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Top Forums Shell Programming and Scripting Perl write and read on same file Post 302845615 by royalibrahim on Thursday 22nd of August 2013 02:43:45 AM
Old 08-22-2013
Perl write and read on same file

Hi,

I am trying to do a write operation followed by a read operation on the same file through Perl, expecting the output produced by read to contain the new lines added, as follows:

Code:
#! /usr/bin/perl -w

open FH, "+< testfile" or die "$@";
print FH  "New content added\n";
while (my $line = <FH>) {
    print "$line";
}
close(FH);

but the above code is sometimes corrupting the file's data (like replacing, globbering spaces etc.,). I have tried to flush the buffer but to no avail:
Code:
open FH, "+>> testfile" or die "$@";
$| = 1;
print FH  "New content added\n";
while (my $line = <FH>) {
    print "$line";
}
FH->autoflush(1);
close(FH);

I have even changed the mode to '+>', '+>>', but nothing works (i.e) the output is not printed with the lines recently added unless I close the file handle and reopen the file for reading.

Kindly help me how to modify the above Perl code to see the contents that are added by the previous write operation without closing the handle. Thank you.
 

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IO::Async::Socket(3pm)					User Contributed Perl Documentation				    IO::Async::Socket(3pm)

NAME
"IO::Async::Socket" - event callbacks and send buffering for a socket filehandle SYNOPSIS
use IO::Async::Socket; use IO::Async::Loop; my $loop = IO::Async::Loop->new; $loop->connect( host => "some.host.here", service => "echo", socktype => 'dgram', on_connected => sub { my ( $sock ) = @_; my $socket = IO::Async::Socket->new( handle => $sock, on_recv => sub { my ( $self, $dgram, $addr ) = @_; print "Received reply: $dgram ", $loop->stop; }, on_recv_error => sub { my ( $self, $errno ) = @_; die "Cannot recv - $errno "; }, ); $loop->add( $socket ); $socket->send( "A TEST DATAGRAM" ); }, on_resolve_error => sub { die "Cannot resolve - $_[0] "; }, on_connect_error => sub { die "Cannot connect "; }, ); $loop->run; DESCRIPTION
This subclass of IO::Async::Handle contains a socket filehandle. It provides a queue of outgoing data. It invokes the "on_recv" handler when new data is received from the filehandle. Data may be sent to the filehandle by calling the "send" method. It is primarily intended for "SOCK_data" or "SOCK_RAW" sockets; for "SOCK_STREAM" sockets an instance of IO::Async::Stream is probably more appropriate. EVENTS
The following events are invoked, either using subclass methods or CODE references in parameters: on_recv $data, $addr Invoke on receipt of a packet, datagram, or stream segment. The "on_recv" handler is invoked once for each packet, datagram, or stream segment that is received. It is passed the data itself, and the sender's address. on_recv_error $errno Optional. Invoked when the "recv" method on the receiving handle fails. on_send_error $errno Optional. Invoked when the "send" method on the sending handle fails. The "on_recv_error" and "on_send_error" handlers are passed the value of $! at the time the error occured. (The $! variable itself, by its nature, may have changed from the original error by the time this handler runs so it should always use the value passed in). If an error occurs when the corresponding error callback is not supplied, and there is not a subclass method for it, then the "close" method is called instead. on_outgoing_empty Optional. Invoked when the sending data buffer becomes empty. PARAMETERS
The following named parameters may be passed to "new" or "configure": read_handle => IO The IO handle to receive from. Must implement "fileno" and "recv" methods. write_handle => IO The IO handle to send to. Must implement "fileno" and "send" methods. handle => IO Shortcut to specifying the same IO handle for both of the above. on_recv => CODE on_recv_error => CODE on_outgoing_empty => CODE on_send_error => CODE autoflush => BOOL Optional. If true, the "send" method will atempt to send data to the operating system immediately, without waiting for the loop to indicate the filehandle is write-ready. recv_len => INT Optional. Sets the buffer size for "recv" calls. Defaults to 64 KiB. recv_all => BOOL Optional. If true, repeatedly call "recv" when the receiving handle first becomes read-ready. By default this is turned off, meaning at most one fixed-size buffer is received. If there is still more data in the kernel's buffer, the handle will stil be readable, and will be received from again. This behaviour allows multiple streams and sockets to be multiplexed simultaneously, meaning that a large bulk transfer on one cannot starve other filehandles of processing time. Turning this option on may improve bulk data transfer rate, at the risk of delaying or stalling processing on other filehandles. send_all => INT Optional. Analogous to the "recv_all" option, but for sending. When "autoflush" is enabled, this option only affects deferred sending if the initial attempt failed. The condition requiring an "on_recv" handler is checked at the time the object is added to a Loop; it is allowed to create a "IO::Async::Socket" object with a read handle but without a "on_recv" handler, provided that one is later given using "configure" before the stream is added to its containing Loop, either directly or by being a child of another Notifier already in a Loop, or added to one. METHODS
$socket->send( $data, $flags, $addr ) This method adds a segment of data to be sent, or sends it immediately, according to the "autoflush" parameter. $flags and $addr are optional. If the "autoflush" option is set, this method will try immediately to send the data to the underlying filehandle, optionally using the given flags and destination address. If this completes successfully then it will have been sent by the time this method returns. If it fails to send, then the data is queued as if "autoflush" were not set, and will be flushed as normal. SEE ALSO
o IO::Handle - Supply object methods for I/O handles AUTHOR
Paul Evans <leonerd@leonerd.org.uk> perl v5.14.2 2012-10-24 IO::Async::Socket(3pm)
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