Hawk

• Hawk
• Building Hawk From Source Code
• Embedding Hawk in C Applications
• Embedding Hawk in C++ Applications
• Language
  • Pragmas
    • @pragma entry
    • @pragma implicit
    • @pragma sriprecspc
  • @include and @include_once
  • Comments
  • Reserved Words
  • Values
    • Numbers
    • Map
    • Array
    • Multidimensional Map/Array
  • Operators
  • Control Strucutres
  • Function
  • Variable
    • Built-in Variable
  • Pipes
  • Garbage Collection
  • Modules
    • Hawk
    • String
    • System
    • ffi
    • mysql
  • Incompatibility with AWK
    • Parameter passing
  • Positional variable expression

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: 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.

Building Hawk From Source Code

Hawk uses autoconf and automake for building. Run the following commands to configure and compile Hawk:

$ ./configure ## This step offers various build options
$ make
$ make install

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 { print ARGV[0]"
	"   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"), /* ARGV[0] */
		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.

Assuming the above sample code is stored in hawk02.c and the built Hawk library has been installed properly, you may compile the sample code by running the following commands:

$ gcc -Wall -O2 -o hawk02 hawk02.c -lhawk

The actual command may vary depending on the compiler used and the library configure options used.

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 created by an individual whose name starts with H, hence the H in the name. It serves a dual purpose: to be an easy-to-embed implementation within other applications and a standalone tool for users. At its core, Hawk largely supports all the fundamental features of AWK, ensuring compatibility with existing AWK programs and scripts. However, it introduces subtle differences in behavior compared to traditional AWK implementations, which will be explained in the Incompatibility with AWK section.

In Hawk, as in traditional awk, the execution flow follows a specific order: the BEGIN block is executed first, followed by the pattern-action blocks, and finally the END block.

1. BEGIN Block: The BEGIN block is executed before any input is processed. It is typically used for initializations, such as setting variable values or defining functions that will be used later in the script.
2. Pattern-Action Blocks: After the BEGIN block, Hawk reads the input line by line (or record by record, depending on the record separator RS). For each input line or record, Hawk checks if it matches the specified pattern. If a match is found, the associated action block is executed.
3. END Block: After processing all input lines or records, the END block is executed. It is typically used for performing final operations, such as printing summaries or closing files.

Here's a sample code that demonstrates the basic BEGIN, pattern-action, and END loop in Hawk:

BEGIN {
	print "Starting the script..."
	total = 0
}
/^[0-9]+$/ { # Pattern-action block to sum up the numbers
	total += $0  # Add the current line (which is a number) to the total
}
END {
	print "The sum of all numbers is:", total
}

In this example:

1. The BEGIN block is executed first, printing the message "Starting the script..." and initializing the total variable to 0.
2. For each input line, Hawk checks if it matches the regular expression /^[0-9]+$/ (which matches lines containing only digits). If a match is found, the action block { total += $0 } is executed, adding the current line (treated as a number) to the total variable.
3. After processing all input lines, the END block is executed, printing the final message "The sum of all numbers is: total", where total is the accumulated sum of all numbers from the input.

You can provide input to this script in various ways, such as piping from another command, reading from a file, or entering input interactively. For example:

$ echo -e "42\n3.14\n100" | hawk -f sum.hawk
Starting the script...
The sum of all numbers is: 142

In this example, the sum.hawk file contains the Hawk script that sums up the numbers from the input. The input is provided via the echo command, which outputs three lines: 42, 3.14 (ignored because it doesn't match the pattern), and 100. The script sums up the numbers 42 and 100, resulting in a total of 142.

It's important to note that if there is no action-pattern block or END block present in the Hawk script, the interpreter will not wait for input records. In this case, the script will execute only the BEGIN block (if present) and then immediately terminate.

However, if an action-pattern block or an END block is present in the script, even if there is no action-pattern block, Hawk will wait for input records or lines. This behavior is consistent with the way awk was designed to operate: it expects input data to process unless the script explicitly indicates that no input is required.

