Hawk

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• Embedding Hawk in C Applications
• Embedding Hawk in C++ Applications
• Language
• Modules

Hawk is a powerful and embeddable scripting engine inspired by the traditional awk programming language. While it maintains compatibility with awk, Hawk is designed to be seamlessly integrated into other applications, providing a versatile and efficient solution for various scripting and data manipulation tasks.

As an embeddable interpreter, Hawk offers several advantages:

• Highly Portable: Implemented in portable C, Hawk can be easily integrated into applications running on diverse platforms and architectures.
• Efficient and Lightweight: With a focus on performance and minimalism, Hawk provides a lightweight yet capable scripting solution within larger applications.
• Extensible Architecture: Hawk features an extensible architecture, allowing developers to create and integrate custom extensions tailored to specific application requirements.

While mostly compatible with awk, Hawk introduces several enhancements and extensions, including:

• Improved Variable Handling: Enhanced mechanisms for working with complex data structures and performing advanced data manipulation.
• Additional Built-in Functions: A rich set of built-in functions that extend the capabilities of awk for string manipulation, array handling, and more.
• External Modules: Hawk supports external modules that provide additional functionality and extensibility.

Hawk's embeddable nature and extensible design make it a versatile choice for integrating scripting capabilities into a wide range of applications, from system utilities and tools to data processing pipelines and beyond.

In the following sections, we'll explore Hawk's features in detail, covering its embeddable nature, awk compatibility, extensions, and usage examples to help you effectively integrate and leverage this powerful scripting engine within your applications.

Embedding Hawk in C Applications

Here's an example of how Hawk can be embedded within a C application:

#include <hawk-std.h>
#include <stdio.h>
#include <string.h>

static const hawk_bch_t* src =
	"BEGIN {"
	"   for (i=2;i<=9;i++)"
	"   {"
	"       for (j=1;j<=9;j++)"
	"           print i \"*\" j \"=\" i * j;"
	"       print \"---------------------\";"
	"   }"
	"}";

int main ()
{
	hawk_t* hawk = HAWK_NULL;
	hawk_rtx_t* rtx = HAWK_NULL;
	hawk_val_t* retv;
	hawk_parsestd_t psin[2];
	int ret;

	hawk = hawk_openstd(0, HAWK_NULL); /* create a hawk instance */
	if (!hawk)
	{
		fprintf (stderr, "ERROR: cannot open hawk\n");
		ret = -1; goto oops;
	}

	/* set up source script file to read in */
	memset (&psin, 0, HAWK_SIZEOF(psin));
	psin[0].type = HAWK_PARSESTD_BCS;  /* specify the first script path */
	psin[0].u.bcs.ptr = (hawk_bch_t*)src;
	psin[0].u.bcs.len = hawk_count_bcstr(src);
	psin[1].type = HAWK_PARSESTD_NULL; /* indicate the no more script to read */

	ret = hawk_parsestd(hawk, psin, HAWK_NULL); /* parse the script */
	if (ret <= -1)
	{
		hawk_logbfmt (hawk, HAWK_LOG_STDERR, "ERROR(parse): %js\n", hawk_geterrmsg(hawk));
		ret = -1; goto oops;
	}

	/* create a runtime context needed for execution */
	rtx = hawk_rtx_openstd(
		hawk,
		0,
		HAWK_T("hawk02"),
		HAWK_NULL,  /* stdin */
		HAWK_NULL,  /* stdout */
		HAWK_NULL   /* default cmgr */
	);
	if (!rtx)
	{
		hawk_logbfmt (hawk, HAWK_LOG_STDERR, "ERROR(rtx_open): %js\n", hawk_geterrmsg(hawk));
		ret = -1; goto oops;
	}

	/* execute the BEGIN/pattern-action/END blocks */
	retv = hawk_rtx_loop(rtx); /* alternatively, hawk_rtx_exec(rtx, HAWK_NULL, 0) */
	if (!retv)
	{
		hawk_logbfmt (hawk, HAWK_LOG_STDERR, "ERROR(rtx_loop): %js\n", hawk_geterrmsg(hawk));
		ret = -1; goto oops;
	}

	/* lowered the reference count of the returned value */
	hawk_rtx_refdownval (rtx, retv);
	ret = 0;

oops:
	if (rtx) hawk_rtx_close (rtx); /* destroy the runtime context */
	if (hawk) hawk_close (hawk); /* destroy the hawk instance */
	return -1;
}

