[[filter-syntax]]
Filter expression syntax
~~~~~~~~~~~~~~~~~~~~~~~~
-Filter expressions can be specified with the option:--filter option
-when creating a new event rule. If the filter expression evaluates
-to true when executed against the dynamic values of an event's fields
-when tracing, the filtering condition passes.
+A filter expression can be specified with the option:--filter option
+when creating a new event rule. If the filter expression evaluates to
+true when executed against the dynamic values of an event's fields when
+tracing, the filtering condition passes.
NOTE: Make sure to **single-quote** the filter expression when running
the command from a shell, as filter expressions typically include
The precedence table of the operators above is the same as the one of
the C language. Parentheses are supported to bypass this.
-The dynamic value of an event field is read by using its name as
-a C identifier.
+The dynamic value of an event field is read by using its name as a C
+identifier.
The dynamic value of a statically-known context field is read by
prefixing its name with `$ctx.`. Statically-known context fields are
context fields added to channels without the `$app.` prefix using the
-man:lttng-add-context(1) command.
+man:lttng-add-context(1) command. `$ctx.cpu_id` is also available as the
+ID of the CPU which emits the event.
The dynamic value of an application-specific context field is read by
prefixing its name with `$app.` (follows the format used to add such a