editors/sed.c

/* vi: set sw=4 ts=4: */
/*
 * sed.c - very minimalist version of sed
 *
 * Copyright (C) 1999,2000,2001 by Lineo, inc. and Mark Whitley
 * Copyright (C) 1999,2000,2001 by Mark Whitley <markw@codepoet.org>
 * Copyright (C) 2002  Matt Kraai
 * Copyright (C) 2003 by Glenn McGrath <bug1@iinet.net.au>
 * Copyright (C) 2003,2004 by Rob Landley <rob@landley.net>
 *
 * MAINTAINER: Rob Landley <rob@landley.net>
 *
 * Licensed under GPL version 2, see file LICENSE in this tarball for details.
 */

/* Code overview.

  Files are laid out to avoid unnecessary function declarations.  So for
  example, every function add_cmd calls occurs before add_cmd in this file.

  add_cmd() is called on each line of sed command text (from a file or from
  the command line).  It calls get_address() and parse_cmd_args().  The
  resulting sed_cmd_t structures are appended to a linked list
  (bbg.sed_cmd_head/bbg.sed_cmd_tail).

  add_input_file() adds a FILE * to the list of input files.  We need to
  know all input sources ahead of time to find the last line for the $ match.

  process_files() does actual sedding, reading data lines from each input FILE *
  (which could be stdin) and applying the sed command list (sed_cmd_head) to
  each of the resulting lines.

  sed_main() is where external code calls into this, with a command line.
*/


/*
	Supported features and commands in this version of sed:

	 - comments ('#')
	 - address matching: num|/matchstr/[,num|/matchstr/|$]command
	 - commands: (p)rint, (d)elete, (s)ubstitue (with g & I flags)
	 - edit commands: (a)ppend, (i)nsert, (c)hange
	 - file commands: (r)ead
	 - backreferences in substitution expressions (\0, \1, \2...\9)
	 - grouped commands: {cmd1;cmd2}
	 - transliteration (y/source-chars/dest-chars/)
	 - pattern space hold space storing / swapping (g, h, x)
	 - labels / branching (: label, b, t, T)

	 (Note: Specifying an address (range) to match is *optional*; commands
	 default to the whole pattern space if no specific address match was
	 requested.)

	Todo:
	 - Create a wrapper around regex to make libc's regex conform with sed

	Reference http://www.opengroup.org/onlinepubs/007904975/utilities/sed.html
*/

#include "busybox.h"
#include "xregex.h"

/* Each sed command turns into one of these structures. */
typedef struct sed_cmd_s {
	/* Ordered by alignment requirements: currently 36 bytes on x86 */

	/* address storage */
	regex_t *beg_match;     /* sed -e '/match/cmd' */
	regex_t *end_match;     /* sed -e '/match/,/end_match/cmd' */
	regex_t *sub_match;     /* For 's/sub_match/string/' */
	int beg_line;           /* 'sed 1p'   0 == apply commands to all lines */
	int end_line;           /* 'sed 1,3p' 0 == one line only. -1 = last line ($) */

	FILE *sw_file;          /* File (sw) command writes to, -1 for none. */
	char *string;           /* Data string for (saicytb) commands. */

	unsigned short which_match;     /* (s) Which match to replace (0 for all) */

	/* Bitfields (gcc won't group them if we don't) */
	unsigned int invert:1;          /* the '!' after the address */
	unsigned int in_match:1;        /* Next line also included in match? */
	unsigned int sub_p:1;           /* (s) print option */

	char sw_last_char;                  /* Last line written by (sw) had no '\n' */

	/* GENERAL FIELDS */
	char cmd;               /* The command char: abcdDgGhHilnNpPqrstwxy:={} */
	struct sed_cmd_s *next; /* Next command (linked list, NULL terminated) */
} sed_cmd_t;

static const char *const semicolon_whitespace = "; \n\r\t\v";

struct sed_globals {
	/* options */
	int be_quiet, regex_type;
	FILE *nonstdout;
	char *outname, *hold_space;

	/* List of input files */
	int input_file_count, current_input_file;
	FILE **input_file_list;

	regmatch_t regmatch[10];
	regex_t *previous_regex_ptr;

	/* linked list of sed commands */
	sed_cmd_t sed_cmd_head, *sed_cmd_tail;

	/* Linked list of append lines */
	llist_t *append_head;

	char *add_cmd_line;

	struct pipeline {
		char *buf;	/* Space to hold string */
		int idx;	/* Space used */
		int len;	/* Space allocated */
	} pipeline;
} bbg;


#if ENABLE_FEATURE_CLEAN_UP
static void sed_free_and_close_stuff(void)
{
	sed_cmd_t *sed_cmd = bbg.sed_cmd_head.next;

	llist_free(bbg.append_head, free);

	while (sed_cmd) {
		sed_cmd_t *sed_cmd_next = sed_cmd->next;

		if (sed_cmd->sw_file)
			xprint_and_close_file(sed_cmd->sw_file);

		if (sed_cmd->beg_match) {
			regfree(sed_cmd->beg_match);
			free(sed_cmd->beg_match);
		}
		if (sed_cmd->end_match) {
			regfree(sed_cmd->end_match);
			free(sed_cmd->end_match);
		}
		if (sed_cmd->sub_match) {
			regfree(sed_cmd->sub_match);
			free(sed_cmd->sub_match);
		}
		free(sed_cmd->string);
		free(sed_cmd);
		sed_cmd = sed_cmd_next;
	}

	if (bbg.hold_space) free(bbg.hold_space);

	while (bbg.current_input_file < bbg.input_file_count)
		fclose(bbg.input_file_list[bbg.current_input_file++]);
}
#else
void sed_free_and_close_stuff(void);
#endif

