little-things/uniqify-recent

#!/bin/bash
if [[ $# -ge 1 && ( $# -gt 1 || ! "$1" =~ ^([0-9]|[1-9][0-9]*)(\.[0-9][0-9]*)?$ ) ]]; then
	printf 'Usage: uniqify-recent [N]\n' >&2
	printf 'After a line is read from stdin, its duplicates are suppressed for N seconds (default: 60)\n' >&2
	printf 'N may have a fractional part, e.g. 123456.789\n' >&2
	exit 1
fi

# EPOCHREALTIME was added in 4.4
if (( BASH_VERSINFO[0] < 4 || ( BASH_VERSINFO[0] == 4 && BASH_VERSINFO[1] < 4 ) )); then
	printf 'Error: this requires Bash 4.4 or higher\n' >&2
	exit 1
fi

limit=60000000
if [[ $# -eq 1 ]]; then
	if [[ "$1" == *.* ]]; then
		seconds="${1%.*}"
		fraction="${1#*.}"
	else
		seconds="$1"
		fraction=
	fi
	fraction="${fraction}000000"
	fraction="${fraction:0:6}"
	limit=$((seconds * 1000000 + fraction))
fi

# Bash 5.2 added ridiculousness in arithmetic context expansion of associative arrays. Revert that nonsense.
if (( BASH_VERSINFO[0] > 5 || ( BASH_VERSINFO[0] == 5 && BASH_VERSINFO[1] >= 2 ) )); then
	BASH_COMPAT=51
fi

declare -A lastseen
lastclean=${EPOCHREALTIME/./}

while IFS= read -r l; do
	now=${EPOCHREALTIME/./}
	if [[ ! -v 'lastseen[$l]' ]] || (( now - lastseen[\$l] > limit )); then
		printf '%s\n' "$l"
		lastseen["${l}"]="${now}"
	fi
	if (( now - lastclean > 10 * limit )); then
		# Purge old entries
		for k in "${!lastseen[@]}"; do
			if (( now - lastseen[\$k] > limit )); then
				unset -v 'lastseen[$k]'
			fi
		done
		lastclean="${now}"
	fi
done