diff options
Diffstat (limited to 'doc/chan.n')
| -rw-r--r-- | doc/chan.n | 38 |
1 files changed, 26 insertions, 12 deletions
@@ -1,4 +1,4 @@ -'\" +'\" '\" Copyright (c) 2005-2006 Donal K. Fellows '\" '\" See the file "license.terms" for information on usage and redistribution @@ -200,7 +200,7 @@ generate an error. .TP \fB\-translation\fR \fImode\fR .TP -\fB\-translation\fR \fB{\fIinMode outMode\fB}\fR +\fB\-translation\fR \fB{\fIinMode outMode\fB}\fR . In Tcl scripts the end of a line is always represented using a single newline character (\en). However, in actual files and devices the end @@ -240,7 +240,7 @@ all platforms Tcl chooses \fBcrlf\fR, for all Unix flavors, it chooses \fBcrlf\fR. The default setting for \fB\-translation\fR is \fBauto\fR for both input and output. .TP -\fBbinary\fR +\fBbinary\fR . No end-of-line translations are performed. This is nearly identical to \fBlf\fR mode, except that in addition \fBbinary\fR mode also sets @@ -287,12 +287,14 @@ slow destinations like network sockets. .RS .PP The \fBchan copy\fR command transfers data from \fIinputChan\fR until -end of file or \fIsize\fR bytes have been transferred. If no -\fB\-size\fR argument is given, then the copy goes until end of file. -All the data read from \fIinputChan\fR is copied to \fIoutputChan\fR. -Without the \fB\-command\fR option, \fBchan copy\fR blocks until the -copy is complete and returns the number of bytes written to -\fIoutputChan\fR. +end of file or \fIsize\fR bytes or characters have been transferred; +\fIsize\fR is in bytes if the two channels are using the same encoding, +and is in characters otherwise. If no \fB\-size\fR argument is given, +then the copy goes until end of file. All the data read from +\fIinputChan\fR is copied to \fIoutputChan\fR. Without the +\fB\-command\fR option, \fBchan copy\fR blocks until the copy is +complete and returns the number of bytes or characters (using the same +rules as for the \fB\-size\fR option) written to \fIoutputChan\fR. .PP The \fB\-command\fR argument makes \fBchan copy\fR work in the background. In this case it returns immediately and the @@ -530,8 +532,8 @@ only those channel names that match it (according to the rules of . Depending on whether \fImode\fR is \fBinput\fR or \fBoutput\fR, returns the number of -bytes of input or output (respectively) currently buffered -internally for \fIchannelId\fR (especially useful in a readable event +bytes of input or output (respectively) currently buffered +internally for \fIchannelId\fR (especially useful in a readable event callback to impose application-specific limits on input line lengths to avoid a potential denial-of-service attack where a hostile user crafts an extremely long line that exceeds the available memory to buffer it). @@ -546,7 +548,19 @@ separately \fBstderr\fR and \fBstdout\fR from a subprocess. To do this, spawn with "2>@" or ">@" redirection operators onto the write side of a pipe, and then immediately close it in the parent. This is necessary to get an EOF on -the read side once the child has exited or otherwise closed its output. +the read side once the child has exited or otherwise closed its output. +.RS +.PP +Note that the pipe buffering semantics can vary at the operating system level +substantially; it is not safe to assume that a write performed on the output +side of the pipe will appear instantly to the input side. This is a +fundamental difference and Tcl cannot conceal it. The overall stream semantics +\fIare\fR compatible, so blocking reads and writes will not see most of the +differences, but the details of what exactly gets written when are not. This +is most likely to show up when using pipelines for testing; care should be +taken to ensure that deadlocks do not occur and that potential short reads are +allowed for. +.RE .VE 8.6 .TP \fBchan pop \fIchannelId\fR |