Constant statement#

Outputs literal text. Supports escape sequences and optional JSON field formatting when an outname and format are specified. .. summary-end

This statement specifies constant text. It is primarily intended for text-based output so constant fragments, such as newlines, can be included. Example from the testbench:

template(name="outfmt" type="list") {
    property(name="$!usr!msgnum")
    constant(value="\n")
}

The following common escape sequences are recognized inside the constant text:

\\ – single backslash
\n – LF
\ooo – three octal digits representing a character (\101 is "A"). Exactly three digits must be given.
\xhh – two hexadecimal digits representing a character (\x41 is "A"). Exactly two digits must be given.

For the complete list, see Rsyslog Parameter String Constants.

The value parameter is parsed by the generic configuration parser and then interpreted again as template constant text. To output literal text that looks like a byte escape, escape the backslash for both layers. For example, constant(value="\\\\x41") emits literal \x41.

If an unsupported character follows a backslash, behavior is unpredictable.

When creating structured outputs, constant text without an outname parameter is ignored. To include constant data in the name/value tree, provide outname as shown:

template(name="outfmt" type="list") {
    property(name="$!usr!msgnum")
    constant(value="\n" outname="IWantThisInMyDB")
}

To generate a constant JSON field the format parameter can be used:

template(name="outfmt" type="list" option.jsonf="on") {
          property(outname="message" name="msg" format="jsonf")
          constant(outname="@version" value="1" format="jsonf")
}

Here the constant statement generates "@version":"1". Both value and format must be specified.

When you want dotted outname values to be emitted as nested objects, enable option.jsonftree="on" on the template instead of option.jsonf.

Parameters#

value – constant value to emit
outname – output field name for structured outputs
format – empty or jsonf

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