Re: [Help-bash] how to set up a repeat check procedure?

[lina]

On Friday 30,December,2011 10:23 PM, Greg Wooledge wrote:
> On Fri, Dec 30, 2011 at 10:11:41PM +0800, lina wrote:
> > #!/bin/bash
> >
> > while [ 'qstat | grep REM | grep R' ];
> >      do sleep 10;
> > done
> >
> > ./rem_extend.sh
> There are some mistakes here.  The most important is that you messed
> up the quotes -- I believe you intended to use backquotes, not single
> quotes.  However, even if you fix those, there are still more mistakes.
> For example, any line that matches REM is also going to match R, so the
> second grep is pointless.  Moreover, if you're just trying to see whether
> a grep command matches something or not, you don't even *want* to quote
> it, or capture it, nor do you want to use a [ command in any way.
>
> I believe what you want is:
>
> while qstat | grep -q REM
>    do sleep 10
> done
>
> > Last time I left the computer to sleep, it's supposed to run the
> > following script in 2 hours,
> > but morning I found it's not.  kinda of totally sleep over?
> The way you wrote the code, the [ command *always* returned true, because
> you were checking the length of a string literal.
>
>    while [ 'qstat | grep REM | grep R' ]
I do have lots to learn, I wished to grep " R " at that time, didn't 
realize such mistake.

-bash-3.2$ while [ ! qstat | grep -q nvt_em_16 ]; do echo finished ; 
done; echo running
-bash: [: missing `]'
grep: ]: No such file or directory
running

Before due to above error report, so I added the ' ', thanks for 
pointing out the mistakes.
I am still lack of understanding above error report,

Your way works,
-bash-3.2$ while  ! qstat | grep -q nvt_em_16 | grep R ; do echo 
finished ; done; echo running
running

suppose I have a bit long conditions, do I also no need [ ] for while?
$ while  ! qstat | grep -q nvt_em_16 &&  2 -lt 4 && 1; do echo finished 
; done; echo running
running

I tried, seems works?!

Sorry and thanks,
> is exactly equivalent to:
>
>   while [ 'HASKJDKHASKDHKJSAHDHSKJAHDHASLD' ]
>
> which is exactly equivalent to:
>
>    while true
>
> You were not running qstat or grep at all.
Best regards,