */

#if ENABLE_FEATURE_EDITING
	/* This can be stdin, check line editing char[] buffer */
	if (i->p && *i->p != '\0') {
		ch = (unsigned char)*i->p++;
		goto out;
	}
#endif
	/* peek_buf[] is an int array, not char. Can contain EOF. */
	ch = i->peek_buf[0];
	if (ch != 0) {
		int ch2 = i->peek_buf[1];
		i->peek_buf[0] = ch2;
		if (ch2 == 0) /* very likely, avoid redundant write */
			goto out;
		i->peek_buf[1] = 0;
		goto out;
	}

	ch = fgetc_interactive(i);
 out:
	debug_printf("file_get: got '%c' %d\n", ch, ch);
	i->last_char = ch;
#if ENABLE_HUSH_LINENO_VAR
	if (ch == '\n') {
		G.parse_lineno++;
		debug_printf_parse("G.parse_lineno++ = %u\n", G.parse_lineno);
	}
#endif
	return ch;
}

static int i_peek(struct in_str *i)
{
	int ch;

	if (!i->file) {
		/* string-based in_str */
		/* Doesn't report EOF on NUL. None of the callers care. */
		return (unsigned char)*i->p;
	}

	/* FILE-based in_str */

#if ENABLE_FEATURE_EDITING && ENABLE_HUSH_INTERACTIVE
	/* This can be stdin, check line editing char[] buffer */
	if (i->p && *i->p != '\0')
		return (unsigned char)*i->p;
#endif
	/* peek_buf[] is an int array, not char. Can contain EOF. */
	ch = i->peek_buf[0];
	if (ch != 0)
		return ch;

	/* Need to get a new char */
	ch = fgetc_interactive(i);
	debug_printf("file_peek: got '%c' %d\n", ch, ch);

	/* Save it by either rolling back line editing buffer, or in i->peek_buf[0] */
#if ENABLE_FEATURE_EDITING && ENABLE_HUSH_INTERACTIVE
	if (i->p) {
		i->p -= 1;
		return ch;
	}
#endif
	i->peek_buf[0] = ch;
	/*i->peek_buf[1] = 0; - already is */
	return ch;
}

/* Only ever called if i_peek() was called, and did not return EOF.
 * IOW: we know the previous peek saw an ordinary char, not EOF, not NUL,
 * not end-of-line. Therefore we never need to read a new editing line here.
 */
static int i_peek2(struct in_str *i)
{
	int ch;

	/* There are two cases when i->p[] buffer exists.
	 * (1) it's a string in_str.
	 * (2) It's a file, and we have a saved line editing buffer.
	 * In both cases, we know that i->p[0] exists and not NUL, and
	 * the peek2 result is in i->p[1].
	 */
	if (i->p)
		return (unsigned char)i->p[1];

	/* Now we know it is a file-based in_str. */

	/* peek_buf[] is an int array, not char. Can contain EOF. */
	/* Is there 2nd char? */
	ch = i->peek_buf[1];
	if (ch == 0) {
		/* We did not read it yet, get it now */
		do ch = hfgetc(i->file); while (ch == '\0');
		i->peek_buf[1] = ch;
	}

	debug_printf("file_peek2: got '%c' %d\n", ch, ch);
	return ch;
}

static int i_getch_and_eat_bkslash_nl(struct in_str *input)
{
	for (;;) {
		int ch, ch2;

		ch = i_getch(input);
		if (ch != '\\')
			return ch;
		ch2 = i_peek(input);
		if (ch2 != '\n')
			return ch;
		/* backslash+newline, skip it */
		i_getch(input);
	}
}

