Perl 5 version documentation

IO::Seekable

NAME

IO::Seekable - supply seek based methods for I/O objects

SYNOPSIS

  1.     use IO::Seekable;
  2.     package IO::Something;
  3.     @ISA = qw(IO::Seekable);

DESCRIPTION

IO::Seekable does not have a constructor of its own as it is intended to be inherited by other IO::Handle based objects. It provides methods which allow seeking of the file descriptors.

  • $io->getpos

    Returns an opaque value that represents the current position of the IO::File, or undef if this is not possible (eg an unseekable stream such as a terminal, pipe or socket). If the fgetpos() function is available in your C library it is used to implements getpos, else perl emulates getpos using C's ftell() function.

  • $io->setpos

    Uses the value of a previous getpos call to return to a previously visited position. Returns "0 but true" on success, undef on failure.

See perlfunc for complete descriptions of each of the following supported IO::Seekable methods, which are just front ends for the corresponding built-in functions:

  • $io->seek ( POS, WHENCE )

    Seek the IO::File to position POS, relative to WHENCE:

    • WHENCE=0 (SEEK_SET)

      POS is absolute position. (Seek relative to the start of the file)

    • WHENCE=1 (SEEK_CUR)

      POS is an offset from the current position. (Seek relative to current)

    • WHENCE=2 (SEEK_END)

      POS is an offset from the end of the file. (Seek relative to end)

    The SEEK_* constants can be imported from the Fcntl module if you don't wish to use the numbers 1 or 2 in your code.

    Returns 1 upon success, otherwise.

  • $io->sysseek( POS, WHENCE )

    Similar to $io->seek, but sets the IO::File's position using the system call lseek(2) directly, so will confuse most perl IO operators except sysread and syswrite (see perlfunc for full details)

    Returns the new position, or undef on failure. A position of zero is returned as the string "0 but true"

  • $io->tell

    Returns the IO::File's current position, or -1 on error.

SEE ALSO

perlfunc, I/O Operators in perlop, IO::Handle IO::File

HISTORY

Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>