For example, consider the following command:

$ ls -l | hawk 'END { print NR; }'

In this case, the Hawk script contains only an END block that prints the value of the NR(Number of Records) variable, which keeps track of the number of input records processed. Since there is an END block present, Hawk will wait for input records from the ls -l command, process them (though no action is taken for each record), and finally execute the END block, printing the total number of records processed.

Additionally, Hawk introduces the @pragma entry feature, which allows you to change the entry point of your script to a custom function instead of the default BEGIN block. This feature will be covered in the Pragmas section.

Pragmas

The @pragma keyword enables you to modify Hawk’s behavior. You can place a pragma item at the file scope within any source files. Additionally, a pragma item at the global scope can appear only once across all source files.

Name	Scope	Values	Default	Description
entry	global	function name		change the program entry point
implicit	file	on, off	on	allow undeclared variables
multilinestr	file	on, off	off	allow a multiline string literal without continuation
striprecspc	global	on, off	off	removes leading and trailing blank fields in splitting a record if FS is a regular expression mathcing all spaces
stripstrspc	global	on, off	on	trim leading and trailing spaces when converting a string to a number
numstrdetect	global	on, off	on	trim leading and trailing spaces when converting a string to a number
stack_limit	global	number	5120	specify the runtime stack size measured in the number of values

@pragma entry

In addition to the standard BEGIN and END blocks found in awk, Hawk introduces the @pragma entry feature, which allows you to specify a custom entry point function. This can be useful when you want to bypass the default BEGIN block behavior and instead start executing your script from a specific function.

The @pragma entry pragma is used to define the entry point function, like this:

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

In this example, the main function is set as the entry point for script execution. When the script is run, Hawk will execute the code inside the main function instead of the BEGIN block.

You can also pass arguments to the entry point function by defining it with parameters:

@pragma entry main
function main(arg1, arg2) {
	print "Arguments:", arg1, arg2
}

In this example, let's assume the script is saved as main.hawk. The main function is set as the entry point for script execution, and it accepts two arguments, arg1 and arg2. Then, when executing the main.hawk script, you can provide the arguments like this:

$ hawk -f main.hawk arg1_value arg2_value

This will cause Hawk to execute the code inside the main function, passing arg1_value and arg2_value as the respective values for arg1 and arg2.

This flexibility in specifying the entry point can be useful in various scenarios, such as:

• Modular Script Design: You can organize your script into multiple functions and specify the entry point function, making it easier to manage and maintain your code.
• Command-line Arguments: By defining the entry point function with parameters, you can easily accept and process command-line arguments passed to your script.
• Testing and Debugging: When working on specific parts of your script, you can temporarily set the entry point to a different function, making it easier to test and debug that particular functionality.
• Integration with Other Systems: If you need to embed Hawk scripts within a larger application or system, you can use the @pragma entry feature to specify the function that should be executed as the entry point, enabling better integration and control over the script execution flow.

If you don't know the number of arguments in advance, you can use the ellipsis ... in the parameter list and access the variadic arguments using @argv() and @argc().

@pragma entry main
function main(...) {
	@local i
	for (i = 0; i < @argc; i++) printf("%s:", @argv[i])
	print ""
}

In this example, the main function can accept variable number of arguments.

$ hawk -f main.hawk 10 20 30 40 50

The expected output of the above command is 10:20:30:40:50:.

It's important to note that if you don't define an entry point function using @pragma entry, Hawk will default to the standard awk behavior and execute the BEGIN block first, followed by the pattern-action blocks, and finally the END block.

Overall, the @pragma entry feature in Hawk provides you with greater flexibility and control over the execution flow of your scripts, allowing you to tailor the entry point to your specific needs and requirements.