/* Note: this function _eats_ \<newline> pairs, safe to use plain
 * i_getch() after it instead of i_getch_and_eat_bkslash_nl().
 */
static int i_peek_and_eat_bkslash_nl(struct in_str *input)
{
	for (;;) {
		int ch, ch2;

		ch = i_peek(input);
		if (ch != '\\')
			return ch;
		ch2 = i_peek2(input);
		if (ch2 != '\n')
			return ch;
		/* backslash+newline, skip it */
		i_getch(input);
		i_getch(input);
	}
}

static void setup_file_in_str(struct in_str *i, HFILE *fp)
{
	memset(i, 0, sizeof(*i));
	i->file = fp;
	/* i->p = NULL; */
}

static void setup_string_in_str(struct in_str *i, const char *s)
{
	memset(i, 0, sizeof(*i));
	/*i->file = NULL */;
	i->p = s;
}


/*
 * o_string support
 */
#define B_CHUNK  (32 * sizeof(char*))

static void o_reset_to_empty_unquoted(o_string *o)
{
	o->length = 0;
	o->has_quoted_part = 0;
	if (o->data)
		o->data[0] = '\0';
}

static void o_free_and_set_NULL(o_string *o)
{
	free(o->data);
	memset(o, 0, sizeof(*o));
}

static ALWAYS_INLINE void o_free(o_string *o)
{
	free(o->data);
}

static void o_grow_by(o_string *o, int len)
{
	if (o->length + len > o->maxlen) {
		o->maxlen += (2 * len) | (B_CHUNK-1);
		o->data = xrealloc(o->data, 1 + o->maxlen);
	}
}

static void o_addchr(o_string *o, int ch)
{
	debug_printf("o_addchr: '%c' o->length=%d o=%p\n", ch, o->length, o);
	if (o->length < o->maxlen) {
		/* likely. avoid o_grow_by() call */
 add:
		o->data[o->length] = ch;
		o->length++;
		o->data[o->length] = '\0';
		return;
	}
	o_grow_by(o, 1);
	goto add;
}

#if 0
/* Valid only if we know o_string is not empty */
static void o_delchr(o_string *o)
{
	o->length--;
	o->data[o->length] = '\0';
}
#endif

static void o_addblock(o_string *o, const char *str, int len)
{
	o_grow_by(o, len);
	((char*)mempcpy(&o->data[o->length], str, len))[0] = '\0';
	o->length += len;
}

static void o_addstr(o_string *o, const char *str)
{
	o_addblock(o, str, strlen(str));
}

static void o_addstr_with_NUL(o_string *o, const char *str)
{
	o_addblock(o, str, strlen(str) + 1);
}

#if !BB_MMU
static void nommu_addchr(o_string *o, int ch)
{
	if (o)
		o_addchr(o, ch);
}
#else
# define nommu_addchr(o, str) ((void)0)
#endif

#if ENABLE_HUSH_MODE_X
static void x_mode_addchr(int ch)
{
	o_addchr(&G.x_mode_buf, ch);
}
static void x_mode_addstr(const char *str)
{
	o_addstr(&G.x_mode_buf, str);
}
static void x_mode_addblock(const char *str, int len)
{
	o_addblock(&G.x_mode_buf, str, len);
}
static void x_mode_prefix(void)
{
	int n = G.x_mode_depth;
	do x_mode_addchr('+'); while (--n >= 0);
}
static void x_mode_flush(void)
{
	int len = G.x_mode_buf.length;
	if (len <= 0)
		return;
	if (G.x_mode_fd > 0) {
		G.x_mode_buf.data[len] = '\n';
		full_write(G.x_mode_fd, G.x_mode_buf.data, len + 1);
	}
	G.x_mode_buf.length = 0;
}
#endif

/*
 * HUSH_BRACE_EXPANSION code needs corresponding quoting on variable expansion side.
 * Currently, "v='{q,w}'; echo $v" erroneously expands braces in $v.
 * Apparently, on unquoted $v bash still does globbing
 * ("v='*.txt'; echo $v" prints all .txt files),
 * but NOT brace expansion! Thus, there should be TWO independent
 * quoting mechanisms on $v expansion side: one protects
 * $v from brace expansion, and other additionally protects "$v" against globbing.
 * We have only second one.
 */

#if ENABLE_HUSH_BRACE_EXPANSION
# define MAYBE_BRACES "{}"
#else
# define MAYBE_BRACES ""
#endif