Embedding Hawk within an application involves a few key steps:

• Creating a Hawk Instance: The hawk_openstd() function is used to create a new instance of the Hawk interpreter, which serves as the entry point for interacting with Hawk from within the application.
• Parsing Scripts: The application can provide Hawk scripts as string literals or read them from files using the hawk_parsestd() function. This associates the scripts with the Hawk instance for execution.
• Creating a Runtime Context: A runtime context is created using hawk_rtx_openstd(), encapsulating the state and configuration required for script execution, such as input/output streams and other settings.
• Executing the Script: The hawk_rtx_loop() or hawk_rtx_exec() functions are used to execute the Hawk script within the created runtime context, returning a value representing the result of the execution.
• Handling the Result: The application can check the returned value for successful execution and handle any errors or results as needed.
• Cleaning Up: Finally, the application cleans up by closing the runtime context and destroying the Hawk instance using hawk_rtx_close() and hawk_close(), respectively.

By following this pattern, applications can seamlessly embed the Hawk interpreter, leveraging its scripting capabilities and data manipulation functionality while benefiting from its portability, efficiency, and extensibility.

Embedding Hawk in C++ Applications

Hawk can also be embedded in C++ applications. Here's an example:

#include <Hawk.hpp>
#include <stdio.h>

int main ()
{
	HAWK::HawkStd hawk;

	if (hawk.open() <= -1)
	{
		fprintf (stderr, "unable to open hawk - %s\n", hawk.getErrorMessageB());
		return -1;
	}

	HAWK::HawkStd::SourceString s("BEGIN { print \"hello, world\"; }");
	if (hawk.parse(s, HAWK::HawkStd::Source::NONE) == HAWK_NULL)
	{
		fprintf (stderr, "unable to parse - %s\n", hawk.getErrorMessageB());
		hawk.close ();
		return -1;
	}

	HAWK::Hawk::Value vr;
	hawk.loop (&vr);  // alternatively, hawk.exec (&vr, HAWK_NULL, 0);

	hawk.close ();
	return 0;
}

Embedding Hawk within a C++ application involves the following key steps:

• Creating a Hawk Instance: Create a new instance of the Hawk interpreter using the HAWK::HawkStd class.
• Parsing Scripts: Provide Hawk scripts as strings using the HAWK::HawkStd::SourceString class, and parse them using the hawk.parse() method.
• Executing the Script: Use the hawk.loop() or hawk.exec() methods to execute the Hawk script, returning a value representing the result of the execution.
• Handling the Result: Handle the returned value or any errors that occurred during execution.
• Cleaning Up: Clean up by calling hawk.close() to destroy the Hawk instance.

The C++ classes are inferior to the C equivalents in that they don't allow creation of multiple runtime contexts over a single hawk instance.

Language

Hawk is an AWK interpreter with many extended features implemented by its creator, with 'H' representing the initial of the creator's name. It aims to be an easy-to-embed implementation as well as a standalone tool.

At its core, Hawk largely supports all the fundamental features of AWK, ensuring compatibility with existing AWK programs and scripts, while introducing subtle differences in behavior, which will be explained in the incompatibility section. The following is an overview of the basic AWK features supported by Hawk:

1. Pattern-Action Statements: Hawk operates on a series of pattern-action statements. Each statement consists of a pattern that matches input records and an associated action that is executed when the pattern matches.
2. Record Processing: Hawk processes input data by splitting it into records and fields. Records are typically lines in a file, while fields are segments of each record separated by a field separator (by default, whitespace). This enables powerful text processing capabilities.
3. Built-in Variables: Hawk provides a set of built-in variables that facilitate data manipulation. Commonly used variables include NF (number of fields in the current record), NR (current record number), and $n (the value of the nth field in the current record).
4. Built-in Functions: Hawk offers a rich set of built-in functions to perform various operations on data. These functions include string manipulation, numeric calculations, regular expression matching, and more. You can harness their power to transform and analyze your input data effectively.
5. Output Formatting: Hawk provides flexible control over the formatting and presentation of output. You can customize the field and record separators, control the output field width, and apply formatting rules to align columns.

With these foundational features, Hawk ensures compatibility with existing AWK scripts and enables you to utilize the vast range of AWK resources available.