@pragma implicit

Hawk also introduces the @pragma implicit feature, which allows you to enforce variable declarations. Unlike traditional awk, where local variable declarations are not necessary, Hawk can require you to declare variables before using them. This is controlled by the @pragma implicit pragma:

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

In the example above, the @pragma implicit off directive is used to turn off implicit variable declaration. As a result, attempting to use the undeclared variable a will result in a syntax error.

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

With the @local declaration, the variable a is explicitly declared, allowing it to be used without triggering a syntax error. This feature can be beneficial for catching potential variable misspellings or unintended uses of global variables, promoting better code quality and maintainability.

If you don't want to enforce variable declarations, you can simply omit the @pragma implicit off directive or specify @pragma implicit on, and Hawk will behave like traditional awk, allowing implicit variable declarations.

@pragma sriprecspc

The @pragma striprecspc directive in Hawk controls how the interpreter handles leading and trailing blank fields in input records when using a regular expression as the field separator (FS).

When you set FS to a regular expression that matches one or more whitespace characters (e.g., FS="[[:space:]]+"), Hawk will split the input records into fields based on that pattern. By default, Hawk follows the behavior of traditional awk, which means that leading and trailing blank fields are preserved.

However, Hawk introduces the @pragma striprecspc directive, which allows you to change this behavior. Here's how it works:

• @pragma striprecspc on

$ echo '  a  b  c  d  ' | hawk '@pragma striprecspc on;
BEGIN { FS="[[:space:]]+"; }
{
    print "NF=" NF;
    for (i = 0; i < NF; i++) print i " [" $(i+1) "]";
}'
NF=4
0 [a]
1 [b]
2 [c]
3 [d]

When @pragma striprecspc on is set, Hawk will automatically remove any leading and trailing blank fields from the input records. In the example above, the input string ' a b c d ' has a leading and trailing space, which would normally result in two additional blank fields. However, with @pragma striprecspc on, these blank fields are stripped, and the resulting NF(number of fields) is 4, corresponding to the fields "a", "b", "c", and "d".

• @pragma striprecspc off

$ echo '  a  b  c  d  ' | hawk '@pragma striprecspc off;
BEGIN { FS="[[:space:]]+"; }
{
    print "NF=" NF;
    for (i = 0; i < NF; i++) print i " [" $(i+1) "]";
}'
NF=6
0 []
1 [a]
2 [b]
3 [c]
4 [d]
5 []

When @pragma striprecspc off is set (or the directive is omitted, as this is the default behavior), Hawk preserves any leading and trailing blank fields in the input records. In the example above, the input string ' a b c d ' has a leading and trailing space, resulting in two additional blank fields. The NF(number of fields) is now 6, with the first and last fields being empty, and the remaining fields containing "a", "b", "c", and "d".

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

However, some of these words not beginning with @ 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 definition with the same name.

Values

• uninitialized value
• character
• integer
• floating-point number
• string
• byte string
• array - light-weight array with numeric index only
• map - conventional AWK array
• function
• regular expression
• reference to a value

To know the current type name 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");
}

hawk::type() returns a numeric type code:

• hawk::VAL_ARRAY
• hawk::VAL_BCHAR
• hawk::VAL_CHAR
• hawk::VAL_FLT
• hawk::VAL_INT
• hawk::VAL_MAP
• hawk::VAL_MBS
• hawk::VAL_NIL
• hawk::VAL_STR
• hawk::VAL_REF
• hawk::VAL_REX

A regular expression literal is special in that it never appears as an independent 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 expression 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 floating-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 floating point with a preceding number.

• 369 # integer
• 3.69 # floating-point 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-insensitively 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.