/* My analysis of quoting semantics tells me that state information
 * is associated with a destination, not a source.
 */
static void o_addqchr(o_string *o, int ch)
{
	int sz = 1;
	/* '-' is included because of this case:
	 * >filename0 >filename1 >filename9; v='-'; echo filename[0"$v"9]
	 */
	char *found = strchr("*?[-\\" MAYBE_BRACES, ch);
	if (found)
		sz++;
	o_grow_by(o, sz);
	if (found) {
		o->data[o->length] = '\\';
		o->length++;
	}
	o->data[o->length] = ch;
	o->length++;
	o->data[o->length] = '\0';
}

static void o_addQchr(o_string *o, int ch)
{
	int sz = 1;
	if ((o->o_expflags & EXP_FLAG_ESC_GLOB_CHARS)
	 && strchr("*?[-\\" MAYBE_BRACES, ch)
	) {
		sz++;
		o->data[o->length] = '\\';
		o->length++;
	}
	o_grow_by(o, sz);
	o->data[o->length] = ch;
	o->length++;
	o->data[o->length] = '\0';
}

static void o_addqblock(o_string *o, const char *str, int len)
{
	while (len) {
		char ch;
		int sz;
		int ordinary_cnt = strcspn(str, "*?[-\\" MAYBE_BRACES);
		if (ordinary_cnt > len) /* paranoia */
			ordinary_cnt = len;
		o_addblock(o, str, ordinary_cnt);
		if (ordinary_cnt == len)
			return; /* NUL is already added by o_addblock */
		str += ordinary_cnt;
		len -= ordinary_cnt + 1; /* we are processing + 1 char below */

		ch = *str++;
		sz = 1;
		if (ch) { /* it is necessarily one of "*?[-\\" MAYBE_BRACES */
			sz++;
			o->data[o->length] = '\\';
			o->length++;
		}
		o_grow_by(o, sz);
		o->data[o->length] = ch;
		o->length++;
	}
	o->data[o->length] = '\0';
}

static void o_addQblock(o_string *o, const char *str, int len)
{
	if (!(o->o_expflags & EXP_FLAG_ESC_GLOB_CHARS)) {
		o_addblock(o, str, len);
		return;
	}
	o_addqblock(o, str, len);
}

static void o_addQstr(o_string *o, const char *str)
{
	o_addQblock(o, str, strlen(str));
}

/* A special kind of o_string for $VAR and `cmd` expansion.
 * It contains char* list[] at the beginning, which is grown in 16 element
 * increments. Actual string data starts at the next multiple of 16 * (char*).
 * list[i] contains an INDEX (int!) into this string data.
 * It means that if list[] needs to grow, data needs to be moved higher up
 * but list[i]'s need not be modified.
 * NB: remembering how many list[i]'s you have there is crucial.
 * o_finalize_list() operation post-processes this structure - calculates
 * and stores actual char* ptrs in list[]. Oh, it NULL terminates it as well.
 */
#if DEBUG_EXPAND || DEBUG_GLOB
static void debug_print_list(const char *prefix, o_string *o, int n)
{
	char **list = (char**)o->data;
	int string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);
	int i = 0;

	indent();
	fdprintf(2, "%s: list:%p n:%d string_start:%d length:%d maxlen:%d glob:%d quoted:%d escape:%d\n",
			prefix, list, n, string_start, o->length, o->maxlen,
			!!(o->o_expflags & EXP_FLAG_GLOB),
			o->has_quoted_part,
			!!(o->o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
	while (i < n) {
		indent();
		fdprintf(2, " list[%d]=%d '%s' %p\n", i, (int)(uintptr_t)list[i],
				o->data + (int)(uintptr_t)list[i] + string_start,
				o->data + (int)(uintptr_t)list[i] + string_start);
		i++;
	}
	if (n) {
		const char *p = o->data + (int)(uintptr_t)list[n - 1] + string_start;
		indent();
		fdprintf(2, " total_sz:%ld\n", (long)((p + strlen(p) + 1) - o->data));
	}
}
#else
# define debug_print_list(prefix, o, n) ((void)0)
#endif

