'''[http://www.tcl.tk/man/tcl/TclCmd/chan.htm%|%chan]''', a [Tcl Commands%|%built-in] Tcl command, manipulates [channel%|%channels].
** See Also **
[Additional file commands]: Tips and tricks for processing the content in a channel.
[chan mode]: an example of extening the `chan` ensemble
[stacked channel]:
[transform]:
`[ycl%|%ycl chan connect]`: Connect the output of one channel to the input of another. Uses a separate thread to avoid deadlocks.
`[ycl%|%ycl chan oschan]`: Creates a `[chan pipe]` facade around another channel, making it posible, for example to use a [reflected channel] with `<@`. Can also be used to work around the fact that `[exec]` (and therefore `[open]`) ignore encoding and translation in the case of `<@`.
** Synopsis **
: '''chan''' ''action'' ?''arg arg ...''?
** Documentation **
[http://www.tcl.tk/man/tcl/TclCmd/chan.htm%|%official reference]:
[TIP] [http://www.tcl.tk/cgi-bin/tct/tip/208%|%208]: add `chan`
** Description **
Introduced in [Tcl] [Changes in Tcl/Tk 8.5%|%8.5].
`chan` provides various operations on a channel, including many that have been
available using a mix of other commands. ''action'' indicates what to do with
the channel. Any unique abbreviation for an ''action'' is acceptable. The valid
''actions''s are:
*** New actions (no analog in rest of Tcl) ***
'''`[chan create]`''' ''mode cmdPrefix'': creates a channel using a ''cmdPrefix'' (e.g., an [namespace ensemble%|%ensemble] or [TclOO%|%object])
'''[chan pending]''' ''mode'' ''channelId'': returns the number of bytes (of input or output, depending on ''mode'') buffered internally
'''[chan pop]''' ''channelId'': pop one [transform] off a [stacked channel]
'''[chan postevent]''' ''channelId eventSpec'': generate event on channel (which it must be listening for)
'''[chan push]''' ''channelId'' ''cmdPrefix'': stack a [transform] on top of the ''channel''
'''[chan pipe]''': create a standalone pipe and return a pair of file descriptors for its read and write ends, in this order ([TIP] [http://tip.tcl.tk/304.html#304], available in Tcl >= 8.6).
'''[chan truncate]''' ''channelId'' ?''length''?: truncate the file behind the channel
----
[AMG]: `chan` aggregates all the commands you'll need for working with
channels, ''except'' creating traditional channels (it can only create pipes
and [reflected channel%|%reflected channels]). Use `[open]` or `[socket]` or an extension
command, same as always. If you find a core channel command not incorporated
as a `chan` subcommand, please report it.
*** Renamed actions (available as another command as well) ***
'''[chan blocked]''' ''channelId'': supercedes [fblocked]
'''[chan close]''' ''channelId'': supercedes [close]
'''[chan configure]''' ''channelId'' ?''optionName''? ?''value''? ?''optionName value''?...: supercedes [fconfigure]
'''[chan copy]''' ''inputChan outputChan'' ?''options...''?: same as [fcopy]
'''[chan eof]''' ''channelId'': supercedes [eof]
'''[chan event]''' ''channelId event'' ?''script''?: supercedes [fileevent]
'''[chan flush]''' ''channelId'': supercedes [flush]
'''[chan gets]''' ''channelId'' ?''varName''?: supercedes [gets]
'''[chan names]''' ?''globPattern''?: supercedes [file channels]
'''[chan puts]''' ?'''-nonewline'''? ?''channelId''? ''string'': supercedes [puts]
'''[chan read]''' ''channelId'' ?''numChars''?:
'''[chan read]''' ?'''-nonewline'''? ''channelId'': supercedes [read]
'''[chan seek]''' ''channelId offset'' ?''origin''?: supercedes [seek]
'''[chan tell]''' ''channelId'': supercedes [tell]
** History **
[RS]: History sometimes runs in circles... [Tcl 2.1] didn't have commands
dealing with channels. [Peter da Silva] added the "stream" extension, where one
could write
======
stream fp open $filename r
set x [stream fp gets]
stream fp close
======
Later, the parts of "stream" went into the core as separate commands. Still
later, in 8.5, they get reunited again in [chan], which arguably makes the
command set leaner, but scripts wordier...
<<categories>> Changes in Tcl/Tk 8.5 | Channel | Command