If you're working with large log files and you're not comfortable using vi or vim then you might want to split your log/text file into multiple parts based on the number of lines per file. You can run the following command to split the inputFile into a number of outputFiles each containing 5000 lines:
split -d -l 5000 inputFile outputFile
The -d option instructs the split command to use numeric suffixes for each outputFile.