Support sam's structural regular expression based command language

For those not familiar with sam(1) more information can be found at

 http://sam.cat-v.org/

For now sam commands can be entered from the vis prompt via :sam <cmd>

A command behaves differently depending on the mode in which it is issued:

 - in visual mode it behaves as if an implicit extract x command
   matching the current selection(s) would be preceding it. That is
   the command is executed once for each selection.

 - in normal mode:

    * if an address for the command was provided it is evaluated starting
      from the current cursor position(s) i.e. dot is set to the current
      cursor position.

    * if no address was supplied to the command then:

       + if multiple cursors exist, the command is executed once for every
         cursor with dot set to the current line of the cursor

       + otherwise if there is only 1 cursor then the command is executed
         with dot set to the whole file

The command syntax was slightly tweaked to accpet more terse commands.

  - When specifiying text or regular expressions the trailing delimiter can
    be elided if the meaning is unambigious.

  - If only an address is provided the print command will be executed.

  - The print command creates a selection matching its range.

  - In text entry \t inserts a literal tab character (sam only recognizes \n).

Hence the sam command ,x/pattern/ can be abbreviated to x/pattern

If a command is successful vis switches to normal mode (and hence removes
any selections), otherwise the editor is kept in visual mode. The print
command "fails" by definition.

6 files changed, 836 insertions, 1 deletions

diff --git a/LICENSE b/LICENSE
index 940bd69..7c79698 100644
--- a/LICENSE
+++ b/LICENSE
@@ -26,6 +26,9 @@ under terms compatible with the above ISC license:
  - libutf.[ch] originate from libutf a port of Plan 9's Unicode library
    to Unix and are MIT licensed
 
+ - sam.[ch] is based on Rob Pike's sam text editor for Plan 9.
+   Licensed under the Lucent Public License Version 1.02.
+
  - lexers/* the LPeg based lexers used for syntax highlighting are
    imported from the Scintillua project licensed under the MIT license
 