/* n = o_save_ptr_helper(str, n) "starts new string" by storing an index value
 * in list[n] so that it points past last stored byte so far.
 * It returns n+1. */
static int o_save_ptr_helper(o_string *o, int n)
{
	char **list = (char**)o->data;
	int string_start;
	int string_len;

	if (!o->has_empty_slot) {
		string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);
		string_len = o->length - string_start;
		if (!(n & 0xf)) { /* 0, 0x10, 0x20...? */
			debug_printf_list("list[%d]=%d string_start=%d (growing)\n", n, string_len, string_start);
			/* list[n] points to string_start, make space for 16 more pointers */
			o->maxlen += 0x10 * sizeof(list[0]);
			o->data = xrealloc(o->data, o->maxlen + 1);
			list = (char**)o->data;
			memmove(list + n + 0x10, list + n, string_len);
			/*
			 * expand_on_ifs() has a "previous argv[] ends in IFS?"
			 * check. (grep for -prev-ifs-check-).
			 * Ensure that argv[-1][last] is not garbage
			 * but zero bytes, to save index check there.
			 */
			list[n + 0x10 - 1] = 0;
			o->length += 0x10 * sizeof(list[0]);
		} else {
			debug_printf_list("list[%d]=%d string_start=%d\n",
					n, string_len, string_start);
		}
	} else {
		/* We have empty slot at list[n], reuse without growth */
		string_start = ((n+1 + 0xf) & ~0xf) * sizeof(list[0]); /* NB: n+1! */
		string_len = o->length - string_start;
		debug_printf_list("list[%d]=%d string_start=%d (empty slot)\n",
				n, string_len, string_start);
		o->has_empty_slot = 0;
	}
	o->has_quoted_part = 0;
	list[n] = (char*)(uintptr_t)string_len;
	return n + 1;
}

/* "What was our last o_save_ptr'ed position (byte offset relative o->data)?" */
static int o_get_last_ptr(o_string *o, int n)
{
	char **list = (char**)o->data;
	int string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);

	return ((int)(uintptr_t)list[n-1]) + string_start;
}

/*
 * Globbing routines.
 *
 * Most words in commands need to be globbed, even ones which are
 * (single or double) quoted. This stems from the possiblity of
 * constructs like "abc"* and 'abc'* - these should be globbed.
 * Having a different code path for fully-quoted strings ("abc",
 * 'abc') would only help performance-wise, but we still need
 * code for partially-quoted strings.
 *
 * Unfortunately, if we want to match bash and ash behavior in all cases,
 * the logic can't be "shell-syntax argument is first transformed
 * to a string, then globbed, and if globbing does not match anything,
 * it is used verbatim". Here are two examples where it fails:
 *
 * 	echo 'b\*'?
 *
 * The globbing can't be avoided (because of '?' at the end).
 * The glob pattern is: b\\\*? - IOW, both \ and * are literals
 * and are glob-escaped. If this does not match, bash/ash print b\*?
 * - IOW: they "unbackslash" the glob pattern.
 * Now, look at this:
 *
 * 	v='\\\*'; echo b$v?
 *
 * The glob pattern is the same here: b\\\*? - the unquoted $v expansion
 * should be used as glob pattern with no changes. However, if glob
 * does not match, bash/ash print b\\\*? - NOT THE SAME as first example!
 *
 * ash implements this by having an encoded representation of the word
 * to glob, which IS NOT THE SAME as the glob pattern - it has more data.
 * Glob pattern is derived from it. If glob fails, the decision what result
 * should be is made using that encoded representation. Not glob pattern.
 */

#if ENABLE_HUSH_BRACE_EXPANSION
/* There in a GNU extension, GLOB_BRACE, but it is not usable:
 * first, it processes even {a} (no commas), second,
 * I didn't manage to make it return strings when they don't match
 * existing files. Need to re-implement it.
 */

