chan - Manipulate channels

http://purl.org/tcl/home/man/tcl8.5/TclCmd/chan.htm 

'''chan''' ''option'' ?''arg arg ...''?
** See Also **
This command (introduced in Tcl 8.5) provides several operations on a channel, including many that have been available using a mix of other commands. ''Option'' indicates what to do with the channel. Any unique abbreviation for ''option'' is acceptable. The valid ''option''s are: (see the man page listed above for more details; on this web page, notes on selected options have been contributed).
    :   '''chan''' ''action'' ?''arg arg ...''?
''Why was this thing called 'chan' instead of 'channel'?'' 
[schlenk]: It's mentioned in the TIP [http://www.tcl.tk/cgi-bin/tct/tip/208.html], basically the same naming style as [interp] for interpreter. 
    [TIP] [http://www.tcl.tk/cgi-bin/tct/tip/208%|%208]:   add `chan`
''I see. Thank
you for pointing that out. Pretty lame reasoning when "channel" is much more descriptive. But I'm not the 
one doing all the work so I'm not complaining! ''

[JYL] If you dont like chan you can do 'interp alias {} channel {} chan'


[AMG]: `chan` aggregates all the commands you'll need for working with
'''[chan blocked]''' ''channelId'' - like [fblocked]

'''[chan close]''' ''channelId'' - like [close]

'''[chan configure]''' ''channelId'' ?''optionName''? ?''value''? ?''optionName value''?... - like [fconfigure]

'''[chan copy]''' ''inputChan outputChan'' ?''options...''?

'''[chan create]''' ''mode cmdPrefix''

'''[chan eof]''' ''channelId'' - like [eof]

'''[chan event]''' ''channelId event'' ?''script''? - like [fileevent]

'''[chan flush]''' ''channelId'' - like [flush]

'''[chan gets]''' ''channelId'' ?''varName''? - like [gets]

'''[chan names]''' ?''globPattern''? - like [file channels]

'''[chan pending]''' ''mode'' ''channelId'' - returns the number of bytes (of input or output, depending on ''mode'') buffered internally

'''[chan postevent]''' ''channelId eventSpec''

'''[chan pipe]''' - create a standalone pipe and return a pair of file descriptors for its read and write ends, in this order ([TIP] #304 [http://tip.tcl.tk/304.html], available in Tcl >= 8.6).

'''[chan puts]''' ?'''-nonewline'''? ?''channelId''? ''string'' - like [puts]

'''[chan read]''' ''channelId'' ?''numChars''? - like [read]

'''[chan read]''' ?'''-nonewline'''? ''channelId'' -like [read]

'''[chan seek]''' ''channelId offset'' ?''origin''? - like [seek]

'''[chan tell]''' ''channelId'' - like [tell]

'''[chan truncate]''' ''channelId'' ?''length''?

----

TIP 287 proposes a [['''chan available''' ''channelId'']] command to find out how much available input is currently being buffered that could be [chan read] in. (It would make it safe to use [chan gets] with [socket]s since you could introspect and detect someone sending an excessively long line rather than running out of memory first.)

See also [chan mode] for an example how to extend that [ensemble].
----
[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...
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[MG] has just needed to find out how long the eol sequence in a particular file was. Checking fconfigure $fid -translation didn't help (as it was just 'auto' on the read, and always crlf (Win XP) on the write, even if the file used Unix line-endings). Came up with this (which is possibly obvious, but I'm rather pleased with myself anyway;)
======
proc lineEndingSize {file} {
    set fid [open $file r]
    chan gets $fid line
    set size [expr { [chan tell $fid] - [string bytelength $line] }]
    close $fid
    return $size;
}
======

[DKF]: That can go wrong. The problem is that you need to use the encoded length of the string read, and some encodings have multiple ways of encoding a particular character. This is all rather nasty; even guessing based on the value of '''[fconfigure] -encoding''' can go wrong! So instead try this:
======
proc lineEndingSize file {
   set f [open $file]
   gets $f line
   set after [tell $f]
   seek $f 0
   read $f [string length $line]
   set before [tell $f]
   close $f
   return [expr {$after - $before}]
}
======

[MG] I'll try that instead, thanks :)
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!!!!!!
%|[Category Command] of [Tcl] 8.5 |[Category Channel]|%
!!!!!!