diff --git a/sam.c b/sam.c
new file mode 100644
index 0000000..8f3fc0d
--- /dev/null
+++ b/sam.c
@@ -0,0 +1,800 @@
+/*
+ * Heavily inspired (and partially based upon) Rob Pike's sam text editor
+ * for Plan 9. Licensed under the Lucent Public License Version 1.02.
+ *
+ *  Copyright © 2000-2009 Lucent Technologies
+ *  Copyright © 2016 Marc André Tanner <mat at brain-dump.org>
+ */
+#include <string.h>
+#include <stdio.h>
+#include "sam.h"
+#include "vis-core.h"
+#include "buffer.h"
+#include "text.h"
+#include "text-motions.h"
+#include "text-objects.h"
+#include "text-regex.h"
+#include "util.h"
+
+typedef struct Address Address;
+typedef struct Command Command;
+typedef struct CommandDef CommandDef;
+
+struct Address {
+	char type;      /* # (char) l (line) / ? . $ + - , ; * */
+	Regex *regex;   /* NULL denotes default for x, y, X, and Y commands */
+	size_t number;  /* line or character number */
+	Address *left;  /* left hand side of a compound address , ; */
+	Address *right; /* either right hand side of a compound address or next address */
+};
+
+struct Command {
+	char name;                /* "index" into command table */
+	Address *address;         /* range of text for command */
+	Regex *regex;             /* regex to match, used by x, y, g, v, X, Y */
+	char *text;               /* text to insert, used by i, a, c */
+	const CommandDef *cmddef; /* which command is this? */
+	int count;                /* command count if any */
+	char flag;                /* command specific flags */
+	Command *cmd;             /* target of x, y, g, v, X, Y, { */
+	Command *next;            /* next command in {} group */
+};
+
+struct CommandDef {
+	char name;
+	enum {
+		CMD_CMD           = 1 << 0, /* does the command take a sub/target command? */
+		CMD_REGEX         = 1 << 1, /* regex after command? */
+		CMD_REGEX_DEFAULT = 1 << 2, /* is the regex optional i.e. can we use a default? */
+		CMD_COUNT         = 1 << 3, /* does the command support a count as in s2/../? */
+		CMD_TEXT          = 1 << 4, /* does the command need a text to insert? */
+		CMD_ADDRESS_NONE  = 1 << 5, /* is it an error to specify an address for the command */
+		CMD_ADDRESS_ALL   = 1 << 6, /* if no address is given, use the whole file */
+		CMD_SHELL         = 1 << 7, /* command needs a shell command as argument */
+	} flags;
+	char defcmd;                        /* name of a default target command */
+	bool (*func)(Vis*, Win*, Command*, Filerange*); /* command imiplementation */
+};
+
+static bool cmd_insert(Vis*, Win*, Command*, Filerange*);
+static bool cmd_append(Vis*, Win*, Command*, Filerange*);
+static bool cmd_change(Vis*, Win*, Command*, Filerange*);
+static bool cmd_delete(Vis*, Win*, Command*, Filerange*);
+static bool cmd_guard(Vis*, Win*, Command*, Filerange*);
+static bool cmd_extract(Vis*, Win*, Command*, Filerange*);
+static bool cmd_select(Vis*, Win*, Command*, Filerange*);
+static bool cmd_print(Vis*, Win*, Command*, Filerange*);
+static bool cmd_files(Vis*, Win*, Command*, Filerange*);
+static bool cmd_shell(Vis*, Win*, Command*, Filerange*);
+static bool cmd_substitute(Vis*, Win*, Command*, Filerange*);
+
+static const CommandDef cmds[] = {
+	/* name, flags,                default command,  command        */
+	{ 'a', CMD_TEXT,                             0,  cmd_append     },
+	{ 'c', CMD_TEXT,                             0,  cmd_change     },
+	{ 'd', 0,                                    0,  cmd_delete     },
+	{ 'g', CMD_CMD|CMD_REGEX,                   'p', cmd_guard      },
+	{ 'i', CMD_TEXT,                             0,  cmd_insert     },
+	{ 'p', 0,                                    0,  cmd_print      },
+	{ 's', CMD_TEXT,                             0,  cmd_substitute },
+	{ 'v', CMD_CMD|CMD_REGEX,                   'p', cmd_guard      },
+	{ 'x', CMD_CMD|CMD_REGEX|CMD_REGEX_DEFAULT, 'p', cmd_extract    },
+	{ 'y', CMD_CMD|CMD_REGEX|CMD_REGEX_DEFAULT, 'p', cmd_extract    },
+	{ 'X', CMD_CMD|CMD_REGEX|CMD_REGEX_DEFAULT,  0,  cmd_files      },
+	{ 'Y', CMD_CMD|CMD_REGEX|CMD_REGEX_DEFAULT,  0,  cmd_files      },
+	{ '!', CMD_SHELL|CMD_ADDRESS_NONE,           0,  cmd_shell      },
+	{ '>', CMD_SHELL,                            0,  cmd_shell      },
+	{ '<', CMD_SHELL,                            0,  cmd_shell      },
+	{ '|', CMD_SHELL,                            0,  cmd_shell      },
+	{ 0 /* array terminator */                                      },
+};
+
+static const CommandDef cmds_internal[] = {