/* If something bad happens during -i operation, delete temp file */

static void cleanup_outname(void)
{
	if (bbg.outname) unlink(bbg.outname);
}

/* strdup, replacing "\n" with '\n', and "\delimiter" with 'delimiter' */

static void parse_escapes(char *dest, char *string, int len, char from, char to)
{
	int i = 0;

	while (i < len) {
		if (string[i] == '\\') {
			if (!to || string[i+1] == from) {
				*dest++ = to ? to : string[i+1];
				i += 2;
				continue;
			}
			*dest++ = string[i++];
		}
		*dest++ = string[i++];
	}
	*dest = 0;
}

static char *copy_parsing_escapes(char *string, int len)
{
	char *dest = xmalloc(len + 1);

	parse_escapes(dest, string, len, 'n', '\n');
	return dest;
}


/*
 * index_of_next_unescaped_regexp_delim - walks left to right through a string
 * beginning at a specified index and returns the index of the next regular
 * expression delimiter (typically a forward * slash ('/')) not preceded by
 * a backslash ('\').  A negative delimiter disables square bracket checking.
 */
static int index_of_next_unescaped_regexp_delim(int delimiter, char *str)
{
	int bracket = -1;
	int escaped = 0;
	int idx = 0;
	char ch;

	if (delimiter < 0) {
		bracket--;
		delimiter = -delimiter;
	}

	for (; (ch = str[idx]); idx++) {
		if (bracket >= 0) {
			if (ch == ']' && !(bracket == idx - 1 || (bracket == idx - 2
					&& str[idx - 1] == '^')))
				bracket = -1;
		} else if (escaped)
			escaped = 0;
		else if (ch == '\\')
			escaped = 1;
		else if (bracket == -1 && ch == '[')
			bracket = idx;
		else if (ch == delimiter)
			return idx;
	}

	/* if we make it to here, we've hit the end of the string */
	bb_error_msg_and_die("unmatched '%c'", delimiter);
}

/*
 *  Returns the index of the third delimiter
 */
static int parse_regex_delim(char *cmdstr, char **match, char **replace)
{
	char *cmdstr_ptr = cmdstr;
	char delimiter;
	int idx = 0;

	/* verify that the 's' or 'y' is followed by something.  That something
	 * (typically a 'slash') is now our regexp delimiter... */
	if (*cmdstr == '\0')
		bb_error_msg_and_die("bad format in substitution expression");
	delimiter = *cmdstr_ptr++;

	/* save the match string */
	idx = index_of_next_unescaped_regexp_delim(delimiter, cmdstr_ptr);
	*match = copy_parsing_escapes(cmdstr_ptr, idx);

	/* save the replacement string */
	cmdstr_ptr += idx + 1;
	idx = index_of_next_unescaped_regexp_delim(-delimiter, cmdstr_ptr);
	*replace = copy_parsing_escapes(cmdstr_ptr, idx);

	return ((cmdstr_ptr - cmdstr) + idx);
}

/*
 * returns the index in the string just past where the address ends.
 */
static int get_address(char *my_str, int *linenum, regex_t ** regex)
{
	char *pos = my_str;

	if (isdigit(*my_str)) {
		*linenum = strtol(my_str, &pos, 10);
		/* endstr shouldnt ever equal NULL */
	} else if (*my_str == '$') {
		*linenum = -1;
		pos++;
	} else if (*my_str == '/' || *my_str == '\\') {
		int next;
		char delimiter;
		char *temp;

		delimiter = '/';
		if (*my_str == '\\') delimiter = *++pos;
		next = index_of_next_unescaped_regexp_delim(delimiter, ++pos);
		temp = copy_parsing_escapes(pos, next);
		*regex = xmalloc(sizeof(regex_t));
		xregcomp(*regex, temp, bbg.regex_type|REG_NEWLINE);
		free(temp);
		/* Move position to next character after last delimiter */
		pos += (next+1);
	}
	return pos - my_str;
}

/* Grab a filename.  Whitespace at start is skipped, then goes to EOL. */
static int parse_file_cmd(sed_cmd_t *sed_cmd, char *filecmdstr, char **retval)
{
	int start = 0, idx, hack = 0;

	/* Skip whitespace, then grab filename to end of line */
	while (isspace(filecmdstr[start])) start++;
	idx = start;
	while (filecmdstr[idx] && filecmdstr[idx] != '\n') idx++;

	/* If lines glued together, put backslash back. */
	if (filecmdstr[idx] == '\n') hack = 1;
	if (idx == start)
		bb_error_msg_and_die("empty filename");
	*retval = xstrndup(filecmdstr+start, idx-start+hack+1);
	if (hack) (*retval)[idx] = '\\';

	return idx;
}

static int parse_subst_cmd(sed_cmd_t *sed_cmd, char *substr)
{
	int cflags = bbg.regex_type;
	char *match;
	int idx = 0;

