# Hawk

	█░█ ▄▀█ █░█░█ █▄▀
	█▀█ █▀█ ▀▄▀▄▀ █░█

 - [Language](#language)
 - [Modules](#modules)
 - [Embedding Guide](#embedding-guide)

## Language <a name="language"></a>

Hawk is an AWK interpreter with many extended features implemetned by who 'H' 
stands for. It aims to be an easy-to-embed implementation as well as used
standalone.

### Program Structure

A Hawk program is composed of the following elements at the top level.

 - pattern-action block pair
   - BEGIN action block pair
   - END action block pair
   - action block without a pattern
   - pattern without an action block
 - user-defined function
 - @global variable declaration
 - @include directive
 - @pragma directive

However, none of the above is mandatory. Hawk accepts an empty program.

### Pattern-Action Block Pair

A pattern-action pair is composed of a pattern and an action block as shown below:

	pattern {
		statement
		statement
		...
	}

A pattern can be one of the followings when specified:

 - expression
 - first-expression, last-expression
 - *BEGIN*
 - *END*

An action block is a series of statements enclosed in a curly bracket pair. The *BEGIN* and *END* patterns require an action block while normal patterns don't. When no action block is specified for a normal pattern, it is treated
as if `{ print $0; }` is specified.

Hawk executes the action block for the *BEGIN* pattern when it starts executing a program; No start-up action is taken if no *BEGIN* pattern-action pair is specified. If a normal pattern-action pair and/or the *END* 
pattern-action is specified, it reads the standard input stream. For each input line it reads, it checks if a normal pattern expression evaluates to true. For each pattern that evaluates to true, it executes the action block specified for
the pattern. When it reaches the end of the input stream, it executes the action block for the *END* pattern.

Hawk allows zero or more *BEGIN* patterns. When multiple *BEGIN* patterns are specified, it executes their action blocks in their appearance order in the program. The same applies to the *END* patterns and their action blocks. It 
doesn't read the standard input stream for programs composed of BEGIN blocks only whereas it reads the stream as long as there is an action block for the END pattern or a normal pattern. It evaluates an empty pattern to true;
As a result, the action block for an empty pattern is executed for all input lines read.

You can compose a pattern range by putting 2 patterns separated by a comma. The pattern range evaluates to true once the first expression evaluates to true until the last expression evaluates to true.

The following code snippet is a valid Hawk program that prints the string *hello, world* to the console and exits.


	BEGIN {
		print "hello, world";
	}

This program prints "hello, world" followed by "hello, all" to the console.

	BEGIN {
		print "hello, world";
	}
	BEGIN {
		print "hello, all";
	}

For the following text input,

	abcdefgahijklmn
	1234567890
	opqrstuvwxyzabc
	9876543210

this program

	BEGIN { mr=0; my_nr=0; }
	/abc/ { print "[" $0 "]"; mr++; }
	{ my_nr++; }
	END { 
		print "total records: " NR; 
		print "total records selfcounted: " my_nr; 
		print "matching records: " mr; 
	}

produces the output text like this:

	[abcdefgahijklmn]
	[opqrstuvwxyzabc]
	total records: 4
	total records selfcounted: 4
	matching records: 2

See the table for the order of execution indicated by the number and the result 
of pattern evaluation enclosed in parenthesis. The action block is executed if
the evaluation result is true.

|                                     | START-UP | abcdefgahijklmn | 1234567890 | opqrstuvwxyzabc | 9876543210 | SHUTDOWN |
|-------------------------------------|----------|-----------------|------------|-----------------|------------|----------|
| `BEGIN { mr = 0; my_nr=0; }`        | 1(true)  |                 |            |                 |            |          |
| `/abc/ { print "[" $0 "]"; mr++; }` |          | 2(true)         | 4(false)   | 6(true)         | 8(false)   |          |
| `{ my_nr++; }`                      |          | 3(true)         | 5(true)    | 7(true)         | 9(true)    |          |
| `END { print ... }`                 |          |                 |            |                 |            | 10(true) | 

For the same input, this program shows how to use a ranged pattern.

	/abc/,/stu/ { print "[" $0 "]"; }

It produces the output text like this:

	[abcdefgahijklmn]
	[1234567890]
	[opqrstuvwxyzabc]

The regular expression `/abc/` matches the first input line and `/stu/` matches the
third input line. So the range is true between the first input line and the
third input line inclusive.


### Entry Point

The typical execution begins with the BEGIN block, goes through pattern-action blocks, and eaches the END block. If you like to use a function as an entry point, you may set a function name with @pragma entry.

	@pragma entry main

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


### Pragmas

Besides the entry pragma, there are other prgrma 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       |                                                        |
| striprecspc   | global | on, off       | trim leading and trailing spaces when convering a string to a number |



### @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
- function
- regular expression

To know the current type of a value, call 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/, 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 <a name="modules"></a>

Hawk supports various modules.


#### 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 - equivalent 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


### 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, the caller can pass an uninitialized variable as a function parameter and get a changed value if the callled 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, you can prefix the pramater name with & to indicate call-by-reference for the same effect.

	function q(&a) {a[1]=20; a[2]=30;}
	BEGIN { q(x); for (i in x) print i, x[i]; }


Alternatively, you may form an array before passing it to a function.

	function q(a) {a[1]=20; a[2]=30;}
	BEGIN { x[3]=99; q(x); for (i in x) print i, x[i]; }'


### Positional variable expression

There are subtle differences when you put an expression for a position variable. In Hawk, most of the ambiguity issues are resolved if you enclose the expression inside parentheses.

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


## Embedding Guide <a name="embedding-guide"></a>

To use hawk in your program, do the followings:

- create a hawk instance
- parse a source script
- create a runtime context
- trigger execution on the runtime context
- destroy the runtime context
- destroy the hawk instance

The following sample illustrates the basic steps hightlighed above.

	#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);
		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;
	}


If you prefer C++, you may use the Hawk/HawkStd wrapper classes to simplify the task. 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. Here is the sample code that prints "hello, world".

	#include <HawkStd.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.exec (&vr, HAWK_NULL, 0);
	
		hawk.close ();
		return 0;
	}
