++ed by:
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Author image Flavio Poletti

NAME

IO::Slice - restrict reads to a range in a file

VERSION

version 0.2

SYNOPSIS

   use IO::Slice;

   # Define a slice based on a file
   my $sfh = IO::Slice->new(
      filename => '/path/to/file',
      offset   => 13,
      length   => 16,
   );

   # Ditto, based on a previously available filehandle $fh. The
   # filehandle MUST be seekable.
   my $sfh = IO::Slice->new(
      fh     => $fh,
      offset => 13,
      length => 16,
   );

   # Both the filehandle and the filename can be provided. The
   # filehandle will win.
   my $sfh = IO::Slice->new(
      fh       => $fh,
      filename => '/path/to/file',
      offset   => 13,
      length   => 16,
   );

   # Whatever, you can use $sfh as any other filehandle, mostly.

DESCRIPTION

This module allows the definition of a filehandle that only works on a slice of an input file. The new method provides back a GLOB that can be used as any other filehandle, mostly, with the notable exception of some methods like stat, fileno and the tracking of the input lines.

   my $sfh = IO::Slice->new(
      filename => '/path/to/file',
      offset   => 13,
      length   => 16,
   );

The provided handle works only for reading, not for writing.

The parameters that you can pass to the constructor are:

  • the source of data. This can be provided by either a filename (through the filename key) or a filehandle (through the fh key). If both are provided, the filehandle will take precedence for getting the data.

  • the offset, specifying an offset where the slice starts. 0 means the start of the file

  • the length, specifying the number of bytes in the slice

METHODS

new

create a new IO::Slice object.

Parameters can be passed either as an hash reference or key-value pairs. Useful parameters are:

offset

set the offset of the slice from the start of file. This is mandatory

length

set the length of the slice. This is mandatory.

Neither offset nor length are tested for correctness against the file.

You have to provide at least one of fh and filename so that the data source can be reached. If you provide both, fh will used for taking the data.

Returns the object. Throws an exception in case of errors.

open

open a slice. Parameters are the same as the "new" method.

close

close the tied handle and the associated object.

opened

assess whether the object is associated to an opened file

binmode

support the binmode method... but in a fake way, does not accept anything actually.

getc

get one byte from the input stream.

ungetc

release one byte back into the input stream

eof

test whether there are still bytes to read or we are at the end of the file

pos

accessor for the position. It allows you to set the position by passing an input parameter, and to retrieve the current position.

seek

set current position in the stream. Two positional parameters are accepted:

  • offset

    specifies the offset to use

  • whence

    specifies the reference point for applying the offset

Both are consistent with what you find in CORE::seek documentation.

tell

get current position in the stream.

do_read

convenience function around read. Takes as input the count of needed bytes and outputs a string that is the result of the underlying read, without requiring you to provide a buffer.

getline

get a line from the input. Returns a single scalar with one line.

This honors $/ (aka $INPUT_RECORD_SEPARATOR), so line might not be what you generally consider a line.

getlines

list-version for getting lines, propedeutic to READLINE

read

read bytes from the stream. The interface is the same as the CORE::read function, with the following positional parameters:

  • filehandle

    mandatory parameter

  • buffer

    mandatory parameter

  • offset

    optional parameter, used for putting data into the buffer

Returns undef if errors arise or end of file. Returns number of read characters otherwise (0 if end of file).

sysseek

alias of "seek"

sysread

alias for "read"

Nullified Functions

The following functions are defined but don't actually do anything.

print
printflush
printf
fileno
error
clearerr
sync
write
setbuf
setvbuf
untaint
autoflush
fcntl
ioctl
input_line_number

SEE ALSO

This module is heavily inspired (and in some places based) on code from "IO::String" 1.08 by Gisle Aas.

AUTHOR

Flavio Poletti <polettix@cpan.org>

COPYRIGHT AND LICENSE

Copyright (C) 2014 by Flavio Poletti <polettix@cpan.org>

This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0.

This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.