---
name: "close"
section: "n"
platform: "macos"
package: "tcl"
version: "152"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/close/n"
---

# close(n)

Close an open channel

## NAME

close - Close an open channel

## SYNOPSIS

**close** *channelId*

## DESCRIPTION

Closes the channel given by *channelId*.

*ChannelId* must be an identifier for an open channel such as a Tcl standard channel (**stdin**, **stdout**, or **stderr**), the return value from an invocation of **open** or **socket**, or the result of a channel creation command provided by a Tcl extension.

All buffered output is flushed to the channel's output device, any buffered input is discarded, the underlying file or device is closed, and *channelId* becomes unavailable for use.

If the channel is blocking, the command does not return until all output is flushed. If the channel is nonblocking and there is unflushed output, the channel remains open and the command returns immediately; output will be flushed in the background and the channel will be closed when all the flushing is complete.

If *channelId* is a blocking channel for a command pipeline then **close** waits for the child processes to complete.

If the channel is shared between interpreters, then **close** makes *channelId* unavailable in the invoking interpreter but has no other effect until all of the sharing interpreters have closed the channel. When the last interpreter in which the channel is registered invokes **close**, the cleanup actions described above occur. See the **interp** command for a description of channel sharing.

Channels are automatically closed when an interpreter is destroyed and when the process exits.  Channels are switched to blocking mode, to ensure that all output is correctly flushed before the process exits.

The command returns an empty string, and may generate an error if an error occurs while flushing output.  If a command in a command pipeline created with **open** returns an error, **close** generates an error (similar to the **exec** command.)

## EXAMPLE

This illustrates how you can use Tcl to ensure that files get closed even when errors happen by combining **catch**, **close** and **return**: proc withOpenFile {filename channelVar script} {\
     upvar 1 $channelVar chan\
     set chan \[open $filename\]\
     catch {\
         uplevel 1 $script\
     } result options\
     **close** $chan\
     return -options $options $result }

## SEE ALSO

[file(n)](/file/n.md), [open(n)](/open/n.md), [socket(n)](/socket/n.md), [eof(n)](/eof/n.md), [Tcl\_StandardChannels(3)](/Tcl_StandardChannels/3.md)

## KEYWORDS

blocking, channel, close, nonblocking