
\begin{DoxyItemize}
\item infos = Information about the mathcheck plugin is in keys below
\item infos/author = Thomas Waser \href{mailto:thomas.waser@libelektra.org}{\tt thomas.\+waser@libelektra.\+org}
\item infos/licence = B\+SD
\item infos/provides = check
\item infos/needs =
\item infos/placements = presetstorage
\item infos/status = maintained unittest shelltest nodep discouraged
\item infos/metadata = check/math
\item infos/description = validates a set of keys through a mathematical expression
\end{DoxyItemize}

Compares a key value to a mathematical expression using polish prefix notation defined in the {\ttfamily check/math} metakey. Operations are {\ttfamily + -\/ / $\ast$} . 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 {\ttfamily $<$, $<$=, ==, !=, =$>$, $>$, \+:=} {\ttfamily \+:=} is used to set key values. All values are interpreted as {\ttfamily double} floating point values.

\subsubsection*{Keynames}

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

\subsection*{Examples}

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

Full example\+: 
\begin{DoxyCode}
# Backup-and-Restore:/examples/mathcheck

sudo 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
\end{DoxyCode}
 To calculate values on-\/demand you can use\+: 
\begin{DoxyCode}
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
\end{DoxyCode}
 It also works with constants\+: 
\begin{DoxyCode}
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

#cleanup
kdb rm -r /examples/mathcheck
sudo kdb umount /examples/mathcheck
\end{DoxyCode}
 