like the OS call, returns the value of the environment variable, if it exists. Returns an empty string if it does not exist.

The following example can be used to build a dynamic filter based on some environment variable:

if $msg contains getenv('TRIGGERVAR') then /path/to/errfile


returns the length of the provided string


converts the provided string into lowercase


converts expr to a string value


converts expr to a number (integer) Note: if the expression does not contain a numerical value, behaviour is undefined.

wrap(str, wrapper_str)

returns the str wrapped with wrapper_str. Eg.
wrap("foo bar", "##")


"##foo bar##"

wrap(str, wrapper_str, escaper_str)

returns the str wrapped with wrapper_str. But additionally, any instances of wrapper_str appearing in str would be replaced by the escaper_str. Eg.
wrap("foo'bar", "'", "_")



replace(str, substr_to_replace, replace_with)

returns new string with all instances of substr_to_replace replaced by replace_with. Eg.
replace("foo bar baz", " b", ", B")


"foo, Bar, Baz".

re_match(expr, re)

returns 1, if expr matches re, 0 otherwise. Uses POSIX ERE.

re_extract(expr, re, match, submatch, no-found)

extracts data from a string (property) via a regular expression match. POSIX ERE regular expressions are used. The variable “match” contains the number of the match to use. This permits to pick up more than the first expression match. Submatch is the submatch to match (max 50 supported). The “no-found” parameter specifies which string is to be returned in case when the regular expression is not found. Note that match and submatch start with zero. It currently is not possible to extract more than one submatch with a single call.

field(str, delim, matchnbr)

returns a field-based substring. str is the string to search, delim is the delimiter and matchnbr is the match to search for (the first match starts at 1). This works similar as the field based property-replacer option. Versions prior to 7.3.7 only support a single character as delimiter character. Starting with version 7.3.7, a full string can be used as delimiter. If a single character is being used as delimiter, delim is the numerical ascii value of the field delimiter character (so that non-printable characters can by specified). If a string is used as delimiter, a multi-character string (e.g. “#011”) is to be specified.

Note that when a single character is specified as string field($msg, ",", 3) a string-based extraction is done, which is more performance intensive than the equivalent single-character field($msg, 44 ,3) extraction. Eg.

set $!usr!field = field($msg, 32, 3);  -- the third field, delimited by space

set $!usr!field = field($msg, "#011", 2); -- the second field, delimited by "#011"


Sets a variable through the execution of a template. Basically this permits to easily extract some part of a property and use it later as any other variable.
template(name="extract" type="string" string="%msg:F:5%")
set $!xyz = exec_template("extract");

the variable xyz can now be used to apply some filtering :

if $!xyz contains 'abc' then {action()}

or to build dynamically a file path :

template(name="DynaFile" type="string" string="/var/log/%$!xyz%-data/%timereported%-%$!xyz%.log")

Read more about it here :


mimics a traditional PRI-based filter (like “*.*” or “”). The traditional filter string must be given as a constant string. Dynamic string evaluation is not permitted (for performance reasons).

dyn_inc(bucket_name_literal_string, str)

Increments counter identified by str in dyn-stats bucket identified by bucket_name_literal_string. Returns 0 when increment is successful, any other return value indicates increment failed.

Counters updated here are reported by impstats.

Except for special circumstances (such as memory allocation failing etc), increment may fail due to metric-name cardinality being under-estimated. Bucket is configured to support a maximum cardinality (to prevent abuse) and it rejects increment-operation if it encounters a new(previously unseen) metric-name(str) when full.

Read more about it here Dynamic Stats

lookup(table_name_literal_string, key)

Lookup tables are a powerful construct to obtain class information based on message content. It works on top of a data-file which maps key (to be looked up) to value (the result of lookup).

The idea is to use a message properties (or derivatives of it) as an index into a table which then returns another value. For example, $fromhost-ip could be used as an index, with the table value representing the type of server or the department or remote office it is located in.

Read more about it here Lookup Tables


Converts an integer into an IPv4-address and returns the address as string. Input is an integer with a value between 0 and 4294967295. The output format is ‘>decimal<.>decimal<.>decimal<.>decimal<’ and ‘-1’ if the integer input is invalid or if the function encounters a problem.


Converts an IPv4-address into an integer and returns the integer. Input is a string; the expected address format may include spaces in the beginning and end, but must not contain any other characters in between (except dots). If the format does include these, the function results in an error and returns -1.


Generates a random number between 0 and the number specified, though the maximum value supported is platform specific.

