#!/bin/bash
# fixlines.sh
# Append \\'s

# Check if a filename was provided
if [ -z "$1" ]; then
    echo "Usage: $0 filename"
    exit 1
fi

# Edit the file in-place
sed -i -E '$!N; s/^([^\n]+)\n([^\n]+)/\1\\\\\n\2/; P; D' "$1"