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Diffstat (limited to 'doc/read.n')
| -rw-r--r-- | doc/read.n | 87 |
1 files changed, 63 insertions, 24 deletions
@@ -5,10 +5,8 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: read.n,v 1.2 1998/09/14 18:39:54 stanton Exp $ -'\" +.TH read n 8.1 Tcl "Tcl Built-In Commands" .so man.macros -.TH read n 7.5 Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME @@ -16,35 +14,76 @@ read \- Read from a channel .SH SYNOPSIS \fBread \fR?\fB\-nonewline\fR? \fIchannelId\fR .sp -\fBread \fIchannelId numBytes\fR +\fBread \fIchannelId numChars\fR .BE - .SH DESCRIPTION .PP In the first form, the \fBread\fR command reads all of the data from -\fIchannelId\fR up to the end of the file. -If the \fB\-nonewline\fR switch is specified then the last character -of the file is discarded if it is a newline. -In the second form, the extra argument specifies how many bytes to -read. Exactly that many bytes will be read and returned, unless -there are fewer than \fInumBytes\fR left in the file; in this case -all the remaining bytes are returned. +\fIchannelId\fR up to the end of the file. If the \fB\-nonewline\fR +switch is specified then the last character of the file is discarded +if it is a newline. In the second form, the extra argument specifies +how many characters to read. Exactly that many characters will be +read and returned, unless there are fewer than \fInumChars\fR left in +the file; in this case all the remaining characters are returned. If +the channel is configured to use a multi-byte encoding, then the +number of characters read may not be the same as the number of bytes +read. +.PP +\fIChannelId\fR must be an identifier for an open channel such as the +Tcl standard input channel (\fBstdin\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. The channel must have +been opened for input. .PP -If \fIchannelId\fR is in nonblocking mode, the command may not read -as many bytes as requested: once all available input has been read, -the command will return the data that is available rather than blocking -for more input. -The \fB\-nonewline\fR switch is ignored if the command returns -before reaching the end of the file. +If \fIchannelId\fR is in nonblocking mode, the command may not read as +many characters as requested: once all available input has been read, +the command will return the data that is available rather than +blocking for more input. If the channel is configured to use a +multi-byte encoding, then there may actually be some bytes remaining +in the internal buffers that do not form a complete character. These +bytes will not be returned until a complete character is available or +end-of-file is reached. The \fB\-nonewline\fR switch is ignored if +the command returns before reaching the end of the file. .PP \fBRead\fR translates end-of-line sequences in the input into newline characters according to the \fB\-translation\fR option for the channel. -See the manual entry for \fBfconfigure\fR for details on the -\fB\-translation\fR option. - +See the \fBfconfigure\fR manual entry for a discussion on ways in +which \fBfconfigure\fR will alter input. +.SH "USE WITH SERIAL PORTS" +'\" Note: this advice actually applies to many versions of Tcl +.PP +For most applications a channel connected to a serial port should be +configured to be nonblocking: \fBfconfigure\fI channelId \fB\-blocking +\fI0\fR. Then \fBread\fR behaves much like described above. Care +must be taken when using \fBread\fR on blocking serial ports: +.TP +\fBread \fIchannelId numChars\fR +. +In this form \fBread\fR blocks until \fInumChars\fR have been received +from the serial port. +.TP +\fBread \fIchannelId\fR +. +In this form \fBread\fR blocks until the reception of the end-of-file +character, see \fBfconfigure\fR \fB\-eofchar\fR. If there no end-of-file +character has been configured for the channel, then \fBread\fR will +block forever. +.SH "EXAMPLE" +.PP +This example code reads a file all at once, and splits it into a list, +with each line in the file corresponding to an element in the list: +.PP +.CS +set fl [open /proc/meminfo] +set data [\fBread\fR $fl] +close $fl +set lines [split $data \en] +.CE .SH "SEE ALSO" -eof(n), fblocked(n), fconfigure(n) - +file(n), eof(n), fblocked(n), fconfigure(n), Tcl_StandardChannels(3) .SH KEYWORDS -blocking, channel, end of line, end of file, nonblocking, read, translation +blocking, channel, end of line, end of file, nonblocking, read, translation, encoding +'\"Local Variables: +'\"mode: nroff +'\"End: |