Tcl8.5.16/Tk8.5.16 Documentation > TclCmd > gets

Tcl/Tk Applications | Tcl Commands | Tk Commands | Tcl Library | Tk Library

NAME

gets - Read a line from a channel

SYNOPSIS

gets channelId ?varName?

DESCRIPTION

This command reads the next line from channelId, returns everything in the line up to (but not including) the end-of-line character(s), and discards the end-of-line character(s).

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 varName is omitted the line is returned as the result of the command. If varName is specified then the line is placed in the variable by that name and the return value is a count of the number of characters returned.

If end of file occurs while scanning for an end of line, the command returns whatever input is available up to the end of file. If channelId is in nonblocking mode and there is not a full line of input available, the command returns an empty string and does not consume any input. If varName is specified and an empty string is returned in varName because of end-of-file or because of insufficient data in nonblocking mode, then the return count is -1. Note that if varName is not specified then the end-of-file and no-full-line-available cases can produce the same results as if there were an input line consisting only of the end-of-line character(s). The eof and fblocked commands can be used to distinguish these three cases.

EXAMPLE

This example reads a file one line at a time and prints it out with the current line number attached to the start of each line.

set chan [open "some.file.txt"]
set lineNumber 0
while {[gets $chan line] >= 0} {
    puts "[incr lineNumber]: $line"
}
close $chan

SEE ALSO

file, eof, fblocked, Tcl_StandardChannels

KEYWORDS

blocking, channel, end of file, end of line, line, nonblocking, read
Copyright © 1995-1997 Roger E. Critchlow Jr. Copyright © 1993 The Regents of the University of California. Copyright © 1994-1996 Sun Microsystems, Inc.