# Logical tests

Logical tests feature (implemented in WPKG 0.9.6) allows nested checks:

<check type="logical" condition="or">
<check type="file" condition="exists" path="c:\fileA"/>
<check type="file" condition="exists" path="c:\fileB"/>
</check>


I.e. the outer check will return 'true' if either c:\fileA or c:\fileB exist. Nests within nests are acceptable.

New tests which have been added:

• not - returns the inverse of the nested check. Fails with an error if the number of nested checks is not one.
• and - returns the logical 'and' of all the nested checks. (See note below about lazy execution.)
• or - returns the logical 'or' of all the nested checks. (See note below about lazy execution.)
• atleast - returns true if at least one value of the nested checks are true. (See note below about lazy execution.)
• atmost - returns true if no more than value of the nested checks are true. (See note below about lazy execution.)

N.B - this test uses 'lazy execution' meaning that if the logical condition is already determined by one of the sub-checks, the other sub-checks will not be performed. For example, we might want to check that c:\Program Files\Application exists and that c:\Program Files\Application\App.exe also exists. If a test finds that the directory doesn't exist, there's no way that the result of the logical 'and' can be true so it returns false immediately. In the above example (c:\fileA, c:\fileB), if c:\fileA exists no test is performed for c:\fileB. Likewise, if an 'at least' test requires four of eight tests to pass, the routine returns 'true' as soon as it finds a fourth true check whether or not it has attempted all of them.

# Other examples

## two alternative entries in "Software Add/Remove"

Firefox can have a different entry in "Software Add/Remove":

• if version 2.0 was installed first, and then updated to 2.0.0.2, version shown will be still 2.0
• if version 2.0.0.2 was installed first, version shown will be 2.0.0.2
<check type="logical" condition="or">
<check type="uninstall" condition="exists" path="Mozilla Firefox (2.0)" />
<check type="uninstall" condition="exists" path="Mozilla Firefox (2.0.0.2)" />
</check>


## checking for a non existing file

Sometimes, it might be useful to use WPKG to actually remove the things (i.e., some useless addon/ads installed by the PC vendor).

Below, a check for an imaginary "remove-crapware" package.

We want to run the it only if the files are still on the drive (that is, a useless addon/ads are still installed by the PC vendor); if the files are not there anymore, the test is successful (this means, the removal was successful).

<check type='logical' condition='not' >
<check type='file' condition='exists' path='c:\foo\bar' />
</check>