diff options
Diffstat (limited to 'doc/seek.n')
| -rw-r--r-- | doc/seek.n | 17 |
1 files changed, 8 insertions, 9 deletions
@@ -14,17 +14,14 @@ seek \- Change the access position for an open channel .SH SYNOPSIS \fBseek \fIchannelId offset \fR?\fIorigin\fR? .BE - .SH DESCRIPTION .PP Changes the current access position for \fIchannelId\fR. .PP -.VS \fIChannelId\fR must be an identifier for an open channel such as a Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR), the return value from an invocation of \fBopen\fR or \fBsocket\fR, or the result of a channel creation command provided by a Tcl extension. -.VE .PP The \fIoffset\fR and \fIorigin\fR arguments specify the position at which the next read or write will occur @@ -32,20 +29,23 @@ for \fIchannelId\fR. \fIOffset\fR must be an integer (which may be negative) and \fIorigin\fR must be one of the following: .TP 10 \fBstart\fR +. The new access position will be \fIoffset\fR bytes from the start of the underlying file or device. .TP 10 \fBcurrent\fR +. The new access position will be \fIoffset\fR bytes from the current access position; a negative \fIoffset\fR moves the access position backwards in the underlying file or device. .TP 10 \fBend\fR +. The new access position will be \fIoffset\fR bytes from the end of the file or device. A negative \fIoffset\fR places the access position before the end of file, and a positive \fIoffset\fR places the access position after the end of file. -.LP +.PP The \fIorigin\fR argument defaults to \fBstart\fR. .PP The command flushes all buffered output for the channel before the command @@ -55,23 +55,24 @@ This command returns an empty string. An error occurs if this command is applied to channels whose underlying file or device does not support seeking. .PP -.VS 8.1 Note that \fIoffset\fR values are byte offsets, not character offsets. Both \fBseek\fR and \fBtell\fR operate in terms of bytes, not characters, unlike \fBread\fR. -.VE 8.1 .SH EXAMPLES +.PP Read a file twice: +.PP .CS set f [open file.txt] set data1 [read $f] \fBseek\fR $f 0 set data2 [read $f] close $f -# $data1 == $data2 if the file wasn't updated +# $data1 eq $data2 if the file wasn't updated .CE .PP Read the last 10 bytes from a file: +.PP .CS set f [open file.data] # This is guaranteed to work with binary data but @@ -81,9 +82,7 @@ fconfigure $f -translation binary set data [read $f 10] close $f .CE - .SH "SEE ALSO" file(n), open(n), close(n), gets(n), tell(n), Tcl_StandardChannels(3) - .SH KEYWORDS access position, file, seek |