Technical data

8. Documentation for Developers

Expansion of Existing Regular Expressions

If an optional package adds an additional value for a variable which will be examined by a

regular expression, then the regular expression has to be expanded. This is done simply by

deﬁning the new possible values by a regular expression (as described above) and complement

the existing regular expression in a separate check/<PACKAGE>.exp ﬁle. That an existing

expression is modiﬁed is indicated by a leading “+”. The new expression complements the

existing expression by appending the new value to the existing value(s) as an alternative. If

another expression makes use of the complemented expression, the supplement is also there.

The speciﬁed error message is simply appended to the end of the existing one.

Using the Ethernet driver as an example this could look like here:

• The base packages provides a lot of Ethernet drivers and checks the variable NET_DRV_x

using the regular expression NET_DRV, which is deﬁned as follows:

NET_DRV = '3c503|3c505|3c507|...'

: 'invalid ethernet driver, please choose one'

' of the drivers in config/base.txt'

• The package “pcmcia” provides additional device drivers, and hence has to complement

NET_DRV. This is done as follows:

PCMCIA_NET_DRV = 'pcnet_cs|xirc2ps_cs|3c574_cs|...' : ''

+NET_DRV = '(RE:PCMCIA_NET_DRV)' : ''

Now PCMCIA drivers can be chosen in addition.

Extend Regular Expressions in Relation to YESNO Variables

If you have extended NET_DRV with the PCMCIA drivers as shown above, but the package

“pcmcia” has been deactivated, you still could select a PCMCIA driver in config/base.txt

without an error message generated when creating the archives. To prevent this, you may

let the regular expression depend on a YESNO variable in the conﬁguration. For this purpose,

the name of the variable that determines whether the expression is extended is added with

brackets immediately after the name of the expression. If the variable is active and has the

value “yes”, the term is extended, otherwise not.

PCMCIA_NET_DRV = 'pcnet_cs|xirc2ps_cs|3c574_cs|...' : ''

+NET_DRV(OPT_PCMCIA) = '(RE:PCMCIA_NET_DRV)' : ''

If specifying OPT_PCMCIA='no' and using i.e. the PCMCIA driver xirc2ps_cs in

config/base.txt, an error message will be generated during archive build.

Hint: This does not work if the variable is not set explicitely in the conﬁguration ﬁle but

gets its value by a default setting in check/<PACKAGE>.txt. In this case the variable hence

has to be set explicitely and the default setting has to be avoided if necessary.

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