Entry Point

The typical execution begins with the BEGIN block, proceeds through pattern-action blocks, and concludes with the END block. If you would like to use a function as the entry point, you can specify a function name using @pragma entry.

@pragma entry main

function main ()
{
	print "hello, world";
}

Pragmas

Besides the entry pragma, there are other prgrmas available.

A pragma item of the file scope can be placed in any source files. A pragma item of the global scope can appear only once thoughout the all source files.

Name	Scope	Values	Description
implicit	file	on, off	allow undeclared variables
multilinestr	file	on, off	allow a multiline string literal without continuation
entry	global	function name	change the program entry point
striprecspc	global	on, off	trim leading and trailing spaces when convering a string to a number

@pragma implicit off
BEGIN {	a = 10; } ## syntax error - undefined identifier 'a'

@pragma implicit off
BEGIN {	@local a; a = 10; } # syntax ok - a is declared before use.

@include and @include_once

The @include directive inserts the contents of the file specified in the following string as if they appeared in the source stream being processed.

Assuming the hello.inc file contains the print_hello() function as shown below,

function print_hello() { print "hello\n"; }

You may include the the file and use the function.

@include "hello.inc";
BEGIN { print_hello(); }

The semicolon after the included file name is optional. You could write @include "hello.inc" without the ending semicolon.

@include_once is similar to @include except it doesn't include the same file multiple times.

@include_once "hello.inc";
@include_once "hello.inc";
BEGIN { print_hello(); }

In this example, print_hello() is not included twice.

You may use @include and @include_once inside a block as well as at the top level.

BEGIN {
	@include "init.inc";
	...
}

Comments

Hawk supports a single-line commnt that begins with a hash sign # and the C-style multi-line comment.

x = y; # assign y to x.
/*
this line is ignored.
this line is ignored too.
*/

Reserved Words

The following words are reserved and cannot be used as a variable name, a parameter name, or a function name.

• @abort
• @global
• @include
• @include_once
• @local
• @pragma
• @reset
• BEGIN
• END
• break
• continue
• delete
• do
• else
• exit
• for
• function
• getbline
• getline
• if
• in
• next
• nextfile
• nextofile
• print
• printf
• return
• while

However, these words can be used as normal names in the context of a module call. For example, mymod::break. In practice, the predefined names used for built-in commands, functions, and variables are treated as if they are reserved since you can't create another denifition with the same name.

Values

• unitialized value
• integer
• floating-point number
• string
• byte string
• array - light-weight array with numeric index only
• map - conventional AWK array
• function
• regular expression

To know the current type of a value, call hawk::typename().

function f() { return 10; }
BEGIN { 
	a="hello";
	b=12345;
	print hawk::typename(a), hawk::typename(b), hawk::typename(c), hawk::typename(f), hawk::typename(1.23), hawk::typename(B"world");
}

A regular expression literal is special in that it never appears as an indendent value and still entails a match operation against $0 without an match operator.

BEGIN { $0="ab"; print /ab/, hawk::typename(/ab/); }

For this reason, there is no way to get the type name of a regular expressin literal.

Numbers

An integer begins with a numeric digit between 0 and 9 inclusive and can be followed by more numeric digits. If an integer is immediately followed by a floating point, and optionally a series of numeric digits without whitespaces, it becomes a floting-point number. An integer or a simple floating-point number can be followed by e or E, and optionally a series of numeric digits with a optional single sign letter. A floating-point number may begin with a floting point with a preceeding number.

• 369 # integer
• 3.69 # floating-pointe number
• 13. # 13.0
• .369 # 0.369
• 34e-2 # 34 * (10 ** -2)
• 34e+2 # 34 * (10 ** 2)
• 34.56e # 34.56
• 34.56E3

An integer can be prefixed with 0x, 0, 0b for a hexa-decimal number, an octal number, and a binary number respectively. For a hexa-decimal number, letters from A to F can form a number case-insenstively in addition to numeric digits.

• 0xA1 # 161
• 0xB0b0 # 45232
• 020 # 16
• 0b101 # 5

If the prefix is not followed by any numeric digits, it is still a valid token and represents the value of 0.

• 0x # 0x0 but not desirable.
• 0b # 0b0 but not desirable.

Modules

Hawk supports various modules.

