docs/hop-user-manual/modules/ROOT/pages/pipeline/transforms/writetolog.adoc

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:documentationPath: /pipeline/transforms/
:language: en_US
:description: The Write To Log transform writes information to the Hop logging system.

= image:transforms/icons/writetolog.svg[Write to log transform Icon, role="image-doc-icon"] Write to log

[%noheader,cols="3a,1a", role="table-no-borders" ]
|===
|
== Description

The Write To Log transform writes information to the Hop logging system.

Typical use cases are logging specific values or custom logging messages to the Hop logs.

TIP: be careful when writing variables or fields for (unencrypted) passwords or other sensitive information to the Hop logging system!

|
== Supported Engines
[%noheader,cols="2,1a",frame=none, role="table-supported-engines"]
!===
!Hop Engine! image:check_mark.svg[Supported, 24]
!Spark! image:question_mark.svg[Maybe Supported, 24]
!Flink! image:question_mark.svg[Maybe Supported, 24]
!Dataflow! image:question_mark.svg[Maybe Supported, 24]
!===
|===

== Options

[options="header"]
|===
|Option|Description
|Transform Name|Name of the transform this name has to be unique in a single pipeline.
|Log level|The logging level to use.
|Print header|Whether or not the column names for data values is printed.
In the example below, this value has been set to false, so only the actual values (3, 4) are printed.
|Limit rows|Limit the number of rows given by the parameter "Nr. of rows to print".
|Nr. of rows to print|The number of rows to print when option "limit rows" is checked.
|Write to log|The text to use in the logging line(s).
|Fields|The data from fields that should we written to the log.
|===

== Example log output

[source,bash]
----
2020/05/14 12:30:52 - Write to log.0 -
2020/05/14 12:30:52 - Write to log.0 - ----------> Linenr 1----------------------------
2020/05/14 12:30:52 - Write to log.0 - test log
2020/05/14 12:30:52 - Write to log.0 -
2020/05/14 12:30:52 - Write to log.0 -  3
2020/05/14 12:30:52 - Write to log.0 -  4
2020/05/14 12:30:52 - Write to log.0 -
2020/05/14 12:30:52 - Write to log.0 - ====================
2020/05/14 12:30:52 - Write to log.0 -
2020/05/14 12:30:52 - Write to log.0 - ----------> Linenr 2----------------------------
2020/05/14 12:30:52 - Write to log.0 - test log
2020/05/14 12:30:52 - Write to log.0 -
2020/05/14 12:30:52 - Write to log.0 -  3
2020/05/14 12:30:52 - Write to log.0 -  4
2020/05/14 12:30:52 - Write to log.0 -
2020/05/14 12:30:52 - Write to log.0 - ====================
----