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  • infos = Information about validation plugin is in keys below
  • infos/author = Markus Raab elektra@libelektra.org
  • infos/licence = BSD
  • infos/provides = check
  • infos/needs =
  • infos/placements = presetstorage
  • infos/status = maintained unittest nodep libc
  • infos/metadata = check/validation check/validation/message check/validation/ignorecase check/validation/match check/validation/invert check/validation/type
  • infos/description = Validates key values using regular expressions


This plugin is a check plugin which checks string values of Keys using regular expressions.


The validation plugin looks for two metakeys. check/validation gives a regular expression to check against. If it is present, check/validation/message may contain an optional humanly readable message that will be passed with the error information.

Important: To validate against the whole string, you have to start the regular expression with ^ and end it with $. Otherwise expressions that e.g. match the empty string, always return true. Alternatively, you can use check/validation/match=LINE.


Metadata can be supplied to configure the validation:

  • check/validation/match: You can check against LINE, WORD or ANY
  • check/validation/ignorecase: If you want to ignore case.
  • check/validation/invert: If you want to invert match.


The implementation consists of a loop checking for every key if it has the mentioned metakey. The check itself is done by the POSIX regular expression library with the interface regcomp, regexec, regerror and regfree. The flag REG_EXTENDED is passed so that the regular expression will be compiled as an extended regular expression. REG_NOSUB gives a better performance and subexpressions cannot be used in this setup anyway.

Exported Methods

The plugin also exports the function ksLookupRE() that does a lookup in a KeySet using a regular expression. It starts from the current cursor of the KeySet and stops when the first value matches. Finally, this key is returned.