	/*
	 * A substitution command should look something like this:
	 *    s/match/replace/ #gIpw
	 *    ||     |        |||
	 *    mandatory       optional
	 */
	idx = parse_regex_delim(substr, &match, &sed_cmd->string);

	/* determine the number of back references in the match string */
	/* Note: we compute this here rather than in the do_subst_command()
	 * function to save processor time, at the expense of a little more memory
	 * (4 bits) per sed_cmd */

	/* process the flags */

	sed_cmd->which_match = 1;
	while (substr[++idx]) {
		/* Parse match number */
		if (isdigit(substr[idx])) {
			if (match[0] != '^') {
				/* Match 0 treated as all, multiple matches we take the last one. */
				char *pos = substr + idx;
				/* FIXME: error check? */
				sed_cmd->which_match = (unsigned short)strtol(substr+idx, &pos, 10);
				idx = pos - substr;
			}
			continue;
		}
		/* Skip spaces */
		if (isspace(substr[idx])) continue;

		switch (substr[idx]) {
		/* Replace all occurrences */
		case 'g':
			if (match[0] != '^') sed_cmd->which_match = 0;
			break;
		/* Print pattern space */
		case 'p':
			sed_cmd->sub_p = 1;
			break;
		/* Write to file */
		case 'w':
		{
			char *temp;
			idx += parse_file_cmd(sed_cmd, substr+idx, &temp);

			break;
		}
		/* Ignore case (gnu exension) */
		case 'I':
			cflags |= REG_ICASE;
			break;
		/* Comment */
		case '#':
			while (substr[++idx]) /*skip all*/;
			/* Fall through */
		/* End of command */
		case ';':
		case '}':
			goto out;
		default:
			bb_error_msg_and_die("bad option in substitution expression");
		}
	}
out:
	/* compile the match string into a regex */
	if (*match != '\0') {
		/* If match is empty, we use last regex used at runtime */
		sed_cmd->sub_match = xmalloc(sizeof(regex_t));
		xregcomp(sed_cmd->sub_match, match, cflags);
	}
	free(match);

	return idx;
}

/*
 *  Process the commands arguments
 */
static char *parse_cmd_args(sed_cmd_t *sed_cmd, char *cmdstr)
{
	/* handle (s)ubstitution command */
	if (sed_cmd->cmd == 's')
		cmdstr += parse_subst_cmd(sed_cmd, cmdstr);
	/* handle edit cmds: (a)ppend, (i)nsert, and (c)hange */
	else if (strchr("aic", sed_cmd->cmd)) {
		if ((sed_cmd->end_line || sed_cmd->end_match) && sed_cmd->cmd != 'c')
			bb_error_msg_and_die
				("only a beginning address can be specified for edit commands");
		for (;;) {
			if (*cmdstr == '\n' || *cmdstr == '\\') {
				cmdstr++;
				break;
			} else if (isspace(*cmdstr))
				cmdstr++;
			else
				break;
		}
		sed_cmd->string = xstrdup(cmdstr);
		parse_escapes(sed_cmd->string, sed_cmd->string, strlen(cmdstr), 0, 0);
		cmdstr += strlen(cmdstr);
	/* handle file cmds: (r)ead */
	} else if (strchr("rw", sed_cmd->cmd)) {
		if (sed_cmd->end_line || sed_cmd->end_match)
			bb_error_msg_and_die("command only uses one address");
		cmdstr += parse_file_cmd(sed_cmd, cmdstr, &sed_cmd->string);
		if (sed_cmd->cmd == 'w') {
			sed_cmd->sw_file = xfopen(sed_cmd->string, "w");
			sed_cmd->sw_last_char = '\n';
		}
	/* handle branch commands */
	} else if (strchr(":btT", sed_cmd->cmd)) {
		int length;

		cmdstr = skip_whitespace(cmdstr);
		length = strcspn(cmdstr, semicolon_whitespace);
		if (length) {
			sed_cmd->string = xstrndup(cmdstr, length);
			cmdstr += length;
		}
	}
	/* translation command */
	else if (sed_cmd->cmd == 'y') {
		char *match, *replace;
		int i = cmdstr[0];

		cmdstr += parse_regex_delim(cmdstr, &match, &replace)+1;
		/* \n already parsed, but \delimiter needs unescaping. */
		parse_escapes(match, match, strlen(match), i, i);
		parse_escapes(replace, replace, strlen(replace), i, i);

		sed_cmd->string = xzalloc((strlen(match) + 1) * 2);
		for (i = 0; match[i] && replace[i]; i++) {
			sed_cmd->string[i*2] = match[i];
			sed_cmd->string[i*2+1] = replace[i];
		}
		free(match);
		free(replace);
	}
	/* if it wasnt a single-letter command that takes no arguments
	 * then it must be an invalid command.
	 */
	else if (strchr("dDgGhHlnNpPqx={}", sed_cmd->cmd) == 0) {
		bb_error_msg_and_die("unsupported command %c", sed_cmd->cmd);
	}

