Print random range of lines from a file

rr_line.sh

#!/bin/bash

if [[ -z "$1" ]]; then
	# Read shell parameter expansion to understand better what this answer do
	# https://stackoverflow.com/a/965072/3832827
	# https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html
	echo "usage: $(basename $0) <file_name> [show_n_lines]";
	exit 1;
fi

file_name=$1
show_n_lines=$2

if [[ -z "${show_n_lines}" ]]; then
	show_n_lines=$(( $(tput lines) - 4 ))
fi

n_lines=$(wc -l ${file_name} | cut -f 1 -d ' ')
bottom_limit=$(( ${n_lines} + 1 ))
upper_limit=$(( ${bottom_limit} - ${show_n_lines} ))
width=$(( $(tput cols) - 1 ))

random_first_line=$(( $RANDOM % ${upper_limit} ))
random_last_line=$(( ${random_first_line} + ${show_n_lines} ))

cat -n ${file_name} | sed -n "${random_first_line},${random_last_line}p" | cut -c1-${width}