Statements
The following elements can be used in statements.
Block
A block consists of one or more statements within curly braces ({}
).
This is typically used with conditional statements as in the example below.
If the expression matches, both log messages will be generated.
if now() > 2000-01-01 00:00:00
{
log_info("we are in the");
log_info("21st century");
}
Procedures
A procedure is a statement that performs a set of actions. Procedures can accept arguments. Unlike a function, a procedure modifies its arguments, the state of the NXLog Agent engine, the state of a module, or the current event. Procedures can be polymorphic, meaning that the same procedure can take different argument types.
Many NXLog language features are provided through procedures. See the list of available core procedures. Modules can provide additional procedures for use with the NXLog language.
This example uses the parse_syslog() procedure, provided by the xm_syslog module, to parse syslog records received via UDP.
<Input in>
Module im_udp
Host 0.0.0.0
Port 514
Exec parse_syslog();
</Input>
Procedures for a specific module instance can be called using the ->
operator. This statement calls the rotate_to()
procedure of an om_file instance named out
to rotate the current output
file.
out->rotate_to("output_logs");
Calling procedures of a specific instance is especially useful when the
configuration contains more than one instance of the same module. These
statements call the parse_xml() procedure of two
xm_xml instances, one named xml_a
and the other named xml_b
.
xml_a->parse_xml();
xml_b->parse_xml();
If-Else
A conditional statement starts with the if
keyword followed by a
boolean expression and a statement. The else
keyword, followed by
another statement, is optional. Brackets around the expression are
also optional.
A log message will be generated if the expression matches.
if now() > 2000-01-01 00:00:00 log_info("we are in the 21st century");
This statement is the same as the previous one but uses brackets.
if ( now() > 2000-01-01 00:00:00 ) log_info("we are in the 21st century");
This is a conditional statement block.
if now() > 2000-01-01 00:00:00
{
log_info("we are in the 21st century");
}
This conditional statement block includes an else branch.
if now() > 2000-01-01 00:00:00
{
log_info("we are in the 21st century");
}
else log_info("we are not yet in the 21st century");
Like Perl, the NXLog language does not have a switch statement. Instead, this can be accomplished by using conditional if-else statements.
The generated log message varies based on the value of the $value
field.
if ( $value == 1 )
log_info("1");
else if ( $value == 2 )
log_info("2");
else if ( $value == 3 )
log_info("3");
else
log_info("default");
The Perl elsif and unless keywords are not supported. |
While
A basic looping construct in NXLog language. The syntax is:
while ( cond_expression ) { statement; statement; ... statement; }
Where cond_expression
is any valid NXLog language
expression which evaluates to a boolean value.
The statements
will be executed repeatedly as long
as the cond_expression
evaluates to TRUE.
It is important to note that currently nothing prevents infinite loops therefore it is the responsibility of the user to not create such loops. |
An example:
$$i = 0; while ( $$i < 5 ) { log_info("Repeated message"); $$i = $$i + 1; }
while
loops can be nested without limitations but
the best practice is to limit the nesting level in
order to avoid long-running exec blocks.
Foreach
A looping construct in NXLog language designed to work on containers. The syntax is:
foreach (expression, module-variable) { statement; statement; ... statement; }
Where expression
is any valid NXLog language
expression which evaluates to a container type of
value like array
or hash
. But if one wants to
change the values in that container
then the expression
must "address" a container or
a sub-container already assigned to a field or to
a module variable. Any temporary container, which can
be a container literal or a function’s return value,
will be disposed outside the loop.
The module-variable
is a $$
notation for a
module variable.
The statements
will be executed as many times
as many elements the container has (expression
) and
for each repetition, the module-variable
will be updated
with the access key for a container element. In case of
arrays the module-variable
will hold the index values,
while in the case of hash containers, this will hold the
keys for the stored values.
An example:
$$array = [1, 2, 3]; foreach ($$array, $$idx) { $$array[$$idx] = $$array[$$idx] * 10; } $$hash = ( '1' => 100, '2' => 500); foreach($$hash, $$key) { $$hash[$$key] = $$hash[$$key] - 5; }
foreach
loops can be nested without limitations but
the best practice is to limit the nesting level in
order to avoid long-running exec blocks.
Break, Continue
Like programming or scripting languages NXLog Agent loops
also have these statements and the effects are the same.
In loop body break;
causes immediate leaving of
the loop while continue;
causes skipping the
rest of the statements after the continue;
.
In the case of nested loops, these statements affect the
loop in which the break
or the continue
resides.
E.g.:
$ar = [9,8,7,6,5,4,3,2,1]; foreach($ar, $$i) { if ( $ar[$$i] == 4 ) { continue; } if ( $ar[$$i] == 2 ) { break; } if ( $ar[$$i] % 2 == 0 ) $ar[$$i] = "xxx"; }