rsyslog

The rocket-fast system for log processing

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Expressions

The language supports arbitrary complex expressions. All usual operators are supported. The precedence of operations is as follows (with operations being higher in the list being carried out before those lower in the list, e.g. multiplications are done before additions.

  • expressions in parenthesis
  • not, unary minus
  • *, /, % (modulus, as in C)
  • +, -, & (string concatenation)
  • ==, !=, <>, <, >, <=, >=, contains (strings!), startswith (strings!)
  • and
  • or

For example, “not a == b” probably returns not what you intended. The script processor will first evaluate “not a” and then compare the resulting boolean to the value of b. What you probably intended to do is “not (a == b)”. And if you just want to test for inequality, we highly suggest to use “!=” or “<>”. Both are exactly the same and are provided so that you can pick whichever you like best. So inquality of a and b should be tested as “a <> b”. The “not” operator should be reserved to cases where it actually is needed to form a complex boolean expression. In those cases, parenthesis are highly recommended.

See also

Help with configuring/using Rsyslog:

  • Mailing list - best route for general questions
  • GitHub: rsyslog source project - detailed questions, reporting issues that are believed to be bugs with Rsyslog
  • Stack Exchange (View, Ask) - experimental support from rsyslog community

See also

Contributing to Rsyslog:

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