Here's a Bash script that recursively traverses a directory, reads each file, and concatenates them into a single output file. It adds a comment at the top of each file's content using the appropriate syntax based on the file extension.

concatenate-files.sh

#!/bin/bash

# Function to get directory name from path
get_dirname() {
    local input_path="$1"
    local resolved_path

    # Check if realpath exists
    if command -v realpath >/dev/null 2>&1; then
        # Try to resolve the path fully
        resolved_path=$(realpath "$input_path" 2>/dev/null)
    elif command -v readlink >/dev/null 2>&1; then
        resolved_path=$(readlink -f "$input_path" 2>/dev/null)
    else
        # Fallback: use the input path as is
        resolved_path="$input_path"
    fi

    # If resolution failed (empty), fallback to input path
    if [ -z "$resolved_path" ]; then
        resolved_path="$input_path"
    fi

    # Check if the resolved path is a directory
    if [ -d "$resolved_path" ]; then
        # Return the directory name itself
        echo "$resolved_path"
    else
        # Get dirname of the resolved path
        dirname "$resolved_path"
    fi
}

# Function to determine comment syntax based on file extension
get_comment_prefix() {
    case "$1" in
        *.py|*.sh|*.pl|*.rb|*.r|*.yaml|*.yml|*.toml|*.ini|*.conf|*.cfg) echo "#" ;;
        *.c|*.cpp|*.h|*.java|*.js|*.ts|*.css|*.go|*.swift|*.kt|*.scala|*.cs|*.fs) echo "//" ;;
        *.vb) echo "'" ;;  # Visual Basic uses single quote for comments
        *.html|*.xml|*.cshtml|*.razor) echo "<!--" ;;
        *.php) echo "//" ;;
        *.sql) echo "--" ;;
        *) echo "#" ;;  # Default to hash
    esac
}

# Check if input directory is provided and exists
if [ -z "$1" ] || [ ! -d "$1" ]; then
    echo "Error: Please provide a valid directory path."
    exit 1
fi

# Get output filename from input directory path
output_filename=$(get_dirname "$1")

# Output file
output_file="$output_filename.txt"
> "$output_file"  # Clear the output file if it exists

# Traverse all files in the directory and subdirectories
find "$1" -type f | while IFS= read -r file; do
    ext="${file##*.}"
    comment_prefix=$(get_comment_prefix "$file")

    if [[ "$comment_prefix" == "<!--" ]]; then
        echo "${comment_prefix} @file $file -->" >> "$output_file"
    else
        echo "${comment_prefix} @file $file" >> "$output_file"
    fi

    cat "$file" >> "$output_file"
    echo -e "\n" >> "$output_file"
done

echo "Concatenation complete. Output saved to $output_file"