	/* give back whatever's left over */
	return cmdstr;
}


/* Parse address+command sets, skipping comment lines. */

static void add_cmd(char *cmdstr)
{
	sed_cmd_t *sed_cmd;
	int temp;

	/* Append this line to any unfinished line from last time. */
	if (bbg.add_cmd_line) {
		cmdstr = xasprintf("%s\n%s", bbg.add_cmd_line, cmdstr);
		free(bbg.add_cmd_line);
		bbg.add_cmd_line = cmdstr;
	}

	/* If this line ends with backslash, request next line. */
	temp = strlen(cmdstr);
	if (temp && cmdstr[temp-1] == '\\') {
		if (!bbg.add_cmd_line)
			bbg.add_cmd_line = xstrdup(cmdstr);
		bbg.add_cmd_line[temp-1] = 0;
		return;
	}

	/* Loop parsing all commands in this line. */
	while (*cmdstr) {
		/* Skip leading whitespace and semicolons */
		cmdstr += strspn(cmdstr, semicolon_whitespace);

		/* If no more commands, exit. */
		if (!*cmdstr) break;

		/* if this is a comment, jump past it and keep going */
		if (*cmdstr == '#') {
			/* "#n" is the same as using -n on the command line */
			if (cmdstr[1] == 'n')
				bbg.be_quiet++;
			cmdstr = strpbrk(cmdstr, "\n\r");
			if (!cmdstr) break;
			continue;
		}

		/* parse the command
		 * format is: [addr][,addr][!]cmd
		 *            |----||-----||-|
		 *            part1 part2  part3
		 */

		sed_cmd = xzalloc(sizeof(sed_cmd_t));

		/* first part (if present) is an address: either a '$', a number or a /regex/ */
		cmdstr += get_address(cmdstr, &sed_cmd->beg_line, &sed_cmd->beg_match);

		/* second part (if present) will begin with a comma */
		if (*cmdstr == ',') {
			int idx;

			cmdstr++;
			idx = get_address(cmdstr, &sed_cmd->end_line, &sed_cmd->end_match);
			if (!idx)
				bb_error_msg_and_die("no address after comma");
			cmdstr += idx;
		}

		/* skip whitespace before the command */
		cmdstr = skip_whitespace(cmdstr);

		/* Check for inversion flag */
		if (*cmdstr == '!') {
			sed_cmd->invert = 1;
			cmdstr++;

			/* skip whitespace before the command */
			cmdstr = skip_whitespace(cmdstr);
		}

		/* last part (mandatory) will be a command */
		if (!*cmdstr)
			bb_error_msg_and_die("missing command");
		sed_cmd->cmd = *(cmdstr++);
		cmdstr = parse_cmd_args(sed_cmd, cmdstr);

		/* Add the command to the command array */
		bbg.sed_cmd_tail->next = sed_cmd;
		bbg.sed_cmd_tail = bbg.sed_cmd_tail->next;
	}

	/* If we glued multiple lines together, free the memory. */
	free(bbg.add_cmd_line);
	bbg.add_cmd_line = NULL;
}

/* Append to a string, reallocating memory as necessary. */

#define PIPE_GROW 64

static void pipe_putc(char c)
{
	if (bbg.pipeline.idx == bbg.pipeline.len) {
		bbg.pipeline.buf = xrealloc(bbg.pipeline.buf,
				bbg.pipeline.len + PIPE_GROW);
		bbg.pipeline.len += PIPE_GROW;
	}
	bbg.pipeline.buf[bbg.pipeline.idx++] = c;
}

static void do_subst_w_backrefs(char *line, char *replace)
{
	int i,j;

	/* go through the replacement string */
	for (i = 0; replace[i]; i++) {
		/* if we find a backreference (\1, \2, etc.) print the backref'ed * text */
		if (replace[i] == '\\') {
			unsigned backref = replace[++i] - '0';
			if (backref <= 9) {
				/* print out the text held in bbg.regmatch[backref] */
				if (bbg.regmatch[backref].rm_so != -1) {
					j = bbg.regmatch[backref].rm_so;
					while (j < bbg.regmatch[backref].rm_eo)
						pipe_putc(line[j++]);
				}
				continue;
			}
			/* I _think_ it is impossible to get '\' to be
			 * the last char in replace string. Thus we dont check
			 * for replace[i] == NUL. (counterexample anyone?) */
			/* if we find a backslash escaped character, print the character */
			pipe_putc(replace[i]);
			continue;
		}
		/* if we find an unescaped '&' print out the whole matched text. */
		if (replace[i] == '&') {
			j = bbg.regmatch[0].rm_so;
			while (j < bbg.regmatch[0].rm_eo)
				pipe_putc(line[j++]);
			continue;
		}
		/* Otherwise just output the character. */
		pipe_putc(replace[i]);
	}
}

static int do_subst_command(sed_cmd_t *sed_cmd, char **line)
{
	char *oldline = *line;
	int altered = 0;
	int match_count = 0;
	regex_t *current_regex;

	/* Handle empty regex. */
	if (sed_cmd->sub_match == NULL) {
		current_regex = bbg.previous_regex_ptr;
		if (!current_regex)
			bb_error_msg_and_die("no previous regexp");
	} else
		bbg.previous_regex_ptr = current_regex = sed_cmd->sub_match;

