Task 056: .BAS File Format

1. Properties of the .BAS File Format Intrinsic to Its File System

The .BAS file format primarily refers to BASIC Source Code files, which store programs written in the BASIC (Beginner's All-purpose Symbolic Instruction Code) programming language. This format has evolved across various dialects and implementations (e.g., Visual Basic, GW-BASIC, QuickBASIC, FreeBASIC, ZX Spectrum BASIC). While most .BAS files are plain-text files containing human-readable source code, some older or specific variants (e.g., GW-BASIC or QuickBASIC) may use tokenized binary formats for storage, which are not directly human-readable without a compatible interpreter. The format is not a structured binary file system like ZIP or PDF but rather a simple text-based or tokenized representation of code, with intrinsic properties tied to its role as a source code container.

Based on established specifications and analyses from reliable sources, the key intrinsic properties are enumerated below. These focus on structural, syntactic, and systemic attributes inherent to the format, independent of external tools or dialects unless noted as variant-specific:

• File Extension: .bas (standard identifier for BASIC source code files across platforms).
• Content Type: Plain text (ASCII or UTF-8 encoded source code for most implementations); tokenized binary in variants like GW-BASIC, QuickBASIC 4.5, or ZX Spectrum BASIC (e.g., starts with binary line number tokens).
• MIME Type: text/plain (for text-based .BAS files; binary variants may lack a formal MIME but are treated as application/octet-stream).
• Character Encoding: ASCII (default for legacy systems); UTF-8 (modern cross-platform support, without BOM for reliability); some dialects support Unicode for non-Latin characters.
• File Structure:
• Text-based: Line-oriented, with optional line numbers (e.g., 10 PRINT "Hello"); multi-statement lines separated by :; comments prefixed by ' or REM; optional headers like Attribute VB_Name = "Module1" in Visual Basic modules.
• Tokenized binary: Binary-encoded lines starting with 2-byte little-endian line number (e.g., 0x0A00 for line 10), followed by tokenized keywords (single-byte tokens for efficiency) and ASCII data; ends with EOF marker (e.g., 0xFF).
• Header/Signature: No universal binary header; text files may begin with Attribute VB_Name (Visual Basic) or line numbers; binary files often start with 0x00 or low-value bytes indicating tokenization.
• Data Elements: Source code statements (e.g., PRINT, INPUT, GOTO); variables (e.g., numeric or string); subroutines (SUB/END SUB in some dialects); no formal metadata section unless dialect-specific (e.g., optional AUTO line in ZX Spectrum .BAS for starting line number).
• Line Delimitation: Standard newline characters (\n on Unix/Linux/macOS, \r\n on Windows); multi-statement lines use : separator or backslash (\) in some editors for continuation.
• Keyword Handling: Plain text keywords (e.g., "PRINT") in text files; single-byte tokens (e.g., 0xAF for PRINT in GW-BASIC) in binary variants.
• Comments and Formatting: Comments start with ' or REM; supports control characters for colors/graphics in Spectrum BASIC; no indentation enforcement (free-form within lines).
• Size and Scalability: Typically small (170 bytes to 47 KB); no inherent size limit, but legacy systems capped at 64 KB or less.
• Endianness (Binary Variants Only): Little-endian for line numbers and integers.
• EOF Marker (Binary Variants Only): Specific byte sequences (e.g., 0xFF or repeated 0x00) to denote end of program.
• Cross-Platform Compatibility: High for text-based files (editable in any text editor); low for binary/tokenized files, requiring emulators or specific loaders (e.g., QB64 for QuickBASIC).
• Versioning/Support: Dialect-dependent (e.g., Visual Basic 6, FreeBASIC); no built-in version field, inferred from syntax or tokens.
• Associated Risks: Binary variants may appear "scrambled" if opened as text; potential for malware if executed in interpreters.

These properties are derived from analyses of common implementations, as there is no single universal specification for .BAS due to its historical and dialectal diversity.

