Elektra: Plugin: mathcheck

Elektra 0.8.24

Plugin: mathcheck

- infos = Information about the mathcheck 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 = check
- infos/needs =
- infos/placements = presetstorage
- infos/status = maintained unittest shelltest nodep discouraged
- infos/metadata = check/math
- infos/description = validates a set of keys through a mathematical expression

Compares a key value to a mathematical expression using polish prefix notation defined in the `check/math` metakey. Operations are `+ - / *` . Operants are keys with names relative to the parent key. How the values are compared is specified at the beginning of the metakey using the conditions `<, <=, ==, !=, =>, >, :=` `:=` is used to set key values. All values are interpreted as `double` floating point values.

### 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`).

## Examples

`check/math = "== + ../testval1 + ../testval2 ../testval3"` compares the keyvalue to the sum of testval1-3 and yields an error if the values are not equal. `check/math = "<= - @/testval1 * @/testval2 @/testval3"` tests if the keyvalue is less than or equal to testval1 - (testval2 * testval3) and yields an error if not.

Full example:

# Backup-and-Restore:/tests/mathcheck
sudo kdb mount mathcheck.dump /tests/mathcheck mathcheck
kdb set /tests/mathcheck/a 3.1
kdb set /tests/mathcheck/b 4.5
kdb set /tests/mathcheck/k 7.6
kdb setmeta user/tests/mathcheck/k check/math "== + ../a ../b"
# should fail
kdb set /tests/mathcheck/k 7.7
# RET:5
# ERROR:123
# Set string to "7.7"
# The command set failed while accessing the key database with the info:
# Error (#123) occurred!
# Description: invalid value
# Ingroup: plugin
# Module: mathcheck
# At: /home/thomas/Dev/Elektra/libelektra/src/plugins/mathcheck/mathcheck.c:399
# Reason: 7.7 != 7.6
# Mountpoint: /tests/mathcheck
# Configfile: /home/thomas/.config/mathcheck.dump.25680:1478749409.938013.tmp

To calculate values on-demand you can use:

kdb setmeta user/tests/mathcheck/k check/math ":= + @/a @/b"
kdb set /tests/mathcheck/a 8.0
kdb set /tests/mathcheck/b 4.5
kdb get /tests/mathcheck/k
#> 12.5
kdb set /tests/mathcheck/a 5.5
kdb get /tests/mathcheck/k
#> 10

It also works with constants:

kdb setmeta user/tests/mathcheck/k check/math ":= + ../a '5'"
kdb set /tests/mathcheck/a 5.5
kdb get /tests/mathcheck/k
#> 10.5
kdb set /tests/mathcheck/a 8.0
kdb get /tests/mathcheck/k
#> 13
#cleanup
kdb rm -r /tests/mathcheck
sudo kdb umount /tests/mathcheck