+	{ 's', 0,                                    0,  cmd_select     },
+	{ 0 /* array terminator */                                      },
+};
+
+const char *sam_error(enum SamError err) {
+	static const char *error_msg[] = {
+		[SAM_ERR_OK]              = "Success",
+		[SAM_ERR_MEMORY]          = "Out of memory",
+		[SAM_ERR_ADDRESS]         = "Bad address",
+		[SAM_ERR_NO_ADDRESS]      = "Command takes no address",
+		[SAM_ERR_UNMATCHED_BRACE] = "Unmatched `}'",
+		[SAM_ERR_REGEX]           = "Bad regular expression",
+		[SAM_ERR_TEXT]            = "Bad text",
+		[SAM_ERR_COMMAND]         = "Unknown command",
+		[SAM_ERR_EXECUTE]         = "Error executing command",
+	};
+
+	return err < LENGTH(error_msg) ? error_msg[err] : NULL;
+}
+
+static Address *address_new(void) {
+	return calloc(1, sizeof(Address));
+}
+
+static void address_free(Vis *vis, Address *addr) {
+	if (!addr)
+		return;
+	if (addr->regex != vis->search_pattern)
+		text_regex_free(addr->regex);
+	address_free(vis, addr->left);
+	address_free(vis, addr->right);
+	free(addr);
+}
+
+static void skip_spaces(const char **s) {
+	while (**s == ' ' || **s == '\t')
+		(*s)++;
+}
+
+static char *parse_delimited_text(const char **s) {
+	Buffer buf;
+	bool escaped = false;
+	char delim = **s;
+
+	buffer_init(&buf);
+
+	for ((*s)++; **s && (**s != delim || escaped); (*s)++) {
+		if (!escaped && **s == '\\') {
+			escaped = true;
+			continue;
+		}
+
+		char c = **s;
+
+		if (escaped) {
+			escaped = false;
+			switch (**s) {
+			case '\n':
+				continue;
+			case 'n':
+				c = '\n';
+				break;
+			case 't':
+				c = '\t';
+				break;
+			}
+		}
+
+		if (!buffer_append(&buf, &c, 1)) {
+			buffer_release(&buf);
+			return NULL;
+		}
+	}
+
+	if (**s == delim)
+		(*s)++;
+
+	if (!buffer_append(&buf, "\0", 1)) {
+		buffer_release(&buf);
+		return NULL;
+	}
+
+	return buf.data;
+}
+
+static char *parse_text(const char **s) {
+	skip_spaces(s);
+	if (**s != '\n')
+		return parse_delimited_text(s);
+
+	Buffer buf;
+	buffer_init(&buf);
+	const char *start = *s + 1;
+	bool dot = false;
+
+	for ((*s)++; **s && (!dot || **s != '\n'); (*s)++)
+		dot = (**s == '.');
+
+	if (!dot || !buffer_put(&buf, start, *s - start - 1) ||
+	    !buffer_append(&buf, "\0", 1)) {
+		buffer_release(&buf);
+		return NULL;
+	}
+
+	return buf.data;
+}
+
+static Regex *parse_regex(Vis *vis, const char **s) {
+	Buffer buf;
+	bool escaped = false;
+	char delim = **s;
+	buffer_init(&buf);
+
+	for ((*s)++; **s && (**s != delim || escaped); (*s)++) {
+		if (!escaped && **s == '\\') {
+			escaped = true;
+			continue;
+		}
+		if (escaped) {
+			escaped = false;
+			if (**s != delim)
+				buffer_append(&buf, "\\", 1);
+		}
+		if (!buffer_append(&buf, *s, 1)) {
+			buffer_release(&buf);
+			return NULL;
+		}
+	}
+
+	buffer_append(&buf, "\0", 1);
+
+	Regex *regex = NULL;
+
+	if (**s == delim || **s == '\0') {
+		if (**s == delim)
+			(*s)++;
+		if (buffer_length0(&buf) == 0) {
+			regex = vis->search_pattern;
+		} else if ((regex = text_regex_new())) {
+			if (text_regex_compile(regex, buf.data, REG_EXTENDED|REG_NEWLINE) != 0) {
+				text_regex_free(regex);
+				regex = NULL;
+			} else {
+				text_regex_free(vis->search_pattern);
+				vis->search_pattern = regex;
+			}
+		}
+	}
+
+	buffer_release(&buf);
+	return regex;
+}
+
+static int parse_number(const char **s) {
+	char *end = NULL;
+	int number = strtoull(*s, &end, 10);
+	if (end == *s)
+		return 1;
+	*s = end;
+	return number;
+}
+
+static Address *address_parse_simple(Vis *vis, const char **s, enum SamError *err) {
+
+	skip_spaces(s);
+
+	Address addr = {
+		.type = **s,
+		.regex = NULL,
+		.number = 0,
+		.left = NULL,
+		.right = NULL,
+	};
+
+	switch (addr.type) {
+	case '#': /* character #n */
+		(*s)++;
+		addr.number = parse_number(s);
+		break;
+	case '0': case '1': case '2': case '3': case '4': /* line n */
+	case '5': case '6': case '7': case '8': case '9':
+		addr.type = 'l';
+		addr.number = parse_number(s);
+		break;
+	case '/': /* regexp forwards */
+	case '?': /* regexp backwards */
+		addr.regex = parse_regex(vis, s);
+		if (!addr.regex) {
+			*err = SAM_ERR_REGEX;
+			return NULL;
+		}
+		break;
+	case '$': /* end of file */
+	case '.':
+	case '+':
+	case '-':
+		(*s)++;
+		break;
+	default:
+		return NULL;
+	}
+
+	if ((addr.right = address_parse_simple(vis, s, err))) {
+		switch (addr.right->type) {
+		case '.':
+		case '$':
+			return NULL;
+		case '#':
+		case 'l':
+		case '/':
+		case '?':
+			if (addr.type != '+' && addr.type != '-') {
