VanLUG Email Archive
Ted Powell (ted@eslvcr.fireplug.net)
Tue, 20 Oct 1998 01:56:08 -0700
On Tue, Oct 20, 1998 at 01:20:14AM -0800, Ian Dobson wrote:
> [...]
> it just loops forever, shouldn't it exit at some point?
> [...]
> while [ $nostrobe=2 ]
> [...]
In a word, no.
You have a single argument inside the [ ] and the rule for a single
argument is that if and only if it is non-null, the result is "true".
Even if your $nostrobe evaluated to the null string, the `=' and the `2'
would still make your argument two bytes long and therefore non-null.
You will probably do better with the three-argument form of [ ]
while [ $nostrobe = 2 ]
which will give you the test for string equality you were probably
hoping for. Considering that grep -c gives a numeric result, your script
would be more clear if you used a numeric comparison
while [ $nostrobe -eq 2 ]
Note, by the way, that in
> nostrobe=`ps ax | grep -c "strobe"`
the grep command will sometimes show up in the output of the ps command,
and sometimes not. When it does, that line of ps output will match the
grep pattern
$ ps ax | grep 'strobe'
10759 p2 S 0:00 grep strobe
Whether the grep shows up in the output of the ps command really does
vary. Here are two consecutive runs looking for something I knew was
running
$ ps ax |grep named
312 ? S 0:48 named
$ ps ax |grep named
312 ? S 0:48 named
10765 p2 S 0:00 grep named
You may want to try something like
nostrobe=$(ps ax | grep strobe | grep -v grep | wc -l)
-- ted@psg.com http://psg.com/~ted/ (Ted Powell) If your hard drive crashes, perhaps you have a recent backup. If Earth crashes, what then? We need off-site backup: Luna, L5, Mars, wherever.
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