[SOLVED] Linux: How to round off the date() to nearest interval

Issue

I want to round down the minutes to the nearest 15 min interval i.e. 00,15,30,45. I'm currently doing the below:

echo $(date +'%Y/%m/%d/%H/')$((($(($(date +'%M') / 15))-0)*15))

But at the start of the hour between 1-14 minutes, I get "/2021/11/03/21/0" instead of 00.

Also, I'm not sure if this is the best way to do this. Are there any alternatives?

Solution

Would you please try the following:

mod=$(( 10#$(date +%M) \% 15 ))
date -d "-${mod} minutes" +%Y/%m/%d/%H/%M

• The variable mod holds the remainder of the minutes divided by 15.
• Then round down to the nearest 15 minute interval by subtracting mod.

[Edit]
The manpage of crontab says:

Percent-signs (%) in the command, unless escaped with backslash (), will be changed into newline characters, and all data after the first % will be sent to the command as standard input.

If you want to execute the command within crontab, please modify the command as:

mod=$(( 10#$(date +\%M) \% 15 ))
date -d "-${mod} minutes" +\%Y/\%m/\%d/\%H/\%M

[Edit2]
If you want to embed the code in crontab file, please add a line which look like:

0 12 * * * username bash -c 'mod=$(( 10#$(date +\%M) \% 15 )); DATEVAR=$(date -d "-${mod} minutes" +\%Y/\%m/\%d/\%H/\%M); write.sh "$DATEVAR"'

• Please modify the execution time/date and the username accordingly.
• The default shell to execute crontab command may be /bin/sh. Then you will need to explicitly switch it to /bin/bash to execute bash commands.
• My apology that a backslash in front of % 15 (modulo operation) was missing in my previous post.

Answered By - tshiono