distrib/share/tcl/help/tcl/files/gets

   1 NAME
   2        gets - Read a line from a channel
   3
   4 SYNOPSIS
   5        gets channelId ?varName?
   6
   7
   8 DESCRIPTION
   9        This  command reads the next line from channelId, returns everything in
  10        the line up to (but not including) the  end-of-line  character(s),  and
  11        discards the end-of-line character(s).
  12
  13        ChannelId  must  be  an  identifier for an open channel such as the Tcl
  14        standard input channel (stdin), the return value from an invocation  of
  15        open or socket, or the result of a channel creation command provided by
  16        a Tcl extension. The channel must have been opened for input.
  17
  18        If varName is omitted the line is returned as the result  of  the  com-
  19        mand.   If varName is specified then the line is placed in the variable
  20        by that name and the return value is a count of the number  of  charac-
  21        ters returned.
  22
  23        If  end  of  file occurs while scanning for an end of line, the command
  24        returns whatever input is available up to the end of  file.   If  chan-
  25        nelId  is  in  nonblocking  mode  and there is not a full line of input
  26        available, the command returns an empty string and does not consume any
  27        input.  If varName is specified and an empty string is returned in var-
  28        Name because of end-of-file or because of  insufficient  data  in  non-
  29        blocking  mode,  then  the return count is -1.  Note that if varName is
  30        not specified then the end-of-file and no-full-line-available cases can
  31        produce the same results as if there were an input line consisting only
  32        of the end-of-line character(s).  The eof and fblocked commands can  be
  33        used to distinguish these three cases.
  34
  35 EXAMPLE
  36        This example reads a file one line at a time and prints it out with the
  37        current line number attached to the start of each line.
  38
  39               set chan [open "some.file.txt"]
  40               set lineNumber 0
  41               while {[gets $chan line] >= 0} {
  42                   puts "[incr lineNumber]: $line"
  43               }
  44               close $chan
  45
  46
  47 SEE ALSO
  48        file(n), eof(n), fblocked(n), Tcl_StandardChannels(3)
  49
  50
  51 KEYWORDS