Plugin: conditionals

• infos = Information about the conditionals plugin is in keys below
• infos/author = Thomas Waser thoma.nosp@m.s.wa.nosp@m.ser@l.nosp@m.ibel.nosp@m.ektra.nosp@m..org
• infos/licence = BSD
• infos/provides =
• infos/needs =
• infos/recommends =
• infos/placements = postgetstorage presetstorage
• infos/status = unittest nodep libc global preview
• infos/metadata = check/condition assign/condition condition/validsuffix check/condition/any/# check/condition/all/# check/condition/none/# assign/condition/#
• infos/description = ensures key values through conditions

Introduction

This plugin uses if-then-else like conditions. It also works as global plugin.

Installation

See installation. The package is called libelektra5-extra.

Check Syntax

Stored in the metakey check/condition to validate data is:

(IF-condition) ? (THEN-condition) : (ELSE-condition) where the ELSE-condition is optional

Condition: Key Operation ‘('String’ | '1234.56' | Key | '')`

Operations: !=, ==, <, <=, =>, >, :=, where:

• := is used to set a key value
• others are for comparison as in C

Testing if Key Exists

(! a/key) evaluates to true if the key a/key doesn't exist, to false if it exists.

Assign Syntax

(IF-condition) ? ('ThenValue') : ('ElseValue')

Depending on if the condition is met, either 'ThenValue' or 'ElseValue' will be assigned as key value if the metakey assign/condition is used.

Experimental: Nested Conditions

Multiple conditions can be nested and combined using parentheses and && (logical AND) or || (logical OR). Additional parentheses must be used to form valid conditions again. ( (condition 1) && (condition 2) )

Valid Suffix

The condition/validsuffix can be used to define a list of valid suffixes to numeric values. If two operants have the same valid suffix or one of them no suffix they will be treated by their numeric value ignoring their suffix. ‘condition/validsuffix = 'm’, 'cm', 'km'would treat2.3mjust as the numeric value2.3` when comparing to another value having the same or no suffix.

Keynames

Keynames are all either relative to to-be-tested key (starting with ./ or ../), relative to the parentkey (starting with @/) or absolute (e.g. system:/key).

Multiple Statements

It's also possible to test multiple conditions using check/condition/{any,all,none} as a meta array. Where any means that at least one statement has to evaluate to true, all that all statements have to evaluate to true, and none that no statement is allowed to evaluate to false (default). For multiple assign statements use assign/condition as a meta array. The first assign/condition/# statement that evaluates to true will be assigned and the rest ignored.

Example

(this/key  != 'value') ? (then/key == some/other/key) : (or/key <= '125')

Meaning: IF this/key NOT EQUAL TO ‘'value’THENthen/keyMUST EQUALsome/other/keyELSEor/keyMUST BE LESS THAN125`

Another full example:

#Backup-and-Restore:user:/tests/conditionals
 
sudo kdb mount conditionals.dump user:/tests/conditionals conditionals dump
 
kdb set user:/tests/conditionals/fkey 3.0
kdb set user:/tests/conditionals/hkey hello
 
# will succeed
kdb meta-set user:/tests/conditionals/key check/condition "(../hkey == 'hello') ? (../fkey == '3.0')"
 
# will fail
kdb meta-set user:/tests/conditionals/key check/condition "(../hkey == 'hello') ? (../fkey == '5.0')"
# RET:5
# ERROR:C03200

Assignment example:

kdb set user:/tests/conditionals/hkey Hello
kdb meta-set user:/tests/conditionals/hkey assign/condition "(./ == 'Hello') ? ('World')"
# alternative syntax: "(../hkey == 'Hello') ? ('World')
 
kdb get user:/tests/conditionals/hkey
#> World
 
# cleanup
kdb rm -r user:/tests/conditionals
sudo kdb umount user:/tests/conditionals

Global plugin example:

# Backup old list of global plugins
kdb set user:/tests/msr $(mktemp)
kdb export system:/elektra/globalplugins > $(kdb get user:/tests/msr)
 
sudo kdb mount main.ini /tests/conditionals ni
sudo kdb mount sub.ini /tests/conditionals/sub ni
 
# mount conditionals as global plugin
sudo kdb global-mount conditionals || $(exit 0)
 
# create testfiles
echo 'key1=val1'                                               >  `kdb file /tests/conditionals`
echo '[key1]'                                                    >> `kdb file /tests/conditionals`
echo "check/condition=(./ == 'val1') ? (../sub/key == 'true')" >> `kdb file /tests/conditionals`
 
echo "key=false" > `kdb file /tests/conditionals/sub`
 
# should fail and yield an error
kdb export /tests/conditionals ni
# ERROR:C03200
# Sorry, module conditionals issued the error C03200:
# Validation failed: Validation of Key key1: (./ == 'val1') ? (../sub/key == 'true') failed. ((../sub/key == 'true') failed)
 
kdb set /tests/conditionals/sub/key true
 
# should succeed
kdb export /tests/conditionals ni
 
# cleanup
kdb rm -r /tests/conditionals
sudo kdb umount /tests/conditionals/sub
sudo kdb umount /tests/conditionals
 
sudo kdb global-umount conditionals
 
kdb rm -r system:/elektra/globalplugins
kdb import system:/elektra/globalplugins < $(kdb get user:/tests/msr)
rm $(kdb get user:/tests/msr)
kdb rm user:/tests/msr