2. Python Class for Handling .BAS Files

The following Python class, BASFileHandler, opens a .BAS file, detects if it is text-based or tokenized (basic heuristic for GW-BASIC/QuickBASIC-style binary), reads/decodes the properties listed above where applicable, writes modified content back to a file, and prints the properties to the console. For simplicity, it assumes text-based files as primary (common case); binary decoding is partial (line count and first line number) as full tokenization requires dialect-specific logic. It uses built-in libraries only.

import os
import sys

class BASFileHandler:
    def __init__(self, filepath):
        self.filepath = filepath
        self.content_type = None  # 'text' or 'binary'
        self.encoding = None
        self.file_structure = None
        self.header_signature = None
        self.line_delimitation = None
        self.properties = {}

    def open_and_decode(self):
        if not os.path.exists(self.filepath):
            raise FileNotFoundError(f"File {self.filepath} not found.")
        
        # Read as binary first to detect type
        with open(self.filepath, 'rb') as f:
            raw_data = f.read()
        
        # Heuristic: If starts with printable ASCII and no low bytes, assume text
        if all(32 <= b <= 126 or b in (10, 13) for b in raw_data[:100]) and raw_data[:100].decode('ascii', errors='ignore').strip():
            self.content_type = 'text'
            try:
                with open(self.filepath, 'r', encoding='utf-8') as f:
                    text_data = f.read()
                self.encoding = 'utf-8'
                self.header_signature = text_data[:50].strip()[:20] + '...' if len(text_data) > 20 else text_data.strip()
                self.file_structure = 'Line-oriented text with optional line numbers'
                self.line_delimitation = 'LF' if b'\n' in raw_data and b'\r\n' not in raw_data else 'CRLF'
                lines = text_data.splitlines()
                self.properties = {
                    'File Extension': '.bas',
                    'Content Type': self.content_type,
                    'MIME Type': 'text/plain',
                    'Character Encoding': self.encoding,
                    'File Structure': self.file_structure,
                    'Header/Signature': self.header_signature,
                    'Line Delimitation': self.line_delimitation,
                    'Data Elements': f'Approximately {len(lines)} lines of BASIC code',
                    'Keyword Handling': 'Plain text keywords',
                    'Size': f'{len(raw_data)} bytes'
                }
                return text_data
            except UnicodeDecodeError:
                with open(self.filepath, 'r', encoding='ascii') as f:
                    text_data = f.read()
                self.encoding = 'ascii'
                # Update properties similarly...
                self.properties['Character Encoding'] = self.encoding
                return text_data
        else:
            self.content_type = 'binary'
            self.encoding = 'N/A (tokenized)'
            self.header_signature = f'Binary: {raw_data[:4].hex()}'
            # Basic binary decode: Count lines (pairs of 2-byte 0x00-terminated)
            line_count = sum(1 for i in range(0, len(raw_data), 1) if raw_data[i:i+2] == b'\x00\x00')  # Simplified heuristic
            first_line_num = int.from_bytes(raw_data[2:4], 'little') if len(raw_data) > 4 else 0  # Assume offset
            self.file_structure = f'Tokenized binary with {line_count} lines'
            self.line_delimitation = 'N/A'
            self.properties = {
                'File Extension': '.bas',
                'Content Type': self.content_type,
                'MIME Type': 'application/octet-stream',
                'Character Encoding': self.encoding,
                'File Structure': self.file_structure,
                'Header/Signature': self.header_signature,
                'Line Delimitation': self.line_delimitation,
                'Data Elements': f'First line number: {first_line_num}',
                'Keyword Handling': 'Single-byte tokens',
                'Size': f'{len(raw_data)} bytes'
            }
            return raw_data  # Return raw for writing

    def write(self, output_path, data):
        mode = 'w' if self.content_type == 'text' else 'wb'
        with open(output_path, mode) as f:
            if self.content_type == 'text':
                f.write(data)
            else:
                f.write(data)
        print(f"Written to {output_path}")

    def print_properties(self):
        for key, value in self.properties.items():
            print(f"{key}: {value}")

# Example usage (commented out for class definition)
# handler = BASFileHandler('example.bas')
# data = handler.open_and_decode()
# handler.print_properties()
# handler.write('output.bas', data)  # For write, pass modified data if needed

To use: Instantiate the class with a file path, call open_and_decode() to read/decode, print_properties() to display, and write() to save (optionally modified) content.

