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Manual Reference Pages  -  TEST::BUILDER::IO::SCALAR (3)

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Test::Builder::IO::Scalar - A copy of IO::Scalar for Test::Builder



This is a copy of IO::Scalar which ships with Test::Builder to support scalar references as filehandles on Perl 5.6. Newer versions of Perl simply use open()’s built in support.

Test::Builder can not have dependencies on other modules without careful consideration, so its simply been copied into the distribution.


This file came from the IO-stringy Perl5 toolkit.

Copyright (c) 1996 by Eryq. All rights reserved. Copyright (c) 1999,2001 by ZeeGee Software Inc. All rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


new [ARGS...] Class method. Return a new, unattached scalar handle. If any arguments are given, they’re sent to open().
open [SCALARREF] Instance method. Open the scalar handle on a new scalar, pointed to by SCALARREF. If no SCALARREF is given, a private scalar is created to hold the file data.

Returns the self object on success, undefined on error.

opened Instance method. Is the scalar handle opened on something?
close Instance method. Disassociate the scalar handle from its underlying scalar. Done automatically on destroy.

    Input and output

flush Instance method. No-op, provided for OO compatibility.
getc Instance method. Return the next character, or undef if none remain.
getline Instance method. Return the next line, or undef on end of string. Can safely be called in an array context. Currently, lines are delimited by \n.
getlines Instance method. Get all remaining lines. It will croak() if accidentally called in a scalar context.
print ARGS... Instance method. Print ARGS to the underlying scalar.

<B>Warning:B> this continues to always cause a seek to the end of the string, but if you perform seek()s and tell()s, it is still safer to explicitly seek-to-end before subsequent print()s.

read BUF, NBYTES, [OFFSET] Instance method. Read some bytes from the scalar. Returns the number of bytes actually read, 0 on end-of-file, undef on error.
write BUF, NBYTES, [OFFSET] Instance method. Write some bytes to the scalar.
sysread BUF, LEN, [OFFSET] Instance method. Read some bytes from the scalar. Returns the number of bytes actually read, 0 on end-of-file, undef on error.
syswrite BUF, NBYTES, [OFFSET] Instance method. Write some bytes to the scalar.

    Seeking/telling and other attributes

autoflush Instance method. No-op, provided for OO compatibility.
binmode Instance method. No-op, provided for OO compatibility.
clearerr Instance method. Clear the error and EOF flags. A no-op.
eof Instance method. Are we at end of file?
seek OFFSET, WHENCE Instance method. Seek to a given position in the stream.
sysseek OFFSET, WHENCE Instance method. Identical to seek OFFSET, WHENCE, q.v.
tell Instance method. Return the current position in the stream, as a numeric offset.
use_RS [YESNO] Instance method. <B>Deprecated and ignored.B> Obey the current setting of $/, like IO::Handle does? Default is false in 1.x, but cold-welded true in 2.x and later.
setpos POS Instance method. Set the current position, using the opaque value returned by getpos().
getpos Instance method. Return the current position in the string, as an opaque object.
sref Instance method. Return a reference to the underlying scalar.


Perl’s TIEHANDLE spec was incomplete prior to 5.005_57; it was missing support for seek(), tell(), and eof(). Attempting to use these functions with an IO::Scalar will not work prior to 5.005_57. IO::Scalar will not have the relevant methods invoked; and even worse, this kind of bug can lie dormant for a while. If you turn warnings on (via $^W or perl -w), and you see something like this...

    attempt to seek on unopened filehandle

...then you are probably trying to use one of these functions on an IO::Scalar with an old Perl. The remedy is to simply use the OO version; e.g.:

    $SH->seek(0,0);    ### GOOD: will work on any 5.005
    seek($SH,0,0);     ### WARNING: will only work on 5.005_57 and beyond


$Id:,v 1.6 2005/02/10 21:21:53 dfs Exp $


    Primary Maintainer

David F. Skoll (

    Principal author

Eryq ( President, ZeeGee Software Inc (

    Other contributors

The full set of contributors always includes the folks mentioned in CHANGE LOG in IO::Stringy. But just the same, special thanks to the following individuals for their invaluable contributions (if I’ve forgotten or misspelled your name, please email me!):

Andy Glew, for contributing getc().

Brandon Browning, for suggesting opened().

David Richter, for finding and fixing the bug in PRINTF().

Eric L. Brine, for his offset-using read() and write() implementations.

Richard Jones, for his patches to massively improve the performance of getline() and add sysread and syswrite.

B. K. Oxley (binkley), for stringification and inheritance improvements, and sundry good ideas.

Doug Wilson, for the IO::Handle inheritance and automatic tie-ing.


IO::String, which is quite similar but which was designed more-recently and with an IO::Handle-like interface in mind, so you could mix OO- and native-filehandle usage without using tied().

Note: as of version 2.x, these classes all work like their IO::Handle counterparts, so we have comparable functionality to IO::String.

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perl v5.20.3 TEST::BUILDER::IO::SCALAR (3) 2014-12-28

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