	/* Find the first match */
	if (REG_NOMATCH == regexec(current_regex, oldline, 10, bbg.regmatch, 0))
		return 0;

	/* Initialize temporary output buffer. */
	bbg.pipeline.buf = xmalloc(PIPE_GROW);
	bbg.pipeline.len = PIPE_GROW;
	bbg.pipeline.idx = 0;

	/* Now loop through, substituting for matches */
	do {
		int i;

		/* Work around bug in glibc regexec, demonstrated by:
		   echo " a.b" | busybox sed 's [^ .]* x g'
		   The match_count check is so not to break
		   echo "hi" | busybox sed 's/^/!/g' */
		if (!bbg.regmatch[0].rm_so && !bbg.regmatch[0].rm_eo && match_count) {
			pipe_putc(*oldline++);
			continue;
		}

		match_count++;

		/* If we aren't interested in this match, output old line to
		   end of match and continue */
		if (sed_cmd->which_match && sed_cmd->which_match != match_count) {
			for (i = 0; i < bbg.regmatch[0].rm_eo; i++)
				pipe_putc(*oldline++);
			continue;
		}

		/* print everything before the match */
		for (i = 0; i < bbg.regmatch[0].rm_so; i++)
			pipe_putc(oldline[i]);

		/* then print the substitution string */
		do_subst_w_backrefs(oldline, sed_cmd->string);

		/* advance past the match */
		oldline += bbg.regmatch[0].rm_eo;
		/* flag that something has changed */
		altered++;

		/* if we're not doing this globally, get out now */
		if (sed_cmd->which_match) break;
	} while (*oldline && (regexec(current_regex, oldline, 10, bbg.regmatch, 0) != REG_NOMATCH));

	/* Copy rest of string into output pipeline */

	while (*oldline)
		pipe_putc(*oldline++);
	pipe_putc(0);

	free(*line);
	*line = bbg.pipeline.buf;
	return altered;
}

/* Set command pointer to point to this label.  (Does not handle null label.) */
static sed_cmd_t *branch_to(char *label)
{
	sed_cmd_t *sed_cmd;

	for (sed_cmd = bbg.sed_cmd_head.next; sed_cmd; sed_cmd = sed_cmd->next) {
		if (sed_cmd->cmd == ':' && sed_cmd->string && !strcmp(sed_cmd->string, label)) {
			return sed_cmd;
		}
	}
	bb_error_msg_and_die("can't find label for jump to '%s'", label);
}

static void append(char *s)
{
	llist_add_to_end(&bbg.append_head, xstrdup(s));
}

static void flush_append(void)
{
	char *data;

	/* Output appended lines. */
	while ((data = (char *)llist_pop(&bbg.append_head))) {
		fprintf(bbg.nonstdout, "%s\n", data);
		free(data);
	}
}

static void add_input_file(FILE *file)
{
	bbg.input_file_list = xrealloc(bbg.input_file_list,
			(bbg.input_file_count + 1) * sizeof(FILE *));
	bbg.input_file_list[bbg.input_file_count++] = file;
}

/* Get next line of input from bbg.input_file_list, flushing append buffer and
 * noting if we ran out of files without a newline on the last line we read.
 */
enum {
	NO_EOL_CHAR = 1,
};
static char *get_next_line(char *gets_char)
{
	char *temp = NULL;
	int len;
	char gc;

	flush_append();

	/* will be returned if last line in the file
	 * doesn't end with either '\n' or '\0' */
	gc = NO_EOL_CHAR;
	while (bbg.current_input_file < bbg.input_file_count) {
		/* Read line up to a newline or NUL byte, inclusive,
		 * return malloc'ed char[]. length of the chunk read
		 * is stored in len. NULL if EOF/error */
		temp = bb_get_chunk_from_file(
			bbg.input_file_list[bbg.current_input_file], &len);
		if (temp) {
			/* len > 0 here, it's ok to do temp[len-1] */
			char c = temp[len-1];
			if (c == '\n' || c == '\0') {
				temp[len-1] = '\0';
				gc = c;
			}
			/* else we put NO_EOL_CHAR into *gets_char */
			break;

		/* NB: I had the idea of peeking next file(s) and returning
		 * NO_EOL_CHAR only if it is the *last* non-empty
		 * input file. But there is a case where this won't work:
		 * file1: "a woo\nb woo"
		 * file2: "c no\nd no"
		 * sed -ne 's/woo/bang/p' input1 input2 => "a bang\nb bang"
		 * (note: *no* newline after "b bang"!) */
		}
		/* Close this file and advance to next one */
		fclose(bbg.input_file_list[bbg.current_input_file++]);
	}
	*gets_char = gc;
	return temp;
}

/* Output line of text. */
/* Note:
 * The tricks with NO_EOL_CHAR and last_puts_char are there to emulate gnu sed.
 * Without them, we had this:
 * echo -n thingy >z1
 * echo -n again >z2
 * >znull
 * sed "s/i/z/" z1 z2 znull | hexdump -vC
 * output:
 * gnu sed 4.1.5:
 * 00000000  74 68 7a 6e 67 79 0a 61  67 61 7a 6e              |thzngy.agazn|
 * bbox:
 * 00000000  74 68 7a 6e 67 79 61 67  61 7a 6e                 |thzngyagazn|
 */
static void puts_maybe_newline(char *s, FILE *file, char *last_puts_char, char last_gets_char)
{
	char lpc = *last_puts_char;

