ASH get date 7 days agao

Hello.

In my bash scripts I can do:

DAY7=`date -I -d "7 days ago"`

When doing this in ash on my synology diskstation I get:

date: invalid date '7 days ago'


Is there any other way to do this that would work on ash?
pucko73Asked:
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simon3270Connect With a Mentor Commented:
I think it's not the shell, it's that your "date" command on your diskstation doesn't have the GNU extensiosn such as "7 days ago".

if you can use Perl, how about:
perl -MPOSIX -e 'print POSIX:strftime("%Y-%m-%d\n", localtime(time-(7*24*60*60)))'

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(with the caveat that this doesn't necessarily cope in the week that daylight savings starts and stops, if it is called just before or after midnight)
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pucko73Author Commented:
date -- help shows:

-d,--date TIME  Display TIME, not 'now'
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Joseph GanSystem AdminCommented:
ash is very limited, it doesn't support additional functionality as bash does.
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pucko73Author Commented:
[admin@DiskStation admin]$ perl -MPOSIX -e 'print POSIX:strftime("%Y-%m-%d\n", l
ocaltime(time-(7*24*60*60)))'
syntax error at -e line 1, near "POSIX:"
Execution of -e aborted due to compilation errors.
[admin@DiskStation admin]$
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simon3270Commented:
Ah, that's what comes of trying to write and test the code on one machine, and copy it to another!

There should be two colons in POSIX::strftime, so the whole line is:
$ perl -MPOSIX -e 'print POSIX::strftime("%Y-%m-%d\n", localtime(time-(7*24*60*60)))'
2013-12-09
$ date
Mon Dec 16 22:20:18 GMT 2013
$ 

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