3. Java Class for Handling .BAS Files

The following Java class, BASFileHandler, performs analogous operations using standard Java I/O. It detects text vs. binary, extracts properties, and supports read/write. Compile with javac BASFileHandler.java and run with java BASFileHandler <filepath>.

import java.io.*;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;

public class BASFileHandler {
    private String filepath;
    private String contentType;
    private String encoding;
    private Map<String, String> properties;

    public BASFileHandler(String filepath) {
        this.filepath = filepath;
        this.properties = new HashMap<>();
    }

    public byte[] openAndDecode() throws IOException {
        if (!new java.io.File(filepath).exists()) {
            throw new FileNotFoundException("File not found: " + filepath);
        }

        byte[] rawData = Files.readAllBytes(Paths.get(filepath));

        // Heuristic for text: Check first 100 bytes for printable ASCII
        boolean isText = true;
        for (int i = 0; i < Math.min(100, rawData.length); i++) {
            byte b = rawData[i];
            if (!(b >= 32 && b <= 126 || b == 10 || b == 13)) {
                isText = false;
                break;
            }
        }

        if (isText) {
            contentType = "text";
            try {
                String textData = new String(rawData, StandardCharsets.UTF_8);
                encoding = "UTF-8";
                String header = textData.substring(0, Math.min(50, textData.length())).trim().substring(0, 20) + "..." 
                                + (textData.length() > 20 ? "..." : "");
                String structure = "Line-oriented text with optional line numbers";
                String delim = new String(rawData).contains("\r\n") ? "CRLF" : "LF";
                int lineCount = textData.split("\n").length;
                properties.put("File Extension", ".bas");
                properties.put("Content Type", contentType);
                properties.put("MIME Type", "text/plain");
                properties.put("Character Encoding", encoding);
                properties.put("File Structure", structure);
                properties.put("Header/Signature", header);
                properties.put("Line Delimitation", delim);
                properties.put("Data Elements", "Approximately " + lineCount + " lines of BASIC code");
                properties.put("Keyword Handling", "Plain text keywords");
                properties.put("Size", rawData.length + " bytes");
                return textData.getBytes(StandardCharsets.UTF_8);
            } catch (Exception e) {
                String textData = new String(rawData, StandardCharsets.US_ASCII);
                encoding = "ASCII";
                properties.put("Character Encoding", encoding);
                // Similar updates...
                return textData.getBytes(StandardCharsets.US_ASCII);
            }
        } else {
            contentType = "binary";
            encoding = "N/A (tokenized)";
            String header = "Binary: " + bytesToHex(rawData, 0, 4);
            // Basic binary: First line num (bytes 2-3, little-endian)
            int firstLine = (rawData.length > 3) ? ((rawData[3] & 0xFF) << 8 | (rawData[2] & 0xFF)) : 0;
            int lineCount = 0; // Simplified: count 0x00 pairs
            for (int i = 0; i < rawData.length - 1; i += 2) {
                if (rawData[i] == 0 && rawData[i+1] == 0) lineCount++;
            }
            String structure = "Tokenized binary with " + lineCount + " lines";
            properties.put("File Extension", ".bas");
            properties.put("Content Type", contentType);
            properties.put("MIME Type", "application/octet-stream");
            properties.put("Character Encoding", encoding);
            properties.put("File Structure", structure);
            properties.put("Header/Signature", header);
            properties.put("Line Delimitation", "N/A");
            properties.put("Data Elements", "First line number: " + firstLine);
            properties.put("Keyword Handling", "Single-byte tokens");
            properties.put("Size", rawData.length + " bytes");
            return rawData;
        }
    }

    private String bytesToHex(byte[] bytes, int start, int len) {
        StringBuilder sb = new StringBuilder();
        for (int i = start; i < start + len && i < bytes.length; i++) {
            sb.append(String.format("%02x", bytes[i]));
        }
        return sb.toString();
    }

    public void write(String outputPath, byte[] data) throws IOException {
        Files.write(Paths.get(outputPath), data);
        System.out.println("Written to " + outputPath);
    }

    public void printProperties() {
        for (Map.Entry<String, String> entry : properties.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }

    public static void main(String[] args) throws IOException {
        if (args.length != 1) {
            System.err.println("Usage: java BASFileHandler <filepath>");
            return;
        }
        BASFileHandler handler = new BASFileHandler(args[0]);
        byte[] data = handler.openAndDecode();
        handler.printProperties();
        // handler.write("output.bas", data); // Uncomment to write
    }
}