Map

BEGIN {
	@local x, i;
	x = hawk::map(); ## you can omit this line
	x["one"] = 1;
	x["two"] = 2;
	x[199] = 3;
	for (i in x) print i, x[i];
}

Array

BEGIN {
	@local x, i
	x = hawk::array()
	for (i = 0; i < 20; i++) x[i] = i;
	print hawk::isarray(x), hawk::ismap(x)
	print "--------------";
	for (i in x) print i, x[i];
}

Multidimensional Map/Array

BEGIN {
        @local x, i, j, k;
        k = hawk::array();

        x = hawk::array();
        k[0] = x;
        k[1] = x;

        for (i = 0; i < 20; i++) x[i] = i;
        k[0][0] = 99;
        for (j in k)
                for (i in x) print j, i, x[i];
}

Operators

• ===, ==, !==, !=
• +, -, *, %
• &&, ||, &, |

Control Structures

Hawk supports various control structures for flow control and iteration, similar to those found in awk.

The if statement in Hawk follows the same syntax as in awk and other programming languages. It allows you to execute a block of code conditionally based on a specified condition.

if (condition) {
	## statements
} else if (another_condition) {
	## other statements
} else {
	## default statements
}

The while loop in Hawk is used to repeatedly execute a block of code as long as a specific condition is true.

while (condition) {
	# statements
}

The do-while loop is similar to the while loop, but it guarantees that the code block will be executed at least once, as the condition is evaluated after the first iteration.

do {
	# statements
} while (condition)

The for loop in Hawk follows the same syntax as in awk and allows you to iterate over a range of values or an array.

for (initialization; condition; increment/decrement) {
	## statements
}

You can also use the for loop to iterate over the elements of an array:

for (index in array) {
	## statements using array[index]
}

Hawk also supports the break and continue statements, which work the same way as in awk and other programming languages. The break statement is used to exit a loop prematurely, while continue skips the remaining statements in the current iteration and moves to the next iteration.

TODO: return exit nextfile nextofile

Here are some examples demonstrating the usage of control structures in Hawk.

• Check if a number is even or odd

{
	if ($1 % 2 == 0) {
		print $1, "is an even number"
	} else {
		print $1, "is an odd number"
	}
}

• Print the first 10 even numbers

BEGIN {
	i = 0
	n = 1
	while (i < 10) {
		if (n % 2 == 0) {
			print n
			i++
		}
		n++
	}
}

• Prompt the user for a positive number

BEGIN {
	do {
		printf "Enter a positive number: "
		getline num
	} while (num <= 0)
	print "You entered:", num
}

• Print the multiplication table

BEGIN {
	for (i = 1; i <= 10; i++) {
		for (j = 1; j <= 10; j++) {
			printf "%4d", i * j
		}
		printf "\n"
	}
}

• Print only the even numbers from 1 to 16

BEGIN {
	for (i = 1; i <= 20; i++) {
		if (i % 2 != 0) {
			continue
		}
		print i
		if (i >= 16) {
			break
		}
	}
}

• Count the frequency of words in a file

{
	n = split($0, words, /[^[:alnum:]_]+/)
	for (i = 1; i <= n; i++) {
		freq[words[i]]++
	}
}

END {
	for (w in freq) {
		printf "%s: %d\n", w, freq[w]
	}
}

The syntax and behavior of these structures are largely consistent with awk, making it easy for awk users to transition to Hawk and leverage their existing knowledge.

Function

Hawk supports user-defined functions, enabling developers to break down complex logic into modular component for reuse. Hawk also provides a wide range of built-in functions that extend its capabilities for various tasks, such as string manipulation, array handling, and more.

To define a function in Hawk, you use the function keyword followed by the function name and a set of parentheses to enclose the optional function parameters:

function function_name(parameter1, parameter2, ...) {
	## function body
	## statements
	return value
}

Functions in Hawk can accept parameters, perform operations, and optionally return a value using the return statement.

Here's an example of a function that calculates the factorial of 10:

function factorial(n) {
	if (n <= 1) {
		return 1
	} else {
		return n * factorial(n - 1)
	}
}

BEGIN {
	num = 10
	result = factorial(num)
	print "The factorial of", num, "is", result
}

If no return statement is encountered, the function returns @nil, which is Hawk's equivalent of nil or null in other programming languages.

function a() { k=999; }
BEGIN { k=a(); print k === @nil, k === "", k == ""; }

The expected output of the above example code is 1 0 1.

