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#!/bin/bash

process_file_lines() {
    local input_file="$1"
    local output=""

    # Read the input file and process it line by line
    previous_line=""
    while read -r line; do
        if [[ ! $line =~ ^\[2 ]]; then
            previous_line+="$line"
        else
            if [[ -n $previous_line ]]; then
                output+="$previous_line"$'\n'
            fi
            previous_line=$line
        fi
    done < "$input_file"

    # Append the last line
    if [[ -n $previous_line ]]; then
        output+="$previous_line"$'\n'
    fi

    # Return the output as a printf %q quoted string
    printf %q "$output"
}

# Usage example
input_file="input.txt" # Replace this with the actual input file path
processed_output="$(process_file_lines "$input_file")"
# Use printf %b to properly unquote the output variable
printf "\nProcessed output:\n%b\n" "$processed_output"