4. JavaScript Class for Handling .BAS Files

The following JavaScript class, BASFileHandler, uses Node.js File System module (require fs). Run with node BASFileHandler.js <filepath>. It handles Node.js environments for file I/O.

const fs = require('fs');
const path = require('path');

class BASFileHandler {
    constructor(filepath) {
        this.filepath = filepath;
        this.contentType = null;
        this.encoding = null;
        this.properties = {};
    }

    async openAndDecode() {
        if (!fs.existsSync(this.filepath)) {
            throw new Error(`File ${this.filepath} not found.`);
        }

        const rawData = await fs.promises.readFile(this.filepath);

        // Heuristic for text
        const isText = rawData.slice(0, 100).every(b => (b >= 32 && b <= 126) || b === 10 || b === 13);

        if (isText) {
            this.contentType = 'text';
            try {
                const textData = rawData.toString('utf8');
                this.encoding = 'utf-8';
                const header = textData.substring(0, Math.min(50, textData.length)).trim().substring(0, 20) + (textData.length > 20 ? '...' : '');
                const structure = 'Line-oriented text with optional line numbers';
                const delim = rawData.includes(Buffer.from('\r\n')) ? 'CRLF' : 'LF';
                const lines = textData.split('\n').length;
                this.properties = {
                    'File Extension': '.bas',
                    'Content Type': this.contentType,
                    'MIME Type': 'text/plain',
                    'Character Encoding': this.encoding,
                    'File Structure': structure,
                    'Header/Signature': header,
                    'Line Delimitation': delim,
                    'Data Elements': `Approximately ${lines} lines of BASIC code`,
                    'Keyword Handling': 'Plain text keywords',
                    'Size': rawData.length + ' bytes'
                };
                return textData;
            } catch (e) {
                const textData = rawData.toString('ascii');
                this.encoding = 'ascii';
                this.properties['Character Encoding'] = this.encoding;
                // Similar...
                return textData;
            }
        } else {
            this.contentType = 'binary';
            this.encoding = 'N/A (tokenized)';
            const header = 'Binary: ' + rawData.slice(0, 4).toString('hex');
            // Basic binary
            let firstLine = 0;
            if (rawData.length > 3) {
                firstLine = (rawData[3] << 8) | rawData[2];
            }
            let lineCount = 0;
            for (let i = 0; i < rawData.length - 1; i += 2) {
                if (rawData[i] === 0 && rawData[i+1] === 0) lineCount++;
            }
            const structure = `Tokenized binary with ${lineCount} lines`;
            this.properties = {
                'File Extension': '.bas',
                'Content Type': this.contentType,
                'MIME Type': 'application/octet-stream',
                'Character Encoding': this.encoding,
                'File Structure': structure,
                'Header/Signature': header,
                'Line Delimitation': 'N/A',
                'Data Elements': `First line number: ${firstLine}`,
                'Keyword Handling': 'Single-byte tokens',
                'Size': rawData.length + ' bytes'
            };
            return rawData;
        }
    }

    async write(outputPath, data) {
        await fs.promises.writeFile(outputPath, data);
        console.log(`Written to ${outputPath}`);
    }

    printProperties() {
        for (const [key, value] of Object.entries(this.properties)) {
            console.log(`${key}: ${value}`);
        }
    }
}

// Example usage
if (require.main === module) {
    const args = process.argv.slice(2);
    if (args.length !== 1) {
        console.error('Usage: node BASFileHandler.js <filepath>');
        process.exit(1);
    }
    (async () => {
        const handler = new BASFileHandler(args[0]);
        const data = await handler.openAndDecode();
        handler.printProperties();
        // await handler.write('output.bas', data);
    })();
}

module.exports = BASFileHandler;

5. C Class (Struct with Functions) for Handling .BAS Files

The following C implementation uses standard library functions (stdio.h, stdlib.h). It is a procedural "class" via struct and functions. Compile with gcc -o bas_handler bas_handler.c and run ./bas_handler <filepath>.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    char* filepath;
    char* content_type;
    char* encoding;
    // Properties as key-value, but for simplicity, print directly
} BASHandler;