	/* Is this a first line from new file
	 * and old file didn't end with '\n' or '\0'? */
	if (lpc != '\n' && lpc != '\0') {
		fputc('\n', file);
		lpc = '\n';
	}
	fputs(s, file);
	/* 'x' - just something which is not '\n', '\0' or NO_EOL_CHAR */
	if (s[0])
		lpc = 'x';
	if (last_gets_char != NO_EOL_CHAR) { /* had trailing '\n' or '\0'? */
		fputc(last_gets_char, file);
		lpc = last_gets_char;
	}
	if (ferror(file)) {
		xfunc_error_retval = 4;  /* It's what gnu sed exits with... */
		bb_error_msg_and_die(bb_msg_write_error);
	}
	*last_puts_char = lpc;
}

#define sed_puts(s, n) (puts_maybe_newline(s, bbg.nonstdout, &last_puts_char, n))

/* Process all the lines in all the files */

static void process_files(void)
{
	char *pattern_space, *next_line;
	int linenum = 0;
	char last_puts_char = '\n';
	char last_gets_char, next_gets_char;
	sed_cmd_t *sed_cmd;
	int substituted;

	/* Prime the pump */
	next_line = get_next_line(&next_gets_char);

	/* go through every line in each file */
again:
	substituted = 0;

	/* Advance to next line.  Stop if out of lines. */
	pattern_space = next_line;
	if (!pattern_space) return;
	last_gets_char = next_gets_char;

	/* Read one line in advance so we can act on the last line,
	 * the '$' address */
	next_line = get_next_line(&next_gets_char);
	linenum++;
restart:
	/* for every line, go through all the commands */
	for (sed_cmd = bbg.sed_cmd_head.next; sed_cmd; sed_cmd = sed_cmd->next) {
		int old_matched, matched;

		old_matched = sed_cmd->in_match;

		/* Determine if this command matches this line: */

		/* Are we continuing a previous multi-line match? */
		sed_cmd->in_match = sed_cmd->in_match
			/* Or is no range necessary? */
			|| (!sed_cmd->beg_line && !sed_cmd->end_line
				&& !sed_cmd->beg_match && !sed_cmd->end_match)
			/* Or did we match the start of a numerical range? */
			|| (sed_cmd->beg_line > 0 && (sed_cmd->beg_line == linenum))
			/* Or does this line match our begin address regex? */
			|| (sed_cmd->beg_match &&
			    !regexec(sed_cmd->beg_match, pattern_space, 0, NULL, 0))
			/* Or did we match last line of input? */
			|| (sed_cmd->beg_line == -1 && next_line == NULL);

		/* Snapshot the value */

		matched = sed_cmd->in_match;

		/* Is this line the end of the current match? */

		if (matched) {
			sed_cmd->in_match = !(
				/* has the ending line come, or is this a single address command? */
				(sed_cmd->end_line ?
					sed_cmd->end_line == -1 ?
						!next_line
						: (sed_cmd->end_line <= linenum)
					: !sed_cmd->end_match
				)
				/* or does this line matches our last address regex */
				|| (sed_cmd->end_match && old_matched
				     && (regexec(sed_cmd->end_match,
				    	         pattern_space, 0, NULL, 0) == 0))
			);
		}

		/* Skip blocks of commands we didn't match. */
		if (sed_cmd->cmd == '{') {
			if (sed_cmd->invert ? matched : !matched) {
				while (sed_cmd->cmd != '}') {
					sed_cmd = sed_cmd->next;
					if (!sed_cmd)
						bb_error_msg_and_die("unterminated {");
				}
			}
			continue;
		}

		/* Okay, so did this line match? */
		if (sed_cmd->invert ? !matched : matched) {
			/* Update last used regex in case a blank substitute BRE is found */
			if (sed_cmd->beg_match) {
				bbg.previous_regex_ptr = sed_cmd->beg_match;
			}

			/* actual sedding */
			switch (sed_cmd->cmd) {

			/* Print line number */
			case '=':
				fprintf(bbg.nonstdout, "%d\n", linenum);
				break;

			/* Write the current pattern space up to the first newline */
			case 'P':
			{
				char *tmp = strchr(pattern_space, '\n');

				if (tmp) {
					*tmp = '\0';
					/* TODO: explain why '\n' below */
					sed_puts(pattern_space, '\n');
					*tmp = '\n';
					break;
				}
				/* Fall Through */
			}

			/* Write the current pattern space to output */
			case 'p':
				/* NB: we print this _before_ the last line
				 * (of current file) is printed. Even if
				 * that line is nonterminated, we print
				 * '\n' here (gnu sed does the same) */
				sed_puts(pattern_space, '\n');
				break;
			/* Delete up through first newline */
			case 'D':
			{
				char *tmp = strchr(pattern_space, '\n');

				if (tmp) {
					tmp = xstrdup(tmp+1);
					free(pattern_space);
					pattern_space = tmp;
					goto restart;
				}
			}
			/* discard this line. */
			case 'd':
				goto discard_line;