• k === @nil: This expression evaluates to 1 (true) because k is indeed equal to @nil when using the type-precise === operator.
• k === "": This expression evaluates to 0 (false) because k is not equal to an empty string when using the type-precise === operator.
• k == "": This expression evaluates to 1 (true) because @nil is considered equal to an empty string when using the double equal sign == operator.

Functions can be called from various contexts, including BEGIN, pattern-action blocks, and END blocks, as well as from other functions. They can be defined before or after they are used, as Hawk resolves function references.

You can pass fewer arguments than the number of declared parameters to a function. In such cases, the missing parameters are treated as having @nil.

Here's an example to illustrate this behavior:

@function greet(name, greeting) {
    if (greeting == "") {
        greeting = "Hello"
    }
    print greeting, name
}

BEGIN {
    greet("Alice", "Hi")     ## Output: Hi Alice
    greet("Bob")             ## Output: Hello Bob
    greet()                  ## Output: Hello
}

In the above example:

1. The greet function is defined with two parameters: name and greeting.
2. In the first function call greet("Alice", "Hi"), both arguments are provided, so name is assigned "Alice", and greeting is assigned "Hi".
3. In the second function call greet("Bob"), only one argument is provided. Therefore, name is assigned "Bob", and greeting is assigned @nil. The function checks if greeting is empty and assigns the default value "Hello".
4. In the third function call greet(), no arguments are provided. Both name and greeting are assigned @nil. The function then assigns the default value "Hello" to greeting and prints "Hello".

However, it's important to note that you cannot pass more arguments than the number of declared parameters in a function. If you attempt to do so, Hawk will raise an error.

Variable

Variables can be used to store and manipulate data. There are two types of variables:

• Built-in Variables: These are predefined variables provided by the awk language itself. They are used for specific purposes and contain information about the input data or the state of the program.
• User-defined Variables: These are variables created and used by the programmer to store and manipulate data as needed within the program.

You can declare variables explicitly using the following syntax:

1. Local Variables:
   • Declared using @local var_1, var_2, ...
   • These variables are scoped within the current block or function.
2. Global Variables:
   • Declared using @global var_1, var_2, ...
   • These variables are accessible throughout the entire Hawk program.

While explicit variable declaration is supported, Hawk also maintains compatibility with awk by allowing implicit variable creation and usage. See @pragma implicit on how to control this behavior.

@global count, total;  # Global variables

BEGIN {
	@local i, j;  ## Local variables in the BEGIN block
	count = 0;
	total = 0;
}

{
	@local value;  ## Local variable in the main block
	value = $1 + $2;
	count++;
	total += value;
}

END {
	print "Total count:", count;
	print "Sum of values:", total;
}

In this example:

• count and total are global variables declared using @global.
• i and j are local variables declared in the BEGIN block using @local.
• value is a local variable declared in the main block using @local.

Built-in Variable

Variable	Description
CONVFMT
FILENAME
FNR	File Number of Records, reset to 1 for each new input file
FS	Field Separator, specifies the character(s) that separate fields (columns) in an input record. Default is whitespace
IGNORECASE
NF	Number of Fields (columns) in the current input record
NR	Number of Records processed so far
NUMSTRDETECT
OFILENAME
OFMT
OFS
ORS
RLENGTH
RS	Record Separator, specifies the character(s) that separate input records (lines). Default is newline "\n"
RSTART
SCRIPTNAME
STRIPRECSPC
STRIPSTRSPC
SUBSPEP

Pipes

BEGIN {
	while (("ls -laF" | getline x) > 0) print "\t", x;
	close ("ls -laF");
}

{ print $0 | "cat" }
END { close("cat"); print "ENDED"; }

Garbage Collection

The primary value management is reference counting based but map and array values are garbage-collected additionally.

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::type
• 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 third 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 respectively. 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