Bash script for time loop

Question

I am trying to write the code to convert the date to desired format and increase 300 seconds in every run.

Date is in form 2020-12-19 00:35:00+00:000 want it to be converted to form 2020-12-19T00:35:00Z and after every run increase add five minutes to the timestamp.

for run in $(seq 0 $REPEAT)
do
        echo "======================"
        VARIABLE=$( expr 300 '*' $run)
        DATE=$(date --iso-8601=seconds -d "2020-19-19T00:35:00 + $VARIABLE seconds")
        echo $DATE
        for file in ${FILELIST[@]};
        do

               echo "Running fine"
        done

done

But i am getting the output as:

2020-03-09T03:05:01+05:30

I want the output to be 2020-12-19T00:35:00Z then 2020-12-19T00:40:00Z and so on.

Poshi · Accepted Answer · 2020-05-08 08:20:45Z

1

Month number 19 does not exist. Try with following approach:

# Get the number of seconds since Epoch
secs=$(date +%s --date="2020-9-19T00:35:00")

for run in $(seq 0 $REPEAT)
do
    echo "======================"
    # Next increment
    VARIABLE=$((300*run))

    # Add the increment seconds and translate to the desired format
    DATE=$(date --iso-8601=seconds -d "@$((secs+VARIABLE))")

    echo $DATE
    for file in ${FILELIST[@]};
    do
        echo "Running fine"
    done
done

BTW, if you really want to have Z timezone, you will have to work a little bit the output format.

edited May 8, 2020 at 8:20

answered May 8, 2020 at 8:14

Poshi

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4 Comments

Socowi Over a year ago

Um, pretty sure that you can add seconds in date -d, at least with GNU date. date -d 'now + 3600 seconds' prints the date in one hour (=3600s) from now.

Poshi Over a year ago

You are right, @Socowi. I had some issue while trying to add this date and I assumed it was not possible. Input format for date is not easy.

Socowi Over a year ago

Yeah, you never know what -d accepts and what it rejects. Even after reading the (sparse) documentation I still have to guess and test what works and what doesn't.

Poshi Over a year ago

In fact, asking for "2020-9-19T00:35:00 + 1 second" does not work.

Socowi · Accepted Answer · 2020-05-29 08:37:00Z

As pointed out by Poshi your script used the date 2020-19-19 which does not exist. Once we fix that we are very close. There are only three things left to do:

-d "isoFormatWithoutTimezome + 3 seconds seems to be misinterpreted as
-d "(isoFormat withTimezone='+3') seconds". With this interpretation the trailing seconds doesn't really make sense but seems to add a single second to the date. To prevent false interpretation as a time zone specify the time zone after the date and before the + 3 seconds:
-d "2020-19-19T00:35:00Z + 3 seconds".
Setting the timezone for the output is possible with date's environment variable TZ. For UTC we can set the TZ to the empty string.
date -I shows UTC as +00:00 instead of Z. To change the output format we could either supply a custom date String +...Z or simply do a string replacement sed s/+00:00$/Z/.

By the way: The preferred naming convention for variables in bash is NOT ALLCAPS, as allcaps variables are by convention environment variables and have a high chance colliding with already existing environment variables.

#! /usr/bin/env bash

repeat=5 # does 6 repeats! (retained behavior from your original script) 
for ((run = 0; run <= repeat; run++)); do
    date=$(TZ= date -Is -d "2020-12-19T00:35:00Z + $((run * 300)) sec" | sed 's/+00:00$/Z/')
    echo "$date"

    # do stuff
done

prints

2020-12-19T00:35:00Z
2020-12-19T00:40:00Z
2020-12-19T00:45:00Z
2020-12-19T00:50:00Z
2020-12-19T00:55:00Z
2020-12-19T01:00:00Z

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