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 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:/examples/mathcheck
 kdb mount mathcheck.dump /examples/mathcheck dump mathcheck
 kdb set /examples/mathcheck/a 3.1
 kdb set /examples/mathcheck/b 4.5
 kdb set /examples/mathcheck/k 7.6
 kdb setmeta user/examples/mathcheck/k check/math "== + ../a ../b"
 # should fail
 kdb set /examples/mathcheck/k 7.7
 # RET:5
 # ERRORS: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: /examples/mathcheck
 # Configfile: /home/thomas/.config/mathcheck.dump.25680:1478749409.938013.tmp
 kdb rm -r /examples/mathcheck
 kdb umount /examples/mathcheck

To calculate values on-demand you can use:

 # Backup-and-Restore:/examples/mathcheck
 kdb mount mathcheck.dump /examples/mathcheck dump mathcheck
 kdb setmeta user/examples/mathcheck/k check/math ":= + @/a @/b"
 kdb set /examples/mathcheck/a 8.0
 kdb set /examples/mathcheck/b 4.5
 kdb get /examples/mathcheck/k
 12.5
 kdb set /examples/mathcheck/a 5.5
 kdb get /examples/mathcheck/k
 10
 kdb rm -r /examples/mathcheck
 kdb umount /examples/mathcheck

It also works with constants:

 # Backup-and-Restore:/examples/mathcheck
 kdb mount mathcheck.dump /examples/mathcheck dump mathcheck
 kdb setmeta user/examples/mathcheck/k check/math ":= + ../a '5'"
 kdb set /examples/mathcheck/a 5.5
 kdb get /examples/mathcheck/k
 10.5
 kdb set /examples/mathcheck/a 8.0
 kdb get /examples/mathcheck/k
 13
 kdb rm -r /examples/mathcheck
 kdb umount /examples/mathcheck