Versions | v1.0 (td-agent3) | v0.12 (td-agent2)

exec Output Plugin

The out_exec TimeSliced Output plugin passes events to an external program. The program receives the path to a file containing the incoming events as its last argument. The file format is tab-separated values (TSV) by default.

Table of Contents

Example Configuration

out_exec is included in Fluentd’s core. No additional installation process is required.

<match pattern>
  @type exec
  command cmd arg arg
    @type tsv
    keys k1,k2,k3
    tag_key k1
    time_key k2
    time_format %Y-%m-%d %H:%M:%S
Please see the Config File article for the basic structure and syntax of the configuration file.

Example: Running FizzBuzz against data stream

This example illustrates how to run FizzBuzz with out_exec.

We assume that the input file is specified by the last argument in the command line (“ARGV[-1]”). The following script runs FizzBuzz against the new-line delimited sequence of natural numbers (1, 2, 3…) and writes the output to “foobar.out”.

#!/usr/bin/env python
import sys
input = file(sys.argv[-1])
output = file("foobar.out", "a")
for line in input:
    fizzbuzz = int(line.split("\t")[0])
    s = ''
    if fizzbuzz%3 == 0:
        s += 'fizz'
    if fizzbuzz%5 == 0:
        s += 'buzz'
    if len(s) > 0:

Note that this program is written in Python. For out_exec (as well as out_exec_filter and in_exec), the program can be written in any language, not just Ruby.

Then, configure Fluentd as follows

  @type forward
<match fizzbuzz>
  @type exec
  command python /path/to/
    @type file
    path /path/to/buffer_path
    flush_interval 5s # for debugging/checking
    @type tsv
    keys fizzbuzz

The “@type tsv” and “keys fizzbuzz” in <format> tells Fluentd to extract the “fizzbuzz” field and output it as TSV. This simple example has a single key, but you can of course extract multiple fields and use “format json” to output newline-delimited JSONs.

The intermediary TSV is at /path/to/buffer_path, and the command python /path/to/ /path/to/buffer_path is run. This is why in, it’s reading the file at sys.argv[-1].

If you start Fluentd and run

$ for i in `seq 15`; do echo "{\"fizzbuzz\":$i}" | fluent-cat fizzbuzz; done

Then, after 5 seconds, you get a file named foobar.out.

$ cat foobar.out

Supported modes

  • Asynchronous

See Output Plugin Overview for more details.

Plugin helpers


Common Parameters


The value must be exec.


type default version
string Nothing 0.14.0

The command (program) to execute. The exec plugin passes the path of flushed buffer chunk as the last argument.

If you set command parameter like below:

command cmd arg arg

actual command execution is:

cmd arg arg /path/to/file
If "cmd" doesn't exist in PATH, you need to specify absolute path, e.g. "/path/to/cmd".


type default version
time 270 0.14.9

Command (program) execution timeout.

<format> section

See Format section configurations for more details.


type default version
string tsv 0.14.9

The format used to map the incoming events to the program input.

Overwrite default value in this plugin.

<inject> section

See Inject section configurations for more details.


type default version
string string 0.14.9

Overwrite default value in this plugin.


type default version
bool false 0.14.9

Overwrite default value in this plugin.

<buffer> section

See Buffer section configurations for more details.


type default version
time 300 0.14.9

Overwrite default value in this plugin.

Last updated: 2018-05-23 05:05:19 +0000

Versions | v1.0 (td-agent3) | v0.12 (td-agent2)

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.