Unix command

[neilm]

Is it safe to use:
TZ=+24 date

Basically this outputs yesterdays date, just wondering is it safe for leap years, new years, and all that?

(PS. Dunno how to unattach code so ignore the below)

 

[kamper]

First of all, I think that will be highly dependent on your platform. On osx, setting TZ=+# seems to output the current date UTC, regardless of what # is. On openbsd it makes the adjustment as you might expect.

But you also have to take into account that this only really works in UTC. To get yesterday's date here (Ontario) I have to use TZ=+29, but I don't think that'll work the other half of the year (I think it should be +30, but I haven't thought about it long enough).

 

[neilm]

I don't have the GNU date at work, so forced to come up with an alternative solution.

When you talk about daylight savings, where you have to up the hour the next half a year, I don't get it? Surely you can amend the TZ=+# to be anywhere in the 24hour period, no?

 

[Nothinman]

Are you stuck using shell? Date manipulation isn't too bad in perl so that might be an option.

 

[kamper]

Originally posted by: neilm
When you talk about daylight savings, where you have to up the hour the next half a year, I don't get it? Surely you can amend the TZ=+# to be anywhere in the 24hour period, no?

Sure, but do you want to amend it every 6 months?

 

[jfall]

this is much easier:

date -d "1 day ago"


BSD?

YESTERDAY=`expr \`date +%s\` - 86400`
date -r $YESTERDAY


edit, no gnu date

 

[neilm]

Originally posted by: kamper

Originally posted by: neilm
When you talk about daylight savings, where you have to up the hour the next half a year, I don't get it? Surely you can amend the TZ=+# to be anywhere in the 24hour period, no?

Sure, but do you want to amend it every 6 months?

That's what I mean, I don't get why you would have too.

Why not just keep it inline with timezone like so:
TZ=EST+29 date

...and use a cronjob to trigger it during the mid day? Not sure how timezone can affect the date, can someone explain?

Originally posted by: jfall
this is much easier:

date -d "1 day ago"


BSD?

YESTERDAY=`expr \`date +%s\` - 86400`
date -r $YESTERDAY


edit, no gnu date

Can't use any of those unfortunately, or this would be wee buns.

Originally posted by: Nothinman
Are you stuck using shell? Date manipulation isn't too bad in perl so that might be an option.

Yep I can use perl, and I think that would be a better alternative.

 

[kamper]

Originally posted by: neilm

Originally posted by: kamper

Originally posted by: neilm
When you talk about daylight savings, where you have to up the hour the next half a year, I don't get it? Surely you can amend the TZ=+# to be anywhere in the 24hour period, no?

Sure, but do you want to amend it every 6 months?

That's what I mean, I don't get why you would have too.

Why not just keep it inline with timezone like so:
TZ=EST+29 date

...and use a cronjob to trigger it during the mid day? Not sure how timezone can affect the date, can someone explain?

I'm probably just confused about this, but am I not 5 hours off UTC in the winter and 6 hours off in the summer? Isn't that the whole point of daylight savings time? I always get very confused when programming with dates.