BASHandler* bas_handler_create(const char* filepath) {
    BASHandler* h = malloc(sizeof(BASHandler));
    h->filepath = strdup(filepath);
    h->content_type = NULL;
    h->encoding = NULL;
    return h;
}

void bas_handler_destroy(BASHandler* h) {
    free(h->filepath);
    free(h->content_type);
    free(h->encoding);
    free(h);
}

char* bytes_to_hex(const unsigned char* bytes, int len) {
    char* hex = malloc(2 * len + 1);
    for (int i = 0; i < len; i++) {
        sprintf(hex + 2*i, "%02x", bytes[i]);
    }
    hex[2*len] = '\0';
    return hex;
}

unsigned char* bas_open_and_decode(BASHandler* h) {
    FILE* f = fopen(h->filepath, "rb");
    if (!f) {
        perror("File not found");
        return NULL;
    }

    fseek(f, 0, SEEK_END);
    long size = ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char* raw_data = malloc(size);
    fread(raw_data, 1, size, f);
    fclose(f);

    // Heuristic for text
    int is_text = 1;
    for (int i = 0; i < (size < 100 ? size : 100); i++) {
        unsigned char b = raw_data[i];
        if (!((b >= 32 && b <= 126) || b == 10 || b == 13)) {
            is_text = 0;
            break;
        }
    }

    if (is_text) {
        h->content_type = strdup("text");
        h->encoding = strdup("UTF-8");  // Assume; check could be added
        char header[51];
        strncpy(header, (char*)raw_data, 50);
        header[50] = '\0';
        // Simplified; assume ASCII for print
        printf("File Extension: .bas\n");
        printf("Content Type: %s\n", h->content_type);
        printf("MIME Type: text/plain\n");
        printf("Character Encoding: %s\n", h->encoding);
        printf("File Structure: Line-oriented text with optional line numbers\n");
        printf("Header/Signature: %s...\n", header);
        // Line delim: simplified
        printf("Line Delimitation: LF\n");
        printf("Data Elements: BASIC code lines\n");
        printf("Keyword Handling: Plain text keywords\n");
        printf("Size: %ld bytes\n", size);
        return raw_data;  // As text bytes
    } else {
        h->content_type = strdup("binary");
        h->encoding = strdup("N/A (tokenized)");
        char* hex_header = bytes_to_hex(raw_data, 4);
        int first_line = (raw_data[3] << 8) | raw_data[2];  // Little-endian
        int line_count = 0;
        for (int i = 0; i < size - 1; i += 2) {
            if (raw_data[i] == 0 && raw_data[i+1] == 0) line_count++;
        }
        printf("File Extension: .bas\n");
        printf("Content Type: %s\n", h->content_type);
        printf("MIME Type: application/octet-stream\n");
        printf("Character Encoding: %s\n", h->encoding);
        printf("File Structure: Tokenized binary with %d lines\n", line_count);
        printf("Header/Signature: Binary: %s\n", hex_header);
        printf("Line Delimitation: N/A\n");
        printf("Data Elements: First line number: %d\n", first_line);
        printf("Keyword Handling: Single-byte tokens\n");
        printf("Size: %ld bytes\n", size);
        free(hex_header);
        return raw_data;
    }
}

void bas_write(BASHandler* h, const char* output_path, unsigned char* data, long size) {
    FILE* f = fopen(output_path, "wb");
    if (f) {
        fwrite(data, 1, size, f);
        fclose(f);
        printf("Written to %s\n", output_path);
    } else {
        perror("Write failed");
    }
}

int main(int argc, char* argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <filepath>\n", argv[0]);
        return 1;
    }
    BASHandler* h = bas_handler_create(argv[1]);
    unsigned char* data = bas_open_and_decode(h);
    if (data) {
        // bas_write(h, "output.bas", data, /*size*/ 0);  // Uncomment with size
        free(data);
    }
    bas_handler_destroy(h);
    return 0;
}

This C version prints properties directly in open_and_decode for simplicity, as dynamic key-value storage would require additional structures. For full write, pass size from file read.