			/* Substitute with regex */
			case 's':
				if (!do_subst_command(sed_cmd, &pattern_space))
					break;
				substituted |= 1;

				/* handle p option */
				if (sed_cmd->sub_p)
					sed_puts(pattern_space, last_gets_char);
				/* handle w option */
				if (sed_cmd->sw_file)
					puts_maybe_newline(
						pattern_space, sed_cmd->sw_file,
						&sed_cmd->sw_last_char, last_gets_char);
				break;

			/* Append line to linked list to be printed later */
			case 'a':
				append(sed_cmd->string);
				break;

			/* Insert text before this line */
			case 'i':
				sed_puts(sed_cmd->string, '\n');
				break;

			/* Cut and paste text (replace) */
			case 'c':
				/* Only triggers on last line of a matching range. */
				if (!sed_cmd->in_match)
					sed_puts(sed_cmd->string, NO_EOL_CHAR);
				goto discard_line;

			/* Read file, append contents to output */
			case 'r':
			{
				FILE *rfile;

				rfile = fopen(sed_cmd->string, "r");
				if (rfile) {
					char *line;

					while ((line = xmalloc_getline(rfile))
							!= NULL)
						append(line);
					xprint_and_close_file(rfile);
				}

				break;
			}

			/* Write pattern space to file. */
			case 'w':
				puts_maybe_newline(
					pattern_space, sed_cmd->sw_file,
					&sed_cmd->sw_last_char, last_gets_char);
				break;

			/* Read next line from input */
			case 'n':
				if (!bbg.be_quiet)
					sed_puts(pattern_space, last_gets_char);
				if (next_line) {
					free(pattern_space);
					pattern_space = next_line;
					last_gets_char = next_gets_char;
					next_line = get_next_line(&next_gets_char);
					linenum++;
					break;
				}
				/* fall through */

			/* Quit.  End of script, end of input. */
			case 'q':
				/* Exit the outer while loop */
				free(next_line);
				next_line = NULL;
				goto discard_commands;

			/* Append the next line to the current line */
			case 'N':
			{
				int len;
				/* If no next line, jump to end of script and exit. */
				if (next_line == NULL) {
					/* Jump to end of script and exit */
					free(next_line);
					next_line = NULL;
					goto discard_line;
				/* append next_line, read new next_line. */
				}
				len = strlen(pattern_space);
				pattern_space = realloc(pattern_space, len + strlen(next_line) + 2);
				pattern_space[len] = '\n';
				strcpy(pattern_space + len+1, next_line);
				last_gets_char = next_gets_char;
				next_line = get_next_line(&next_gets_char);
				linenum++;
				break;
			}

			/* Test/branch if substitution occurred */
			case 't':
				if (!substituted) break;
				substituted = 0;
				/* Fall through */
			/* Test/branch if substitution didn't occur */
			case 'T':
				if (substituted) break;
				/* Fall through */
			/* Branch to label */
			case 'b':
				if (!sed_cmd->string) goto discard_commands;
				else sed_cmd = branch_to(sed_cmd->string);
				break;
			/* Transliterate characters */
			case 'y':
			{
				int i, j;

				for (i = 0; pattern_space[i]; i++) {
					for (j = 0; sed_cmd->string[j]; j += 2) {
						if (pattern_space[i] == sed_cmd->string[j]) {
							pattern_space[i] = sed_cmd->string[j + 1];
							break;
						}
					}
				}

				break;
			}
			case 'g':	/* Replace pattern space with hold space */
				free(pattern_space);
				pattern_space = xstrdup(bbg.hold_space ? bbg.hold_space : "");
				break;
			case 'G':	/* Append newline and hold space to pattern space */
			{
				int pattern_space_size = 2;
				int hold_space_size = 0;

				if (pattern_space)
					pattern_space_size += strlen(pattern_space);
				if (bbg.hold_space)
					hold_space_size = strlen(bbg.hold_space);
				pattern_space = xrealloc(pattern_space,
						pattern_space_size + hold_space_size);
				if (pattern_space_size == 2)
					pattern_space[0] = 0;
				strcat(pattern_space, "\n");
				if (bbg.hold_space)
					strcat(pattern_space, bbg.hold_space);
				last_gets_char = '\n';

				break;
			}
			case 'h':	/* Replace hold space with pattern space */
				free(bbg.hold_space);
				bbg.hold_space = xstrdup(pattern_space);
				break;
			case 'H':	/* Append newline and pattern space to hold space */
			{
				int hold_space_size = 2;
				int pattern_space_size = 0;

				if (bbg.hold_space)
					hold_space_size += strlen(bbg.hold_space);
				if (pattern_space)
					pattern_space_size = strlen(pattern_space);
				bbg.hold_space = xrealloc(bbg.hold_space,
						hold_space_size + pattern_space_size);

				if (hold_space_size == 2)
					*bbg.hold_space = 0;
				strcat(bbg.hold_space, "\n");
				if (pattern_space)
					strcat(bbg.hold_space, pattern_space);

				break;
			}
			case 'x': /* Exchange hold and pattern space */
			{
				char *tmp = pattern_space;
				pattern_space = bbg.hold_space ? : xzalloc(1);
				last_gets_char = '\n';
				bbg.hold_space = tmp;
				break;
			}
			}
		}
	}