+				Address *plus = address_new();
+				if (!plus) {
+					address_free(vis, addr.right);
+					return NULL;
+				}
+				plus->type = '+';
+				plus->right = addr.right;
+				addr.right = plus;
+			}
+			break;
+		}
+	}
+
+	Address *ret = address_new();
+	if (!ret) {
+		address_free(vis, addr.right);
+		return NULL;
+	}
+	*ret = addr;
+	return ret;
+}
+
+static Address *address_parse_compound(Vis *vis, const char **s, enum SamError *err) {
+	Address addr = { 0 }, *left = address_parse_simple(vis, s, err), *right = NULL;
+	if (!left)
+		return NULL;
+	skip_spaces(s);
+	addr.type = **s;
+	switch (addr.type) {
+	case ',': /* a1,a2 */
+	case ';': /* a1;a2 */
+		(*s)++;
+		right = address_parse_compound(vis, s, err);
+		if (!right || ((right->type == ',' || right->type == ';') && !right->left)) {
+			if (right)
+				*err = SAM_ERR_ADDRESS;
+			goto fail;
+		}
+		break;
+	default:
+		return left;
+	}
+
+	addr.left = left;
+	addr.right = right;
+
+	Address *ret = address_new();
+	if (ret) {
+		*ret = addr;
+		return ret;
+	}
+
+fail:
+	address_free(vis, left);
+	address_free(vis, right);
+	return NULL;
+}
+
+static Command *command_new(void) {
+	return calloc(1, sizeof(Command));
+}
+
+static void command_free(Vis *vis, Command *cmd) {
+	if (!cmd)
+		return;
+
+	for (Command *c = cmd->cmd, *next; c; c = next) {
+		next = c->next;
+		command_free(vis, c);
+	}
+
+	address_free(vis, cmd->address);
+	if (cmd->regex != vis->search_pattern)
+		text_regex_free(cmd->regex);
+	free(cmd->text);
+	free(cmd);
+}
+
+static const CommandDef *command_lookup(const CommandDef *cmds, char name) {
+	if (!name)
+		name = 'p';
+	for (const CommandDef *cmd = cmds; cmd->name; cmd++) {
+		if (cmd->name == name)
+			return cmd;
+	}
+	return NULL;
+}
+
+static Command *command_parse(Vis *vis, const char **s, int level, enum SamError *err) {
+	Command *cmd = command_new();
+	if (!cmd)
+		return NULL;
+
+	cmd->address = address_parse_compound(vis, s, err);
+	skip_spaces(s);
+
+	cmd->name = **s;
+
+	const CommandDef *cmddef = command_lookup(cmds, cmd->name);
+
+	if (!cmddef) {
+		/* let it point to an all zero dummy entry */
+		cmddef = &cmds_internal[LENGTH(cmds_internal)-1];
+		switch (cmd->name) {
+		case '{':
+		{
+			(*s)++;
+			Command *prev = NULL, *next;
+			do {
+				skip_spaces(s);
+				if (**s == '\n')
+					(*s)++;
+				next = command_parse(vis, s, level+1, err);
+				if (prev)
+					prev->next = next;
+				else
+					cmd->cmd = next;
+			} while ((prev = next));
+			break;
+		}
+		case '}':
+			if (level == 0) {
+				*err = SAM_ERR_UNMATCHED_BRACE;
+				goto fail;
+			}
+			(*s)++;
+			command_free(vis, cmd);
+			return NULL;
+		default:
+			*err = SAM_ERR_COMMAND;
+			goto fail;
+		}
+	}
+
+	cmd->cmddef = cmddef;
+
+	(*s)++; /* skip command name */
+
+	if (cmddef->flags & CMD_ADDRESS_NONE && cmd->address) {
+		*err = SAM_ERR_NO_ADDRESS;
+		goto fail;
+	}
+
+	if (cmddef->flags & CMD_COUNT)
+		cmd->count = parse_number(s);
+
+	if (cmddef->flags & CMD_REGEX) {
+		if (cmddef->flags & CMD_REGEX_DEFAULT && **s == ' ') {
+			skip_spaces(s);
+		} else if (!(cmd->regex = parse_regex(vis, s))) {
+			*err = SAM_ERR_REGEX;
+			goto fail;
+		}
+	}
+
+	if (cmddef->flags & CMD_TEXT && !(cmd->text = parse_text(s))) {
+		*err = SAM_ERR_TEXT;
+		goto fail;
+	}
+
+	if (cmddef->flags & CMD_CMD) {
+		skip_spaces(s);
+		if (cmddef->defcmd && (**s == '\n' || **s == '\0')) {
+			if (**s == '\n')
+				(*s)++;
+			if (!(cmd->cmd = command_new()))
+				goto fail;
+			cmd->cmd->name = cmddef->defcmd;
+			cmd->cmd->cmddef = command_lookup(cmds, cmddef->defcmd);
+		} else {
+			if (!(cmd->cmd = command_parse(vis, s, level, err)))
+				goto fail;
+			if (cmd->name == 'X' || cmd->name == 'Y') {
+				Command *sel = command_new();
+				if (!sel)
+					goto fail;
+				sel->cmd = cmd->cmd;
+				sel->cmddef = command_lookup(cmds_internal, 's');
+				cmd->cmd = sel;
+			}
+		}
+	}
+
+	if (!cmd->address) {
+		if (cmddef->flags & CMD_ADDRESS_ALL) {
+			if (!(cmd->address = address_new()))
+				goto fail;
+			cmd->address->type = '*';
+		}
+	}
+
+	return cmd;
+fail:
+	command_free(vis, cmd);
+	return NULL;
+}
+
+static Command *sam_parse(Vis *vis, const char *cmd, enum SamError *err) {
+	const char **s = &cmd;
+	Command *c = command_parse(vis, s, 0, err);
+	if (!c)
+		return NULL;
+	Command *sel = command_new();
+	if (!sel) {
+		command_free(vis, c);
+		return NULL;
+	}
+	sel->cmd = c;
+	sel->cmddef = command_lookup(cmds_internal, 's');
+	return sel;
+}
+
