- [Embedding Hawk in C Applications](#embedding-in-c-app)
- [Embedding Hawk in C++ Applications](#embedding-in-cxx-app)
- [Language](#language)
- [Modules](#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.
- 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 <div id="embedding-in-c-app"/>
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 */
/* 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 <div id="embedding-in-cxx-app"/>
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());
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.
`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](#incompatibility-with-awk) 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.
1. 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.
1. 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).
1. 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.
1. 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.
The `@prama` keyword allows you to change the Hawk's behaviors. 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.
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:
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:
In this example, let's assume the script is saved as `script.awk`. The `main` function is set as the entry point for script execution, and it accepts two arguments, `arg1` and `arg2`. Then, when executing the `script.awk` script, you can provide the arguments like this:
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`.
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:
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.
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.
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.
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.
- 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::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.
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
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.
