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rc/sh/minutemaid

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#!/usr/bin/env dash
# YES_ZSH
# YES_BASH
# YES_DASH
minutemaid() { ### @-
### return 0 and/or execute a command if the current minute
### is divisible by a given number. note that a minute is
### relative to the seconds since the epoch, not the minute of the hour.
### this ensures that commands will run roughly every N minutes,
### regardless of the minute hand on the clock.
###
### ```
### # crontab usage:
### * * * * * minutemaid 9 ~/work/do_my_bidding # runs every nine minutes
### ```
local offset=0 name
while getopts 'o:h' name; do
case $name in
o) offset="$OPTARG";;
?) local fd=0
[ $name = h ] && fd=1 || fd=2
printf "%s\n" "usage: $0 [-o offset] {interval} [{command} [{args...}]]" >&$fd
[ $name = h ] && return 0 || return 1;;
esac
done
shift $((OPTIND-1))
local interval="${1:?no interval specified}"
shift
local sec="$(date +%s)"
local min="$((sec/60+offset))"
local mod="$((min%interval))"
if [ $# -gt 0 ]; then
[ $mod -ne 0 ] || "$@"
else
[ $mod -eq 0 ] && return 0 || return 1
fi
}
[ -n "${preload+-}" ] || minutemaid "$@"