+static Filerange address_line_evaluate(Address *addr, File *file, Filerange *range, int sign) {
+	size_t offset = addr->number != 0 ? addr->number : 1;
+	size_t line;
+	if (sign > 0) {
+		line = text_lineno_by_pos(file->text, range->end);
+		line = text_pos_by_lineno(file->text, line + offset);
+	} else if (sign < 0) {
+		line = text_lineno_by_pos(file->text, range->start);
+		line = offset < line ? text_pos_by_lineno(file->text, line - offset) : 0;
+	} else {
+		line = text_pos_by_lineno(file->text, addr->number);
+	}
+	return text_range_new(line, text_line_next(file->text, line));
+}
+
+static Filerange address_evaluate(Address *addr, File *file, Filerange *range, int sign) {
+	Filerange ret = text_range_empty();
+
+	do {
+		switch (addr->type) {
+		case '#':
+			if (sign > 0)
+				ret.start = ret.end = range->end + addr->number;
+			else if (sign < 0)
+				ret.start = ret.end = range->start - addr->number;
+			else
+				ret = text_range_new(addr->number, addr->number);
+			break;
+		case 'l':
+			ret = address_line_evaluate(addr, file, range, sign);
+			break;
+		case '?':
+			sign = sign == 0 ? -1 : -sign;
+			/* fall through */
+		case '/':
+			if (sign >= 0)
+				ret = text_object_search_forward(file->text, range->end, addr->regex);
+			else
+				ret = text_object_search_backward(file->text, range->start, addr->regex);
+			break;
+		case '$':
+		{
+			size_t size = text_size(file->text);
+			ret = text_range_new(size, size);
+			break;
+		}
+		case '.':
+			ret = *range;
+			break;
+		case '+':
+		case '-':
+			sign = addr->type == '+' ? +1 : -1;
+			if (!addr->right || addr->right->type == '+' || addr->right->type == '-')
+				ret = address_line_evaluate(addr, file, range, sign);
+			break;
+		case ',':
+		case ';':
+		{
+			Filerange left, right;
+			if (addr->left)
+				left = address_evaluate(addr->left, file, range, 0);
+			else
+				left = text_range_new(0, 0);
+
+			if (addr->type == ';')
+				range = &left;
+
+			if (addr->right) {
+				right = address_evaluate(addr->right, file, range, 0);
+			} else {
+				size_t size = text_size(file->text);
+				right = text_range_new(size, size);
+			}
+			/* TODO: enforce strict ordering? */
+			return text_range_union(&left, &right);
+		}
+		case '*':
+			return text_range_new(0, text_size(file->text));
+		}
+		if (text_range_valid(&ret))
+			range = &ret;
+	} while ((addr = addr->right));
+
+	return ret;
+}
+
+static bool sam_execute(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	bool ret = true;
+	Filerange r = cmd->address ? address_evaluate(cmd->address, win->file, range, 0) : *range;
+
+	switch (cmd->name) {
+	case '{':
+	{
+		Text *txt = win->file->text;
+		Mark start, end;
+		Filerange group = r;
+
+		for (Command *c = cmd->cmd; c; c = c->next) {
+			if (!text_range_valid(&group))
+				return false;
+
+			start = text_mark_set(txt, group.start);
+			end = text_mark_set(txt, group.end);
+
+			ret &= sam_execute(vis, win, c, &group);
+
+			size_t s = text_mark_get(txt, start);
+			/* hack to make delete work, only update if still valid */
+			if (s != EPOS)
+				group.start = s;
+			group.end = text_mark_get(txt, end);
+		}
+		break;
+	}
+	default:
+		ret = cmd->cmddef->func(vis, win, cmd, &r);
+		break;
+	}
+	return ret;
+}
+
+enum SamError sam_cmd(Vis *vis, const char *s) {
+	enum SamError err = SAM_ERR_OK;
+	Command *cmd = sam_parse(vis, s, &err);
+	if (!cmd) {
+		if (err == SAM_ERR_OK)
+			err = SAM_ERR_MEMORY;
+		return err;
+	}
+	Filerange range = text_range_empty();
+	bool status = sam_execute(vis, vis->win, cmd, &range);
+	vis_mode_switch(vis, status ? VIS_MODE_NORMAL : VIS_MODE_VISUAL);
+	command_free(vis, cmd);
+	return err;
+}
+
+static bool cmd_insert(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	size_t len = strlen(cmd->text);
+	bool ret = text_insert(win->file->text, range->start, cmd->text, len);
+	if (ret)
+		*range = text_range_new(range->start, range->start + len);
+	return ret;
+}
+
+static bool cmd_append(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	size_t len = strlen(cmd->text);
+	bool ret = text_insert(win->file->text, range->end, cmd->text, len);
+	if (ret)
+		*range = text_range_new(range->end, range->end + len);
+	return ret;
+}
+
+static bool cmd_change(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	Text *txt = win->file->text;
+	size_t len = strlen(cmd->text);
+	bool ret = text_delete(txt, range->start, text_range_size(range)) &&
+	      text_insert(txt, range->start, cmd->text, len);
+	if (ret)
+		*range = text_range_new(range->start, range->start + len);
