FileHandle(3p) | Perl Programmers Reference Guide | FileHandle(3p)

# NAME

FileHandle - supply object methods for filehandles

# SYNOPSIS

        use FileHandle;
        my $fh = FileHandle->new;
        if ($fh->open("< file")) {
            print <$fh>;
            $fh->close;
        }
        my $fh = FileHandle->new("> FOO");
        if (defined $fh) {
            print $fh "bar\n";
            $fh->close;
        }
        my $fh = FileHandle->new("file", "r");
        if (defined $fh) {
            print <$fh>;
            undef $fh;       # automatically closes the file
        }
        my $fh = FileHandle->new("file", O_WRONLY|O_APPEND);
        if (defined $fh) {
            print $fh "corge\n";
            undef $fh;       # automatically closes the file
        }
        my $pos = $fh->getpos;
        $fh->setpos($pos);
        $fh->setvbuf(my $buffer_var, _IOLBF, 1024);
        my ($readfh, $writefh) = FileHandle::pipe;
        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:

        close
        fileno
        getc
        gets
        eof
        clearerr
        seek
        tell

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

        autoflush
        output_field_separator
        output_record_separator
        input_record_separator
        input_line_number
        format_page_number
        format_lines_per_page
        format_lines_left
        format_name
        format_top_name
        format_line_break_characters
        format_formfeed

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

$fh->print
  See "print" in perlfunc.
$fh->printf
  See "printf" in perlfunc.
$fh->getline
  This works like <$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.

2024-05-14 | perl v5.40.1