Perl 5 version 26.3 documentation

FileHandle

NAME

FileHandle - supply object methods for filehandles

SYNOPSIS

  1.     use FileHandle;
  3.     $fh = FileHandle->new;
  4.     if ($fh->open("< file")) {
  5.         print <$fh>;
  6.         $fh->close;
  7.     }
  9.     $fh = FileHandle->new("> FOO");
  10.     if (defined $fh) {
  11.         print $fh "bar\n";
  12.         $fh->close;
  13.     }
  15.     $fh = FileHandle->new("file", "r");
  16.     if (defined $fh) {
  17.         print <$fh>;
  18.         undef $fh;       # automatically closes the file
  19.     }
  21.     $fh = FileHandle->new("file", O_WRONLY|O_APPEND);
  22.     if (defined $fh) {
  23.         print $fh "corge\n";
  24.         undef $fh;       # automatically closes the file
  25.     }
  27.     $pos = $fh->getpos;
  28.     $fh->setpos($pos);
  30.     $fh->setvbuf($buffer_var, _IOLBF, 1024);
  32.     ($readfh, $writefh) = FileHandle::pipe;
  34.     autoflush STDOUT 1;

DESCRIPTION

NOTE: This class is now a front-end to the IO::* classes.

FileHandle::new creates a FileHandle , which is a reference to a newly created symbol (see the Symbol package). If it receives any parameters, they are passed to FileHandle::open ; if the open fails, the FileHandle object is destroyed. Otherwise, it is returned to the caller.

FileHandle::new_from_fd creates a FileHandle like new does. It requires two parameters, which are passed to FileHandle::fdopen ; if the fdopen fails, the FileHandle object is destroyed. Otherwise, it is returned to the caller.

FileHandle::open accepts one parameter or two. With one parameter, it is just a front end for the built-in open function. With two parameters, the first parameter is a filename that may include whitespace or other special characters, and the second parameter is the open mode, optionally followed by a file permission value.

If FileHandle::open receives a Perl mode string (">", "+<", etc.) or a POSIX fopen() mode string ("w", "r+", etc.), it uses the basic Perl open operator.

If FileHandle::open is given a numeric mode, it passes that mode and the optional permissions value to the Perl sysopen operator. For convenience, FileHandle::import tries to import the O_XXX constants from the Fcntl module. If dynamic loading is not available, this may fail, but the rest of FileHandle will still work.

FileHandle::fdopen is like open except that its first parameter is not a filename but rather a file handle name, a FileHandle object, or a file descriptor number.

If the C functions fgetpos() and fsetpos() are available, then FileHandle::getpos returns an opaque value that represents the current position of the FileHandle, and FileHandle::setpos uses that value to return to a previously visited position.

If the C function setvbuf() is available, then FileHandle::setvbuf sets the buffering policy for the FileHandle. The calling sequence for the Perl function is the same as its C counterpart, including the macros _IOFBF , _IOLBF , and _IONBF , except that the buffer parameter specifies a scalar variable to use as a buffer. WARNING: A variable used as a buffer by FileHandle::setvbuf must not be modified in any way until the FileHandle is closed or until FileHandle::setvbuf is called again, or memory corruption may result!

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

  1.     close
  2.     fileno
  3.     getc
  4.     gets
  5.     eof
  6.     clearerr
  7.     seek
  8.     tell

See perlvar for complete descriptions of each of the following supported FileHandle methods:

  1.     autoflush
  2.     output_field_separator
  3.     output_record_separator
  4.     input_record_separator
  5.     input_line_number
  6.     format_page_number
  7.     format_lines_per_page
  8.     format_lines_left
  9.     format_name
  10.     format_top_name
  11.     format_line_break_characters
  12.     format_formfeed

Furthermore, for doing normal I/O you might need these:

  • $fh->print

    See print.

  • $fh->printf

    See printf.

  • $fh->getline

    This works like <$fh> described in I/O Operators in perlop except that it's more readable and can be safely called in a list context but still returns just one line.

  • $fh->getlines

    This works like <$fh> when called in a list context to read all the remaining lines in a file, except that it's more readable. It will also croak() if accidentally called in a scalar context.

There are many other functions available since FileHandle is descended from IO::File, IO::Seekable, and IO::Handle. Please see those respective pages for documentation on more functions.

SEE ALSO

The IO extension, perlfunc, I/O Operators in perlop.