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md_src_plugins_mathcheck_README(3elektra) Elektra md_src_plugins_mathcheck_README(3elektra)

NAME

md_src_plugins_mathcheck_README - README

  • infos = Information about the mathcheck plugin is in keys below
  • infos/author = Thomas Waser thomas.waser@libelektra.org
  • infos/licence = BSD
  • infos/needs =
  • infos/provides = check
  • infos/placements = presetstorage
  • infos/description =

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.

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:

    kdb mount mathcheck.dump /example/mathcheck dump mathcheck
    kdb set user/example/mathcheck/a 3.1
    kdb set user/example/mathcheck/b 4.5
    kdb set user/example/mathcheck/k 7.6
    kdb setmeta user/example/mathcheck/k check/math "== + a b"
    kdb set user/example/mathcheck/k 7.7   # fails

To calculate values on-demand you can use:

    kdb setmeta user/example/mathcheck/k check/math ":= + a b"
    kdb get user/example/mathcheck/k       # 12.5
    kdb set user/example/mathcheck/a 5.5
    kdb get user/example/mathcheck/k       # 10

It also works with constants:

    kdb setmeta user/example/mathcheck/k check/math ":= + a '5'"
    kdb get user/example/mathcheck/k       # 10.5
    kdb set user/example/mathcheck/a 8.0
    kdb get user/example/mathcheck/k       # 13
Sun May 29 2016 Version 0.8.14