Creating a sequence with _ in the number

Question

Hey I feel like I am probably being a little stupid but I cannot seem to find anywhere how to utilize a sequence with symbol in it.

I want to be able to run a sequence from two date and times: 20191110_2330 and 20191111_0200 but I cannot work out how to read over the _. Any advice would be greatly appreciated.

Answer 1

Possibly overkill but I was able to accomplish this with the following bash function and GNU date(1):

seq_dates () {
    local Y1 M1 D1 d1
    local r
    local m=0
    Y1=${1:0:4}
    M1=${1:4:2}
    D1=${1:6:2}
    d1="${Y1}-${M1}-${D1} ${1: -4}"
    until [[ $r == $2 ]]; do
        r=$($date -d "$d1 + $m minutes" '+%Y%m%d_%H%M')
        printf '%s\n' "$r"
        ((m++))
    done
}

You would call it like:

seq_dates 20191110_2330 20191111_0200

It will convert the input start date into a format useable by GNU date and then runs a loop, adding 1 minute to the date each time until it is equal to the given end date.

Note: If the given end date falls before the given start date this will run an infinite loop.

Answer 2

For looping over dates, simply define start and end and loop over all desired time steps.

Just use epoch time for start and end and add 60 seconds or the desired step size at each iteration. Then set output format as desired.

#!/bin/bash
start=$(date -d2019-11-10T23:30 +%s)
end=$(date -d2019-11-11T02:00 +%s)
ddate="$start"

while [ $ddate -le $end ] ; do
   date -d@"$ddate" +%Y%m%d_%H%M
   ddate=$((ddate+60))
done

If you want to convert your date strings to a readable format for the date command, just use sed:

 echo 20191110_2030 | sed 's/\(....\)\(..\)\(..\)_\(..\)\(..\)/\1-\2-\3T\4:\5/'

Unfortunately most date-versions don't support defining the input string format.