'\" '\" Copyright (c) 1993 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) read.n,v 1.5 2003/01/21 19:40:00 hunt Exp '\" .so man.macros .TH read n 8.1 Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME read \- Read from a channel .SH SYNOPSIS \fBread \fR?\fB\-nonewline\fR? \fIchannelId\fR .sp \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 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 .VS \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. .VE .PP 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 \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 For most applications a channel connected to a serial port should be configured to be nonblocking: \fBfconfigure \fIchannelId \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 -eofchar\fR. If there no end-of-file character has been configured for the channel, then \fBread\fR will block forever. .SH "SEE ALSO" file(n), eof(n), fblocked(n), fconfigure(n), Tcl_StandardChannels(3) .SH KEYWORDS blocking, channel, end of line, end of file, nonblocking, read, translation, encoding