[syslog-ng] Pattern DB Parser "Default Values"

[Gergely Nagy]

David Hauck <davidh at netacquire.com> writes:

> I was wondering if there was a way to specify default values for
> pattern DB parsers that include a value, but where the parsed value is
> <null>[/empty]?
>
> In particular if I have something like the following:
>
>           <pattern>test message; field1=@ESTRING:field1: @field2=@ESTRING:field2: @field3=@ESTRING:: @field4=@ESTRING:field4: @</pattern>
>
> I'd like to be able to do something like either, 1:
>
>           <pattern>test message; field1=@ESTRING:field1<foo>: @field2=@ESTRING:field2<bar>: @field3=@ESTRING:: @field4=@ESTRING:field4<beef>: @</pattern>
>
> Or 2:
>
>           <pattern>test message; field1=@ESTRING:field1: @field2=@ESTRING:field2: @field3=@ESTRING:: @field4=@ESTRING:field4: @</pattern>
>         <values>
>           <value name="field1.default">foo</value>
>           <value name="field2.default">bar</value>
>           <value name="field4.default">beef</value>
>
> Just curious...

You can use ${field1:-foo} in templates, to set a default if none is
set. It doesn't work for empty fields, though, but that can be worked
around with an $(if $(length $field1) eq 0 "default" $field1) template,
possibly in a rewrite rule.

Though, maybe ${field1:-foo} should work for empty values too, not just
unset ones (to mimic shell better, which does just that). I can make it
do so, if that'd be desired, would make it unnecessary to use the $(if)
hack.

@Bazsi: What do you think?

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