Re: Is there a way to increment the time for n seconds?

[H . J . Lu]

On Tue, Sep 11, 2001 at 03:00:15PM -0600, Bob Proulx wrote:
> H.J.
> 
> > Is there a way to increment the time for n seconds? I am thinking something 
> > like
> > 
> > # touch -F n foo
> > 
> > which will increment the time by n seconds and
> > 
> > # touch -B n foo
> > 
> > which will decrement the time by n seconds.
> 
> When you say increment, do you mean of the clock time or of the file
> timestamp time?  I will assume you mean filestamp time.  And of course

I meant the timestamp on the file.

> I am curious as to your application for this.

I have a source file, foo.p, and I do

# gen -o foo.c foo.p

which generates foo.c from foo.p. foo.p can be changed by other people
with the timestamp when the changed is made. I'd like to

# gen -o foo.c foo.p
# touch -r foo.p -F 1 foo.c

so that foo.c will be 1 second newer than foo.p. When foo.p is updated
with the timestamp when the change was made, foo.c will be older than
foo.p.

> 
> Since you suggested incrementing and decrementing by seconds I assume
> seconds as well.  But check out the date string parsing capability of
> both date and touch for more ideas.  You can do some very fun things
> using GNU extensions.  Try these.  Every time this command sequence is
> called it will increment the timestamp of the file.
> 
>   oldstamp=$(date -r foo +%s)
>   newstamp=$(expr $oldstamp + 10)
>   newtime=$(date -u -d "1970-01-01 $newstamp sec UTC")
>   touch --date="$newtime" foo
> 
> And of course the entire thing can be compressed into one line.
> 
>   touch --date="$(date -u -d "1970-01-01 $(expr $(date -r foo +%s) + 10) sec 
> UTC")" foo
> 

That may do the trick. But would it be easier to do just

# touch -F 10 foo


H.J.