+	return ret;
+}
+
+static bool cmd_delete(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	bool ret = text_delete(win->file->text, range->start, text_range_size(range));
+	if (ret)
+		*range = text_range_new(range->start, range->start);
+	return ret;
+}
+
+static bool cmd_guard(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	bool match = !text_search_range_forward(win->file->text, range->start,
+		text_range_size(range), cmd->regex, 0, NULL, 0);
+	if (match ^ (cmd->name == 'v'))
+		return sam_execute(vis, win, cmd->cmd, range);
+	return true;
+}
+
+static bool cmd_extract(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	bool ret = true;
+	Text *txt = win->file->text;
+	if (cmd->regex) {
+		size_t start = range->start, end = range->end;
+		RegexMatch match[1];
+		while (start < end) {
+			bool found = text_search_range_forward(txt, start,
+				end - start, cmd->regex, 1, match, 0) == 0 &&
+				match[0].start != match[0].end;
+			Filerange r = text_range_empty();
+			if (found) {
+				if (cmd->name == 'x')
+					r = text_range_new(match[0].start, match[0].end);
+				else
+					r = text_range_new(start, match[0].start);
+				start = match[0].end;
+			} else {
+				if (cmd->name == 'y')
+					r = text_range_new(start, end);
+				start = end;
+			}
+
+			if (text_range_valid(&r) && r.start != r.end) {
+				Mark mark_start = text_mark_set(txt, start);
+				Mark mark_end = text_mark_set(txt, end);
+				ret &= sam_execute(vis, win, cmd->cmd, &r);
+				start = text_mark_get(txt, mark_start);
+				end = text_mark_get(txt, mark_end);
+				if (start == EPOS || end == EPOS)
+					return false;
+			}
+		}
+	} else {
+		size_t start = range->start;
+		for (;;) {
+			size_t end = text_line_next(txt, start);
+			Filerange line = text_range_new(start, end);
+			if (start == end || !text_range_valid(&line))
+				break;
+			Mark mark_end = text_mark_set(txt, end);
+			ret &= sam_execute(vis, win, cmd->cmd, &line);
+			start = text_mark_get(txt, mark_end);
+			if (start == EPOS)
+				return false;
+		}
+	}
+	return ret;
+}
+
+static bool cmd_select(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	bool ret = true;
+	View *view = win->view;
+	Text *txt = win->file->text;
+	bool multiple_cursors = view_cursors_count(view) > 1;
+	for (Cursor *c = view_cursors(view), *next; c; c = next) {
+		next = view_cursors_next(c);
+		Filerange sel;
+		if (vis->mode->visual) {
+			sel = view_cursors_selection_get(c);
+		} else if (cmd->cmd->address) {
+			size_t start = view_cursors_pos(c);
+			size_t end = text_char_next(txt, start);
+			sel = text_range_new(start, end);
+		} else if (multiple_cursors) {
+			sel = text_object_line(txt, view_cursors_pos(c));
+		} else {
+			sel = text_range_new(0, text_size(txt));
+		}
+		ret &= sam_execute(vis, win, cmd->cmd, &sel);
+		view_cursors_dispose(c);
+	}
+	return ret;
+}
+
+static bool cmd_print(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	View *view = win->view;
+	Text *txt = win->file->text;
+	Cursor *cursor = view_cursors_new(view);
+	if (cursor) {
+		view_cursors_selection_set(cursor, range);
+		view_cursors_to(cursor, text_char_prev(txt, range->end));
+	}
+	/* indicate "failure"/incomplete command to keep visual mode */
+	return false;
+}
+
+static bool cmd_files(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	bool ret = true;
+	for (Win *win = vis->windows; win; win = win->next) {
+		if (win->file->internal)
+			continue;
+		bool match = !cmd->regex || (win->file->name &&
+		             text_regex_match(cmd->regex, win->file->name, 0));
+		if (match ^ (cmd->name == 'Y'))
+			ret &= sam_execute(vis, win, cmd->cmd, range);
+	}
+	return ret;
+}
+
+static bool cmd_shell(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	return false;
+}
+
+static bool cmd_substitute(Vis *vis, Win *win, Command *cmd, Filerange *range) {
+	return false;
+}
diff --git a/sam.h b/sam.h
new file mode 100644
index 0000000..fb4f314
--- /dev/null
+++ b/sam.h
@@ -0,0 +1,21 @@
+#ifndef SAM_H
+#define SAM_H
+
+#include "vis.h"
+
+enum SamError {
+	SAM_ERR_OK,
+	SAM_ERR_MEMORY,
+	SAM_ERR_ADDRESS,
+	SAM_ERR_NO_ADDRESS,
+	SAM_ERR_UNMATCHED_BRACE,
+	SAM_ERR_REGEX,
+	SAM_ERR_TEXT,
+	SAM_ERR_COMMAND,
+	SAM_ERR_EXECUTE,
+};
+
+enum SamError sam_cmd(Vis *vis, const char *cmd);
+const char *sam_error(enum SamError);
+
+#endif
diff --git a/text-regex.h b/text-regex.h
index 15b2340..c18caa3 100644
--- a/text-regex.h
+++ b/text-regex.h
@@ -1,6 +1,7 @@
 #ifndef TEXT_REGEX_H
 #define TEXT_REGEX_H
 
