catn

#!/bin/bash

usage() {
	local bin=${0##*/}
	[[ $1 -eq 0 ]] || exec 1>&2
	echo "Usage: $bin [-q] file line ctx_lines"
	echo "  or: $bin [-q] file line[:ctx_lines]"
	echo "  or: $bin [-q] file:line[:ctx_lines]"
	# [[ $1 -ne 0 ]] || { echo; echo "more help stuff"; }
	exit ${1:-1}; }
[[ "$1" != -h && "$1" != --help ]] || usage 0

q=
[[ "$1" = -q ]] && { q=t; shift; }
[[ -n "$1" ]] || usage 1
# set -eo pipefail

ctx=
case "$#" in
	3) file=$1 line=$2 ctx=$3 ;;
	2) file=$1 line=$2 ;;
	1)
		[[ $1 =~ : ]] || usage 1
		file=${1%:*} line=${1#*:} ;;
	0) usage ;;
	*) usage 1
esac

[[ -z "$file" || -z "$line" ]] && usage 1

[[ -z "$ctx" ]] && {
	[[ $line =~ : ]] && ctx=${line#*:} || ctx=3
}
line=${line%:*}

line_min=$(( $line - $ctx ))
line_max=$(( $line + $ctx ))

[[ -z "$q" ]]\
	&& line_fmt='{pre=NR=='"$line"' ? ">>" : "  "; printf("%s %d: %s\n", pre, NR, $0)}'\
	|| line_fmt=''

exec awk "NR>=${line_min} && NR<=${line_max} ${line_fmt}" "$file"