Hawk

• hawk::array
• hawk::call
• hawk::cmgr_exists
• hawk::function_exists
• hawk::gc
• hawk::gc_get_threshold
• hawk::gc_set_threshold
• hawk::gcrefs
• hawk::hash
• hawk::isarray
• hawk::ismap
• hawk::isnil
• hawk::map
• hawk::modlibdirs
• hawk::typename
• hawk::GC_NUM_GENS

String

The str module provides an extensive set of string manipulation functions.

• str::fromcharcode
• str::gsub - equivalent to gsub
• str::index
• str::isalnum
• str::isalpha
• str::isblank
• str::iscntrl
• str::isdigit
• str::isgraph
• str::islower
• str::isprint
• str::ispunct
• str::isspace
• str::isupper
• str::isxdigit
• str::length - equivalent to length
• str::ltrim
• str::match - similar to match. the optional third argument is the search start index. the optional fourth argument is equivalent to the thrid argument to match().
• str::normspace
• str::printf - equivalent to sprintf
• str::rindex
• str::rtrim
• str::split - equivalent to split
• str::sub - equivalent to sub
• str::substr - equivalent to substr
• str::tocharcode - get the numeric value of the first character
• str::tolower - equivalent to tolower
• str::tonum - convert a string to a number. a numeric value passed as a parameter is returned as it is. the leading prefix of 0b, 0, and 0x specifies the radix of 2, 8, 16 repectively. conversion stops when the end of the string is reached or the first invalid character for conversion is encountered.
• str::toupper - equivalent to toupper
• str::trim

System

The sys module provides various functions concerning the underlying operation system.

• sys::chmod
• sys::close
• sys::closedir
• sys::dup
• sys::errmsg
• sys::fork
• sys::getegid
• sys::getenv
• sys::geteuid
• sys::getgid
• sys::getpid
• sys::getppid
• sys::gettid
• sys::gettime
• sys::getuid
• sys::kill
• sys::mkdir
• sys::mktime
• sys::open
• sys::opendir
• sys::openfd
• sys::pipe
• sys::read
• sys::readdir
• sys::setttime
• sys::sleep
• sys::strftime
• sys::system
• sys::unlink
• sys::wait
• sys::write

You may read the file in raw bytes.

BEGIN {
	f = sys::open("/etc/sysctl.conf", sys::O_RDONLY);
	while (sys::read(f, x, 10) > 0) printf (B"%s", x);
	sys::close (f);
}

You can map a raw file descriptor to a handle created by this module and use it.

BEGIN {
	a = sys::openfd(1);
	sys::write (a, B"let me write something here\n");
	sys::close (a, sys::C_KEEPFD); ## set C_KEEPFD to release 1 without closing it.
	##sys::close (a);
	print "done\n";
}

Creating pipes and sharing them with a child process is not big an issue.

BEGIN {
	if (sys::pipe(p0, p1, sys::O_CLOEXEC | sys::O_NONBLOCK) <= -1)
	##if (sys::pipe(p0, p1, sys::O_CLOEXEC) <= -1)
	##if (sys::pipe(p0, p1) <= -1)
	{
		print "pipe error";
		return -1;
	}
	a = sys::fork();
	if (a <= -1) 
	{
		print "fork error";
		sys::close (p0);
		sys::close (p1);
	}
	else if (a == 0)
	{
		## child
		printf ("child.... %d %d %d\n", sys::getpid(), p0, p1);
		sys::close (p1);
		while (1)
		{
			n = sys::read (p0, k, 3);
			if (n <= 0) 
			{
				if (n == sys::RC_EAGAIN) continue; ## nonblock but data not available
				if (n != 0) print "ERROR: " sys::errmsg();
				break;
			}
			print k;
		}
		sys::close (p0);
		return 123;
	}
	else
	{
		## parent
		printf ("parent.... %d %d %d\n", sys::getpid(), p0, p1);
		sys::close (p0);
		sys::write (p1, B"hello");
		sys::write (p1, B"world");
		sys::close (p1);

		##sys::wait(a, status, sys::WNOHANG);
		while (sys::wait(a, status) != a);
		if (sys::WIFEXITED(status)) print "Exit code: " sys::WEXITSTATUS(status);
		else print "Child terminated abnormally"
	}
}

You can read standard output of a child process in a parent process.