+#include <regex.h>
 #include "text.h"
 
 typedef struct Regex Regex;
diff --git a/vis-cmds.c b/vis-cmds.c
index bb90e35..9365d4e 100644
--- a/vis-cmds.c
+++ b/vis-cmds.c
@@ -16,6 +16,7 @@
 #include "text-motions.h"
 #include "text-objects.h"
 #include "util.h"
+#include "sam.h"
 
 enum CmdOpt {          /* option flags for command definitions */
 	CMD_OPT_NONE,  /* no option (default value) */
@@ -91,6 +92,7 @@ static bool cmd_map(Vis*, Filerange*, enum CmdOpt, const char *argv[]);
 static bool cmd_unmap(Vis*, Filerange*, enum CmdOpt, const char *argv[]);
 /* set language specific key bindings */
 static bool cmd_langmap(Vis*, Filerange*, enum CmdOpt, const char *argv[]);
+static bool cmd_sam(Vis*, Filerange*, enum CmdOpt, const char *argv[]);
 
 /* command recognized at the ':'-prompt. commands are found using a unique
  * prefix match. that is if a command should be available under an abbreviation
@@ -124,6 +126,7 @@ static const Command cmds[] = {
 	{ { "later"                    }, cmd_earlier_later, CMD_OPT_NONE               },
 	{ { "!",                       }, cmd_filter,        CMD_OPT_NONE               },
 	{ { "|",                       }, cmd_pipe,          CMD_OPT_NONE               },
+	{ { "sam"                      }, cmd_sam,           CMD_OPT_NONE               },
 	{ { NULL,                      }, NULL,              CMD_OPT_NONE               },
 };
 
