IO::BufferedSelect(3) User Contributed Perl Documentation IO::BufferedSelect(3)

IO::BufferedSelect - Line-buffered select interface

use IO::BufferedSelect;
my $bs = new BufferedSelect($fh1, $fh2);
while(1)
{
    my @ready = $bs->read_line();
    foreach(@ready)
    {
        my ($fh, $line) = @$_;
        my $fh_name = ($fh == $fh1 ? "fh1" : "fh2");
        print "$fh_name: $line";
    }
}

The "select" system call (and the "IO::Select" interface) allows us to process multiple streams simultaneously, blocking until one or more of them is ready for reading or writing. Unfortunately, this requires us to use "sysread" and "syswrite" rather than Perl's buffered I/O functions. In the case of reading, there are two issues with combining "select" with "readline": (1) "select" might block but the data we want is already in Perl's input buffer, ready to be slurped in by "readline"; and (2) "select" might indicate that data is available, but "readline" will block because there isn't a full $/-terminated line available.

The purpose of this module is to implement a buffered version of the "select" interface that operates on lines, rather than characters. Given a set of filehandles, it will block until a full line is available on one or more of them.

Note that this module is currently limited, in that (1) it only does "select" for readability, not writability or exceptions; and (2) it does not support arbitrary line separators ($/): lines must be delimited by newlines.

new ( HANDLES )
Create a "BufferedSelect" object for a set of filehandles. Note that because this class buffers input from these filehandles internally, you should only use the "BufferedSelect" object for reading from them (you shouldn't read from them directly or pass them to other BufferedSelect instances).

read_line
read_line ($timeout)
read_line ($timeout, @handles)
Block until a line is available on one of the filehandles. If $timeout is "undef", it blocks indefinitely; otherwise, it returns after at most $timeout seconds.

If @handles is specified, then only these filehandles will be considered; otherwise, it will use all filehandles passed to the constructor.

Returns a list of pairs "[$fh, $line]", where $fh is a filehandle and $line is the line that was read (including the newline, ala "readline"). If the filehandle reached EOF, then $line will be undef. Note that "reached EOF" is to be interpreted in the buffered sense: if a filehandle is at EOF but there are newline-terminated lines in "BufferedSelect"'s buffer, "read_line" will continue to return lines until the buffer is empty.

IO::Select

Antal Novak, <afn@cpan.org>

Copyright (C) 2007 by Antal Novak

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.

2021-05-24 perl v5.34.0