---
name: "observe"
section: "3tcl"
platform: "linux"
package: "tcllib"
version: "2.0+dfsg-4"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/observe"
---

# observe(3tcl)

Observer transformation, stream copy

```

```

## NAME

tcl::transform::observe - Observer transformation, stream copy

## SYNOPSIS

package require **Tcl 8.6 9**

package require **tcl::transform::core ?1.1?**

package require **tcl::transform::observe ?1.1?**

**::tcl::transform::observe** *chan* *logw* *logr*

```

```

## DESCRIPTION

The **tcl::transform::observer** package provides a command creating a channel transformation which passes the read and written bytes through unchanged (like **tcl::transform::identity**), but additionally copies the data it has seen for each direction into channels specified at construction time.

Related transformations in this module are **tcl::transform::adler32**, **tcl::transform::counter**, **tcl::transform::crc32**, and **tcl::transform::identity**.

The internal **TclOO** class implementing the transform handler is a sub-class of the **tcl::transform::core** framework.

## API

- **::tcl::transform::observe** *chan* *logw* *logr*

  This command creates an observer transformation on top of the channel *chan* and returns its handle. The channel handles *logr* and *logw* are there the data is copied to.

## BUGS, IDEAS, FEEDBACK

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category *virtchannel* of the *Tcllib Trackers* \[http://core.tcl.tk/tcllib/reportlist\]. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide *unified diffs*, i.e the output of **diff -u**.

Note further that *attachments* are strongly preferred over inlined patches. Attachments can be made by going to the **Edit** form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

## KEYWORDS

channel transformation, observer, reflected channel, stream copy, tip 230, transformation, virtual channel

## CATEGORY

Channels

## COPYRIGHT

```
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
```