@@ -1152,6 +1155,13 @@ static bool cmd_unmap(Vis *vis, Filerange *range, enum CmdOpt opt, const char *a
 		return vis_mode_unmap(vis, mode, lhs);
 }
 
+static bool cmd_sam(Vis *vis, Filerange *range, enum CmdOpt opt, const char *argv[]) {
+	enum SamError err = sam_cmd(vis, argv[1]);
+	if (err != SAM_ERR_OK)
+		vis_info_show(vis, "%s", sam_error(err));
+	return err == SAM_ERR_OK;
+}
+
 static Filepos parse_pos(Win *win, char **cmd) {
 	size_t pos = EPOS;
 	View *view = win->view;
diff --git a/vis-prompt.c b/vis-prompt.c
index d051762..52a0fbd 100644
--- a/vis-prompt.c
+++ b/vis-prompt.c
@@ -17,7 +17,7 @@ bool vis_prompt_cmd(Vis *vis, const char *cmd) {
 		register_put0(vis, &vis->registers[VIS_REG_COMMAND], cmd+1);
 		bool ret = vis_cmd(vis, cmd+1);
 		if (ret && vis->mode->visual)
-			vis_mode_switch(vis, VIS_MODE_NORMAL);
+			;//vis_mode_switch(vis, VIS_MODE_NORMAL);
 		return ret;
 	}
 	default: