Provided by: tcl8.5-doc_8.5.19-4_all 
NAME
read - Read from a channel
SYNOPSIS
read ?-nonewline? channelId
read channelId numChars
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DESCRIPTION
In the first form, the read command reads all of the data from channelId up to the end of the file. If
the -nonewline 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 numChars 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.
ChannelId must be an identifier for an open channel such as the Tcl standard input channel (stdin), the
return value from an invocation of open or socket, or the result of a channel creation command provided
by a Tcl extension. The channel must have been opened for input.
If channelId 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 -nonewline switch is
ignored if the command returns before reaching the end of the file.
Read translates end-of-line sequences in the input into newline characters according to the -translation
option for the channel. See the fconfigure manual entry for a discussion on ways in which fconfigure
will alter input.
USE WITH SERIAL PORTS
For most applications a channel connected to a serial port should be configured to be nonblocking:
fconfigure channelId -blocking 0. Then read behaves much like described above. Care must be taken when
using read on blocking serial ports:
read channelId numChars
In this form read blocks until numChars have been received from the serial port.
read channelId
In this form read blocks until the reception of the end-of-file character, see fconfigure
-eofchar. If there no end-of-file character has been configured for the channel, then read will
block forever.
EXAMPLE
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:
set fl [open /proc/meminfo]
set data [read $fl]
close $fl
set lines [split $data \n]
SEE ALSO
file(3tcl), eof(3tcl), fblocked(3tcl), fconfigure(3tcl), Tcl_StandardChannels(3tcl)
KEYWORDS
blocking, channel, end of line, end of file, nonblocking, read, translation, encoding