Re: SECONDS=0 does not reset SECONDS, or I'm missing something

[Pier Paolo Grassi]

     [[ SECONDS -gt 0 ]] && sleep "$SECONDS"

you are missing a $ sigil here, it should be:

     [[ $SECONDS -gt 0 ]] && sleep "$SECONDS"

Il giorno gio 4 giu 2020 alle 12:14 Andreas Kusalananda Kähäri <
andreas.kahari@abc.se> ha scritto:

> I wrote a small script to delete many hundreds of thousands of files
> off a very slow disk.  The script is executed from find(1) and is
> given pathnames of directories to delete as arguments.  If a directory
> takes a second or more to delete a directory, the script sleeps for
> the amount of time it took to delete that directory before proceeding,
> in an attempt to let the filesystem sync metadata (this may have been
> misguided but it's not really important).
>
>         #!/usr/local/bin/bash -x
>
>         for name do
>                 SECONDS=0
>                 rm -r -f "$name"
>                 [[ SECONDS -gt 0 ]] && sleep "$SECONDS"
>         done
>
> What I noticed was that the script would go to sleep for a second
> every second, even if the deletion of directories was quick.  This
> indicates that SECONDS=0 didn't properly reset the SECONDS timer.  Or,
> it indicates that the timer is set by the system's clock (the current
> second according to the current time), and that it is not a real "timer"
> at all.  Or, that I have misunderstood something about how SECONDS is
> supposed to work.  Or, all of the above (please confirm).
>
> A sample script (see below) reproduces this with a tight loop on macOS
> Catalina running "5.0.17(1)-release (x86_64-apple-darwin19.4.0)"
> (bash from Homebrew) and on OpenBSD 6.7 running "5.0.17(1)-release
> (x86_64-unknown-openbsd6.7)".
>
>         while true; do SECONDS=0; [[ SECONDS -gt 0 ]] && echo hi; done
>
> (will print "hi" more or less once a second, and possibly slightly less
> often occasionally)
>
> So, I don't know whether this is an error in the documentation, my
> understanding of it, or in how the SECONDS variable is set/managed
> internally by the shell.  I'm assuming I'm misunderstanding.
>
> For reference (from the bash manual):
>
>         SECONDS
>                Each time this parameter is referenced, the number
>                of seconds since shell invocation is returned.  If a
>                value is assigned to SECONDS, the value returned upon
>                subsequent references is the number of seconds since
>                the assignment plus the value assigned.  If SECONDS is
>                unset, it loses its special properties, even if it is
>                subsequently reset.
>
>
>
> --
> Andreas (Kusalananda) Kähäri
> SciLifeLab, NBIS, ICM
> Uppsala University, Sweden
>
> .
>
> --
Pier Paolo Grassi