F18, F19 webalizer problem?

[Cristian Sava]

Hi all,

Webalizer is enabled via /etc/sysconfig/webalizer but I don't understand
why /etc/cron.daily/00webalizer has this line:

[ "z$WEBALIZER_CRON" != "zyes" ] && exit 0

that I think it should be (and it is working this way)

[ "$WEBALIZER_CRON" != "yes" ] && exit 0

What is the mistery?

C.Sava

[Patrick O'Callaghan]

On Fri, 2013-04-26 at 15:36 +0300, Cristian Sava wrote:
> Hi all,
>
> Webalizer is enabled via /etc/sysconfig/webalizer but I don't understand
> why /etc/cron.daily/00webalizer has this line:
>
> [ "z$WEBALIZER_CRON" != "zyes" ] && exit 0
>
> that I think it should be (and it is working this way)
>
> [ "$WEBALIZER_CRON" != "yes" ] && exit 0
>
> What is the mistery?

The "z$Foo" != "zbar" style is idiomatic in Shell scripts. I think it's
to ensure portability between Shells with slightly different expression
rules.

poc

[Cristian Sava]

On Fri, 2013-04-26 at 09:12 -0430, Patrick O'Callaghan wrote:
> On Fri, 2013-04-26 at 15:36 +0300, Cristian Sava wrote:
> > Hi all,
> >
> > Webalizer is enabled via /etc/sysconfig/webalizer but I don't understand
> > why /etc/cron.daily/00webalizer has this line:
> >
> > [ "z$WEBALIZER_CRON" != "zyes" ] && exit 0
> >
> > that I think it should be (and it is working this way)
> >
> > [ "$WEBALIZER_CRON" != "yes" ] && exit 0
> >
> > What is the mistery?
>
> The "z$Foo" != "zbar" style is idiomatic in Shell scripts. I think it's
> to ensure portability between Shells with slightly different expression
> rules.
>
> poc

Thank you very much.

C.Sava

[Cameron Simpson]

On 26Apr2013 09:12, Patrick O'Callaghan  wrote:
| On Fri, 2013-04-26 at 15:36 +0300, Cristian Sava wrote:
| > Webalizer is enabled via /etc/sysconfig/webalizer but I don't understand
| > why /etc/cron.daily/00webalizer has this line:
| > 
| > [ "z$WEBALIZER_CRON" != "zyes" ] && exit 0
| > 
| > that I think it should be (and it is working this way)
| > 
| > [ "$WEBALIZER_CRON" != "yes" ] && exit 0
| > 
| > What is the mistery?
| 
| The "z$Foo" != "zbar" style is idiomatic in Shell scripts. I think it's
| to ensure portability between Shells with slightly different expression
| rules.

In particular it avoids issues where $WEBALIZER_CRON looks like a test
operator such as "-z" or something unfortunate.

[Mike Wright]

04/27/2013 03:49 PM, Cameron Simpson wrote:
> On 26Apr2013 09:12, Patrick O'Callaghan  wrote:
> | On Fri, 2013-04-26 at 15:36 +0300, Cristian Sava wrote:
> | > Webalizer is enabled via /etc/sysconfig/webalizer but I don't understand
> | > why /etc/cron.daily/00webalizer has this line:
> | >
> | > [ "z$WEBALIZER_CRON" != "zyes" ] && exit 0
> | >
> | > that I think it should be (and it is working this way)
> | >
> | > [ "$WEBALIZER_CRON" != "yes" ] && exit 0
> | >
> | > What is the mistery?
> |
> | The "z$Foo" != "zbar" style is idiomatic in Shell scripts. I think it's
> | to ensure portability between Shells with slightly different expression
> | rules.
>
> In particular it avoids issues where $WEBALIZER_CRON looks like a test
> operator such as "-z" or something unfortunate.

Also there may be situations where $SOME_VAR evaluates to null.  Then a 
test looks like [ != "something" ] which is guaranteed to break.  By 
(pre|post)fixing each side with an arbitrary character such as Z that 
same scenario would yield [ "Z" != "Zsomething" ] and would survive 
shell parsing.

[Cameron Simpson]

On 27Apr2013 16:41, Mike Wright  wrote:
| 04/27/2013 03:49 PM, Cameron Simpson wrote:
| >On 26Apr2013 09:12, Patrick O'Callaghan  wrote:
| >| On Fri, 2013-04-26 at 15:36 +0300, Cristian Sava wrote:
| >| > [ "z$WEBALIZER_CRON" != "zyes" ] && exit 0
[...]
| >| The "z$Foo" != "zbar" style is idiomatic in Shell scripts. I think it's
| >| to ensure portability between Shells with slightly different expression
| >| rules.
| >
| >In particular it avoids issues where $WEBALIZER_CRON looks like a test
| >operator such as "-z" or something unfortunate.
| 
| Also there may be situations where $SOME_VAR evaluates to null.
| Then a test looks like [ != "something" ] which is guaranteed to
| break.

It's quoted. That will stop it vanishing.