eof - Check for end of file condition on [channel]

    :   '''eof''' ''channelId''

Returns '''1''' if an end of file condition occurred during the most recent input operation on ''channelId'' (such as '''[gets]'''), '''0''' otherwise.

''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. 

<<discussion>>

'''eof''' is, in one sense, a command:

http://purl.org/tcl/home/man/tcl8.4/TclCmd/eof.htm

and, in another sense, an acronym for ''End Of File''.

----

Programmers can use eof to determine whether the channel has reached the end of input.

Note that it fires only after the last successful [gets] or [read], so testing for a -1 return value on [gets] may be a better idea, and avoid eof's [FMM] [http://phaseit.net/claird/comp.lang.tcl/fmm.html#eof] by coding:
======
 while {[gets $fp line]>=0} {...}
======
instead of
======
 while {![eof $fp]} {
    gets $fp line
    if [eof $fp] break ;# otherwise loops one time too many
    ...
 } ;# RS  
======

[DKF]: There are other conditions under which a non-blocking channel can cause a -1 to be returned by [gets], notably as determined by [fblocked].
----

The eof condition is only updated by a read, so the read loop with one conditional is:
======
 gets $fp line
 while {![eof $fp]} {
     # process line
     gets $fp line
 }
======

/Str.
----

Hmmm... the only thing I find eof good for is as a condition which should trigger closing a socket.

That is, if you are trying to read a non-blocking socket and you hit eof, you KNOW that it's time to close the socket.

'''-PSE'''

----

Can anyone indicate whether there are certain types of channels (pipe, socket, etc.) where eof doesn't do what one might at first blush expect?

[JMN] 2003-07-15 This isn't directly referring to the eof command - but is an EOF issue that I wasn't expecting so here looks as good a place as any to mention it.

Using the [Memchan] package, I was trying to [fcopy] from a memchan to a file roughly like so:

======
 package require Tcl
 package require Memchan

 set fd [open "/tmp/output.txt" "w"]
 set m [memchan]
 puts $m "someStringData"
 seek $m 0 start
 fcopy $m $fd -command CopyFinished
 
 proc CopyFinished args { puts $args }

 puts "Application has completed"
======

This performed the copy to file just fine, but the CopyFinished proc never got called. To fix this, I called 

======
 fconfigure $m -eofchar {}
======

before the puts someStringData line and

======
 fconfigure $m -eofchar \x1a
======

before the fcopy line. Then I changed the puts line to:

======
 puts $m "someStringData\x1a"
======

This seems like a bit of hoop-jumping to get the expected fcopy behaviour.. am I missing something simple?

<<discussion>>

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