I was working on a shell script last night and needed to calculate the value for yesterday. I did not have access to GNU date, so using that is out of the question. All I could use was what was available to me in a default install of Solaris 10. So I decided to use Perl as such (note that the YESTERDAY should all be on one line):
#!/bin/bash
YESTERDAY=$(perl -e '@y=localtime(time()-86400);
printf "%04d%02d%02d",$y[5]+1900,$y[4]+1,$y[3];$y[3];')
What this will do is store the value of yesterday in a shell variable called YESTERDAY
Now I have not done perl in a long while so here is an explanation of what it does:
1. Runs the perl function time which will find the current time, then subtract 86400 from it (24 hours).
2. Next it is run through the localtime function which creates an array that has the following values:
| Array Element | Value |
|---|---|
| 0 | Seconds |
| 1 | Minutes |
| 2 | Hour |
| 3 | Day of Month |
| 4 | Month of year (0=January) |
| 5 | Year (starting at 1900) |
| 6 | Day of week (0=sunday) |
| 7 | Day of Year (0..364 or 0..365 if leap) |
| 8 | Is Daylight savings time active |
So in my little script above, we are looking for fields 5, 4 and 3. I add 1900 to the value of 5 (in this case 5 = 108). I add 1 to the value of 4 to get the current month (3+1 = 4 = April). The values are then pushed through printf so that we have a 4 digit year with leading 0’s, a 2 digit month with leading 0’s and a 2 digit day with leading 0’s. So the value of my YESTERDAY variable will now show 20080418.
Hope this helps some one else.