/* Helper */
static int glob_needed(const char *s)
{
	while (*s) {
		if (*s == '\\') {
			if (!s[1])
				return 0;
			s += 2;
			continue;
		}
		if (*s == '*' || *s == '[' || *s == '?' || *s == '{')
			return 1;
		s++;
	}
	return 0;
}
/* Return pointer to next closing brace or to comma */
static const char *next_brace_sub(const char *cp)
{
	unsigned depth = 0;
	cp++;
	while (*cp != '\0') {
		if (*cp == '\\') {
			if (*++cp == '\0')
				break;
			cp++;
			continue;
		}
		if ((*cp == '}' && depth-- == 0) || (*cp == ',' && depth == 0))
			break;
		if (*cp++ == '{')
			depth++;
	}

	return *cp != '\0' ? cp : NULL;
}
/* Recursive brace globber. Note: may garble pattern[]. */
static int glob_brace(char *pattern, o_string *o, int n)
{
	char *new_pattern_buf;
	const char *begin;
	const char *next;
	const char *rest;
	const char *p;
	size_t rest_len;

	debug_printf_glob("glob_brace('%s')\n", pattern);

	begin = pattern;
	while (1) {
		if (*begin == '\0')
			goto simple_glob;
		if (*begin == '{') {
			/* Find the first sub-pattern and at the same time
			 * find the rest after the closing brace */
			next = next_brace_sub(begin);
			if (next == NULL) {
				/* An illegal expression */
				goto simple_glob;
			}
			if (*next == '}') {
				/* "{abc}" with no commas - illegal
				 * brace expr, disregard and skip it */
				begin = next + 1;
				continue;
			}
			break;
		}
		if (*begin == '\\' && begin[1] != '\0')
			begin++;
		begin++;
	}
	debug_printf_glob("begin:%s\n", begin);
	debug_printf_glob("next:%s\n", next);

	/* Now find the end of the whole brace expression */
	rest = next;
	while (*rest != '}') {
		rest = next_brace_sub(rest);
		if (rest == NULL) {
			/* An illegal expression */
			goto simple_glob;
		}
		debug_printf_glob("rest:%s\n", rest);
	}
	rest_len = strlen(++rest) + 1;

	/* We are sure the brace expression is well-formed */

	/* Allocate working buffer large enough for our work */
	new_pattern_buf = xmalloc(strlen(pattern));

	/* We have a brace expression.  BEGIN points to the opening {,
	 * NEXT points past the terminator of the first element, and REST
	 * points past the final }.  We will accumulate result names from
	 * recursive runs for each brace alternative in the buffer using
	 * GLOB_APPEND.  */

	p = begin + 1;
	while (1) {
		/* Construct the new glob expression */
		memcpy(
			mempcpy(
				mempcpy(new_pattern_buf,
					/* We know the prefix for all sub-patterns */
					pattern, begin - pattern),
				p, next - p),
			rest, rest_len);

		/* Note: glob_brace() may garble new_pattern_buf[].
		 * That's why we re-copy prefix every time (1st memcpy above).
		 */
		n = glob_brace(new_pattern_buf, o, n);
		if (*next == '}') {
			/* We saw the last entry */
			break;
		}
		p = next + 1;
		next = next_brace_sub(next);
	}
	free(new_pattern_buf);
	return n;

 simple_glob:
	{
		int gr;
		glob_t globdata;

		memset(&globdata, 0, sizeof(globdata));
		gr = glob(pattern, 0, NULL, &globdata);
		debug_printf_glob("glob('%s'):%d\n", pattern, gr);
		if (gr != 0) {
			if (gr == GLOB_NOMATCH) {
				globfree(&globdata);
				/* NB: garbles parameter */
				unbackslash(pattern);
				o_addstr_with_NUL(o, pattern);
				debug_printf_glob("glob pattern '%s' is literal\n", pattern);
				return o_save_ptr_helper(o, n);
			}