	/*
	 * exit point from sedding...
	 */
 discard_commands:
	/* we will print the line unless we were told to be quiet ('-n')
	   or if the line was suppressed (ala 'd'elete) */
	if (!bbg.be_quiet)
		sed_puts(pattern_space, last_gets_char);

	/* Delete and such jump here. */
 discard_line:
	flush_append();
	free(pattern_space);

	goto again;
}

/* It is possible to have a command line argument with embedded
   newlines.  This counts as multiple command lines. */

static void add_cmd_block(char *cmdstr)
{
	int go = 1;
	char *temp = xstrdup(cmdstr), *temp2 = temp;

	while (go) {
		int len = strcspn(temp2, "\n");
		if (!temp2[len]) go = 0;
		else temp2[len] = 0;
		add_cmd(temp2);
		temp2 += len+1;
	}
	free(temp);
}

static void add_cmds_link(llist_t *opt_e)
{
	if (!opt_e) return;
	add_cmds_link(opt_e->link);
	add_cmd_block(opt_e->data);
	free(opt_e);
}

static void add_files_link(llist_t *opt_f)
{
	char *line;
	FILE *cmdfile;
	if (!opt_f) return;
	add_files_link(opt_f->link);
	cmdfile = xfopen(opt_f->data, "r");
	while ((line = xmalloc_getline(cmdfile)) != NULL) {
		add_cmd(line);
		free(line);
	}
	xprint_and_close_file(cmdfile);
	free(opt_f);
}

int sed_main(int argc, char **argv)
{
	enum {
		OPT_in_place = 1 << 0,
	};
	unsigned opt;
	llist_t *opt_e, *opt_f;
	int status = EXIT_SUCCESS;

	bbg.sed_cmd_tail = &bbg.sed_cmd_head;

	/* destroy command strings on exit */
	if (ENABLE_FEATURE_CLEAN_UP) atexit(sed_free_and_close_stuff);

	/* Lie to autoconf when it starts asking stupid questions. */
	if (argc == 2 && !strcmp(argv[1], "--version")) {
		puts("This is not GNU sed version 4.0");
		return 0;
	}

	/* do normal option parsing */
	opt_e = opt_f = NULL;
	opt_complementary = "e::f::" /* can occur multiple times */
	                    "nn"; /* count -n */
	opt = getopt32(argc, argv, "irne:f:", &opt_e, &opt_f,
			    &bbg.be_quiet); /* counter for -n */
	argc -= optind;
	argv += optind;
	if (opt & OPT_in_place) { // -i
		atexit(cleanup_outname);
	}
	if (opt & 0x2) bbg.regex_type |= REG_EXTENDED; // -r
	//if (opt & 0x4) bbg.be_quiet++; // -n
	if (opt & 0x8) { // -e
		/* getopt32 reverses order of arguments, handle it */
		add_cmds_link(opt_e);
	}
	if (opt & 0x10) { // -f
		/* getopt32 reverses order of arguments, handle it */
		add_files_link(opt_f);
	}
	/* if we didn't get a pattern from -e or -f, use argv[0] */
	if (!(opt & 0x18)) {
		if (!argc)
			bb_show_usage();
		add_cmd_block(*argv++);
		argc--;
	}
	/* Flush any unfinished commands. */
	add_cmd("");

	/* By default, we write to stdout */
	bbg.nonstdout = stdout;

	/* argv[0..(argc-1)] should be names of file to process. If no
	 * files were specified or '-' was specified, take input from stdin.
	 * Otherwise, we process all the files specified. */
	if (argv[0] == NULL) {
		if (opt & OPT_in_place)
			bb_error_msg_and_die(bb_msg_requires_arg, "-i");
		add_input_file(stdin);
		process_files();
	} else {
		int i;
		FILE *file;

		for (i = 0; i < argc; i++) {
			struct stat statbuf;
			int nonstdoutfd;

			if (LONE_DASH(argv[i]) && !(opt & OPT_in_place)) {
				add_input_file(stdin);
				process_files();
				continue;
			}
			file = fopen_or_warn(argv[i], "r");
			if (!file) {
				status = EXIT_FAILURE;
				continue;
			}
			if (!(opt & OPT_in_place)) {
				add_input_file(file);
				continue;
			}

			bbg.outname = xasprintf("%sXXXXXX", argv[i]);
			nonstdoutfd = mkstemp(bbg.outname);
			if (-1 == nonstdoutfd)
				bb_error_msg_and_die("no temp file");
			bbg.nonstdout = fdopen(nonstdoutfd, "w");

			/* Set permissions of output file */

			fstat(fileno(file), &statbuf);
			fchmod(nonstdoutfd, statbuf.st_mode);
			add_input_file(file);
			process_files();
			fclose(bbg.nonstdout);

			bbg.nonstdout = stdout;
			/* unlink(argv[i]); */
			// FIXME: error check / message?
			rename(bbg.outname, argv[i]);
			free(bbg.outname);
			bbg.outname = 0;
		}
		if (bbg.input_file_count > bbg.current_input_file)
			process_files();
	}

	return status;
}