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.

Example Configuration

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

<match pattern>
  @type exec
  command cmd arg arg
  <format>
    @type tsv
    keys k1,k2,k3
  </format>
  <inject>
    tag_key k1
    time_key k2
    time_format %Y-%m-%d %H:%M:%S
  </inject>
</match>

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 fizzbuzz.py 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:
        output.write(s+"\n")
    else:
        output.write(str(fizzbuzz)+"\n")
output.close

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

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

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/fizzbuzz.py /path/to/buffer_path is run. This is why in fizzbuzz.py, 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
1
2
fizz
4
buzz
fizz
7
8
fizz
buzz
11
fizz
13
14
fizzbuzz

Supported modes

• Asynchronous

See Output Plugin Overview for more details.

Plugin helpers

• ​inject​

• ​formatter​

• ​compat_parameters​

• ​child_process​

Parameters

​Common Parameters​

@type

The value must be exec.

command

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\".

command_timeout

Command (program) execution timeout.

<format> section

See Format section configurations for more details.

@type

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.

time_type

Overwrite default value in this plugin.

localtime

Overwrite default value in this plugin.

<buffer> section

See Buffer section configurations for more details.

delayed_commit_timeout

Overwrite default value in this plugin.

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.