BEGIN {
	if (sys::pipe(p0, p1, sys::O_NONBLOCK | sys::O_CLOEXEC) <= -1)
	{
			print "pipe error";
			return -1;
	}
	a = sys::fork();
	if (a <= -1)
	{
		print "fork error";
		sys::close (p0);
		sys::close (p1);
	}
	else if (a == 0)
	{
		## child
		sys::close (p0);

		stdout = sys::openfd(1);
		sys::dup(p1, stdout);

		print B"hello world";
		print B"testing sys::dup()";
		print B"writing to standard output..";

		sys::close (p1);
		sys::close (stdout);
	}
	else
	{
		sys::close (p1);
		while (1)
		{
			n = sys::read(p0, k, 10);
			if (n <= 0)
			{
				if (n == sys::RC_EAGAIN) continue; ## nonblock but data not available
				if (n != 0) print "ERROR: " sys::errmsg();
				break;
			}
			print "[" k "]";
		}
		sys::close (p0);
		sys::wait(a);
	}
}

You can duplicate file handles as necessary.

BEGIN {
	a = sys::open("/etc/inittab", sys::O_RDONLY);
	x = sys::open("/etc/fstab", sys::O_RDONLY);

	b = sys::dup(a);
	sys::close(a);

	while (sys::read(b, abc, 100) > 0) printf (B"%s", abc);

	print "-------------------------------";

	c = sys::dup(x, b, sys::O_CLOEXEC);
	## assertion: b == c
	sys::close (x);

	while (sys::read(c, abc, 100) > 0) printf (B"%s", abc);
	sys::close (c);
}

Directory traversal is easy.

BEGIN {
	d = sys::opendir("/etc", sys::DIR_SORT);
	if (d >= 0)
	{
		while (sys::readdir(d,a) > 0)
		{
			print a;
			sys::stat("/etc/" %% a, b);
			for (i in b) print "\t", i, b[i];
		}
		sys::closedir(d);
	} 
}

You can get information of a network interface.

BEGIN { 
	if (sys::getnwifcfg("lo", sys::NWIFCFG_IN6, x) <= -1)
		print sys::errmsg();
	else
		for (i in x) print i, x[i]; 
}

Socket functions are available.

BEGIN
{
	s = sys::socket();
	...
	sys::close (s);
}

ffi

• ffi::open
• ffi::close
• ffi::call
• ffi::errmsg

BEGIN {
	ffi = ffi::open();
	if (ffi::call(ffi, r, @B"getenv", @B"s>s", "PATH") <= -1) print ffi::errmsg();
	else print r;
	ffi::close (ffi);
}

mysql

BEGIN {
	mysql = mysql::open();

	if (mysql::connect(mysql, "localhost", "username", "password", "mysql") <= -1)
	{
			print "connect error -", mysql::errmsg();
	}

	if (mysql::query(mysql, "select * from user") <= -1)
	{
		print "query error -", mysql::errmsg();
	}

	result = mysql::store_result(mysql);
	if (result <= -1)
	{
		print "store result error - ", mysql::errmsg();
	}

	while (mysql::fetch_row(result, row) > 0)
	{
		ncols = length(row);
		for (i = 0; i < ncols; i++) print row[i];
		print "----";
	}

	mysql::free_result(result);

	mysql::close(mysql);
}

Incompatibility with AWK

Parameter passing

In AWK, it is possible for the caller to pass an uninitialized variable as a function parameter and obtain a modified value if the called function sets it to an array.

function q(a) {
  a[1] = 20;
  a[2] = 30;
}

BEGIN {
  q(x);
  for (i in x)
    print i, x[i];
}

In Hawk, to achieve the same effect, you can indicate call-by-reference by prefixing the parameter name with an ampersand (&).

function q(&a) {
  a[1] = 20;
  a[2] = 30;
}

BEGIN {
  q(x);
  for (i in x)
    print i, x[i];
}

Alternatively, you may create an array or a map before passing it to a function.

function q(a) {
  a[1] = 20;
  a[2] = 30;
}

BEGIN {
  x[3] = 99; delete (x[3]);  ## x = hawk::array() or x = hawk::map() also will do
  q(x);
  for (i in x)
    print i, x[i];
}

Positional variable expression

There are subtle differences in handling expressions for positional variables. In Hawk, many of the ambiguity issues can be resolved by enclosing the expression in parentheses.

Expression	HAWK	AWK
$++$++i	syntax error	OK
$(++$(++i))	OK	syntax error