---
name: "IO::BufferedSelect"
section: "3pm"
platform: "linux"
package: "libio-bufferedselect-perl"
version: "1.0-3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/IO::BufferedSelect"
---

# IO::BufferedSelect(3pm)

Line-buffered select interface

## NAME

IO::BufferedSelect - Line-buffered select interface

## SYNOPSIS

```
    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";
        }
    }
```

## DESCRIPTION

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.

## CONSTRUCTOR

- 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).

## METHODS

- 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.

## SEE ALSO

IO::Select

## AUTHOR

Antal Novak, \<afn@cpan.org\>

## COPYRIGHT AND LICENSE

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.