On 23 July 2024 9:42:27 pm AEST, Greg Wooledge <g...@wooledge.org> wrote:
>On Tue, Jul 23, 2024 at 18:02:53 +1000, Keith Bainbridge wrote:
>> From the tab I had used earlier, ran source .bashrc
>>
>> then
>> :/tmp/205.2024 $> mkcd /tmp/day$DOYR.$YEAR
>
>So you're setting those variables one time inside your .bashrc file?
The variables are in .bashrc. I believed that was a good place to keep them.
I'll check the original tomorrow, but it looks like a couple are there by
default
I intended to list all variables in my original note. Seems I need to put them
else where
>
>This is quite bad. What happens when you have a terminal window that
>you open before midnight, and then continue using *after* midnight?
>Those variables will still be set to the previous day's values.
The day# in my command prompt increments when I start in the morning. Maybe I
need to press enter. I'll check tomorrow and confirm
>
>Also, why did you start three separate threads for this question?
I wasn't aware I had started new threads. I realised as soon as I read that
comment, that all I had to do was reply to group with the addenda
>
>> So, now question is how can I get cron to 'source .bashrc' I'm thinking
>> add that line to my script?
>
>I would advise against it. Who knows what kind of silly things your
>.bashrc may do that you wouldn't want an automated script to pick up.
>Even if you verify that your .bashrc is "cron safe" right now, you
>might add something to it a year from now, forgetting that you need
>it to remain "cron safe", and accidentally break the script.
>
>Any command that's supposed to act based on the current day will need
>to perform its *own* request to fetch the current day from the system
>clock. It cannot rely on an environment variable set some unknown
>length of time in the past.
>
>Use the date command or bash's printf %()T inside your bash script to
>get the current date.
Right ooo
>
>Moreover, never make *two* calls to the system clock in the same script.
>If you need the Julian day number (%j) and also the calendar
>day-of-the-month number (%d), don't do this:
>
> # WRONG
> julian=$(date +%j)
> dom=$(date +%d)
>
>That calls out to the system clock twice, and gets two different values.
>If the script is executed right at midnight, you might get two different
>days.
>
>Instead, only make *one* call. There are a couple different ways to do
>this. One is to get all the date(1) fields you need at once, and then
>parse them out:
>
> read -r julian dom < <(date "+%j %d")
>
>Another is to fetch the epoch time value (%s) and then use that value
>in all future calls. With GNU date:
>
> now=$(date +%s)
> julian=$(date -d "@$now" +%j)
> dom=$(date -d "@$now" +%d)
>
>Or with bash's printf, on Linux or BSD:
>
> printf -v now '%(%s)T' -1
> printf -v julian '%(%j)T' "$now"
> printf -v dom '%(%d)T' "$now"
>
>(Bash 5.0 added an EPOCHSECONDS variable as well.)
>
>This same concept applies in any programming language you use. It's not
>just a shell script thing, even though I'm showing shell script examples
>here.
>
Just quickly, from my tablet
More in the morning.
--
All the best
Keith BAINBRIDGE
+61 447 667 468
keithr...@gmail.com
keith.bainbridge.3...@mail.com
GMT + 10
From my Apad