  • If a number is not specified then 0 is returned.
  • If 0 is provided as the maximum value, then 0 is returned.
  • If the specified value is greater than the maximum supported for the current platform, then rsyslog will log this in the debug output and use the maximum value supported instead.

While the original intent of this function was for load balancing, it is generic enough to be used for other purposes as well.


The random number must not be assumed to be crypto-grade.

New in version 8.12.0.


Removes any spaces at the start of a given string. Input is a string, output is the same string starting with the first non-space character.


Removes any spaces at the end of a given string. Input is a string, output is the same string ending with the last non-space character.

substring(str, start, subStringLength)

Creates a substring from str. The substring begins at start and is at most subStringLength characters long.


returns a hexadecimal number string of a given positive integer num.


Returns the error state of functions that support it. C-Developers note that this is similar to errno under Linux. The error state corresponds to the function immediatly called before. The next function call overrides it.

Right now, the value 0 means that that the previous functions succeeded, any other value that it failed. In the future, we may have more fine-grain error codes.

Function descriptions mention if a function supports error state information. If not, the function call will always set script_error() to 0.


This boolenan function returns 1 (true) if the previous action is suspended, 0 (false) otherwise. It can be used to initiate action that shall happen if a function failed. Please note that an action failure may not be immediately detected, so the function return value is a bit fuzzy. It is guaranteed, however that a suspension will be detected with the next batch of messages that is being processed.


If, for example, you want to execute a rule set in case of failure of an action, do this:

ruleset(name="output_writer") {
    action(type="omfile" file="rsyslog.log")

action(type="omfwd" protocol="tcp" target="")
if previous_action_suspended() then
       call output_writer

format_time(unix_timestamp, format_str)

NOTE: this is EXPERIMENTAL code – it may be removed or altered in later versions than 8.30.0. Please watch the ChangeLog closely for updates.

Converts a UNIX timestamp to a formatted RFC 3164 or RFC 3339 date/time string. The first parameter is expected to be an integer value representing the number of seconds since 1970-01-01T00:00:0Z (UNIX epoch). The second parameter can be one of "date-rfc3164" or "date-rfc3339". The output is a string containing the formatted date/time. Date/time strings are expressed in UTC (no time zone conversion is provided).

  • Note: If the input to the function is NOT a proper UNIX timestamp, a string containing the original value of the parameter will be returned instead of a formatted date/time string.
format_time(1507165811, "date-rfc3164")


Oct  5 01:10:11


format_time(1507165811, "date-rfc3339")



In the case of an invalid UNIX timestamp:

format_time("foo", "date-rfc3339")

it produces the original value:


parse_json(string, container)

Parses the json string string and places the resulting json object into container where container can be any valid rsyslog variable. Returns 0 on success and something otherwise if string does not contain valid json.


Converts an RFC 3164 or RFC 3339 formatted date/time string to a UNIX timestamp (an integer value representing the number of seconds since the UNIX epoch: 1970-01-01T00:00:0Z).

If the input to the function is not a properly formatted RFC 3164 or RFC 3339 date/time string, or cannot be parsed, 0 is returned and script_error() will be set to error state.

  • Note: This function does not support unusual RFC 3164 dates/times that contain year or time zone information.
  • Note: Fractional seconds (if present) in RFC 3339 date/time strings will be discarded.
parse_time("Oct  5 01:10:11") # Assumes the current year (2017, in this example)







is_time(timestamp, format_str)

Checks the given timestamp to see if it is a valid date/time string (RFC 3164, or RFC 3339), or a UNIX timestamp.

This function returns 1 for valid date/time strings and UNIX timestamps, 0 otherwise. Additionally, if the input cannot be parsed, or there is an error, script_error() will be set to error state.

The format_str parameter is optional, and can be one of "date-rfc3164""date-rfc3339" or "date-unix". If this parameter is specified, the function will only succeed if the input matches that format. If omitted, the function will compare the input to all of the known formats (indicated above) to see if one of them matches.

  • Note: This function does not support unusual RFC 3164 dates/times that contain year or time zone information.
is_time("Oct  5 01:10:11")

all produce



is_time("2017-10-05T01:10:11+04:00", "date-rfc3339")




is_time("2017-10-05T01:10:11+04:00", "date-unix")



See also

If you would like to contribute to these docs, but are unsure where to start, please see the rsyslog-doc project README for an overview of the process. If you would like to contribute to the main source project, please review the contribution guidelines listed in the rsyslog project README.

If you have a question about these docs or Rsyslog in general, please see the following resources:


邮箱地址不会被公开。 必填项已用*标注