Directives

The Zeek scripting language supports a number of directives that can affect which scripts will be loaded or which lines in a script will be executed. Directives are evaluated before script execution begins.

@DIR

Expands to the directory pathname where the current script is located.

Example:

print "Directory:", @DIR;

@FILENAME

Expands to the filename of the current script.

Example:

print "File:", @FILENAME;

@deprecated

Marks the current script as deprecated. This can be placed anywhere in the script, but a good convention is to put it as the first line. You can also supply additional comments.

Example:

@deprecated "Use '@load foo' instead"

@load

Loads the specified Zeek script, specified as the relative pathname of the file (relative to one of the directories in Zeek’s file search path). If the Zeek script filename ends with .zeek, then you don’t need to specify the file extension. The filename cannot contain any whitespace.

In this example, Zeek will try to load a script policy/misc/capture-loss.zeek by looking in each directory in the file search path (the file search path can be changed by setting the ZEEKPATH environment variable):

@load policy/misc/capture-loss

If you specify the name of a directory instead of a filename, then Zeek will try to load a file in that directory called __load__.zeek (presumably that file will contain additional @load directives).

In this example, Zeek will try to load a file tuning/defaults/__load__.zeek by looking in each directory in the file search path:

@load tuning/defaults

The purpose of this directive is to ensure that all script dependencies are satisfied, and to avoid having to list every needed Zeek script on the command-line. Zeek keeps track of which scripts have been loaded, so it is not an error to load a script more than once (once a script has been loaded, any subsequent load directives for that script are ignored).

@load-plugin

Activate a dynamic plugin with the specified plugin name. The specified plugin must be located in Zeek’s plugin search path. Example:

@load-plugin Demo::Rot13

By default, Zeek will automatically activate all dynamic plugins found in the plugin search path (the search path can be changed by setting the environment variable ZEEK_PLUGIN_PATH to a colon-separated list of directories). However, in bare mode (zeek -b dynamic plugins can be activated only by using load-plugin or by specifying the full plugin name on the Zeek command-line (e.g., zeek Demo::Rot13 or by setting the environment variable ZEEK_PLUGIN_ACTIVATE to a comma-separated list of plugin names.

@load-sigs

This works similarly to load except that in this case the filename represents a signature file (not a Zeek script). If the signature filename ends with sig then you don’t need to specify the file extension in the load-sigs directive. The filename cannot contain any whitespace.

In this example, Zeek will try to load a signature file base/protocols/ssl/dpd.sig

@load-sigs base/protocols/ssl/dpd

The format for a signature file is explained in the documentation for the Signature Framework.

@unload

This specifies a Zeek script that we don’t want to load (so a subsequent attempt to load the specified script will be skipped). However, if the specified script has already been loaded, then this directive has no affect.

In the following example, if the policy/misc/capture-loss.zeek script has not been loaded yet, then Zeek will not load it:

@unload policy/misc/capture-loss

@prefixes

Specifies a filename prefix to use when looking for script files to load automatically. The prefix cannot contain any whitespace.

In the following example, the prefix cluster is used and all prefixes that were previously specified are not used:

@prefixes = cluster

In the following example, the prefix cluster-manager is used in addition to any previously-specified prefixes:

@prefixes += cluster-manager

The way this works is that after Zeek parses all script files, then for each loaded script Zeek will take the absolute path of the script and then it removes the portion of the directory path that is in Zeek’s file search path. Then it replaces each / character with a period . and then prepends the prefix (specified in the @prefixes directive) followed by a period. The resulting filename is searched for in each directory in Zeek’s file search path. If a matching file is found, then the file is automatically loaded.

For example, if a script called local.zeek has been loaded, and a prefix of test was specified, then Zeek will look for a file named test.local.zeek in each directory of Zeek’s file search path.

An alternative way to specify prefixes is to use the -p Zeek command-line option.

@if

The specified expression must evaluate to type bool. If the value is true, then the following script lines (up to the next @else or @endif) are available to be executed.

Example:

@if ( ver == 2 )
    print "version 2 detected";
@endif

@ifdef

This works like @if, except that the result is true if the specified identifier is defined.

Example:

@ifdef ( pi )
    print "pi is defined";
@endif

@ifndef

This works exactly like @ifdef, except that the result is true if the specified identifier is not defined.

Example:

@ifndef ( pi )
    print "pi is not defined";
@endif

@else

This directive is optional after an @if, @ifdef, or @ifndef. If present, it provides an else clause.

Example:

@ifdef ( pi )
    print "pi is defined";
@else
    print "pi is not defined";
@endif

@endif

This directive is required to terminate each @if, @ifdef, or @ifndef.

@DEBUG

TODO