This is not a bug, but a feature. Because C<open> mimics the shell in
its style of using redirection arrows to specify how to open the file, it
also does so with respect to extra white space around the filename itself
-as well. For accessing files with naughty names, see L</"Dispelling
-the Dweomer">.
+as well. For accessing files with naughty names, see
+L<"Dispelling the Dweomer">.
=head2 Pipe Opens
character. That's also the case for Perl. The C<open> call
remains the same--just its argument differs.
-If the leading character is a pipe symbol, C<open) starts up a new
+If the leading character is a pipe symbol, C<open> starts up a new
command and open a write-only filehandle leading into that command.
This lets you write into that handle and have what you write show up on
that command's standard input. For example:
because in the traditional C<fork>/C<exec> model, running the other
program happens only in the forked child process, which means that
the failed C<exec> can't be reflected in the return value of C<open>.
-Only a failed C<fork> shows up there. See L<perlfaq8/"Why doesn't open()
-return an error when a pipe open fails?"> to see how to cope with this.
-There's also an explanation in L<perlipc>.
+Only a failed C<fork> shows up there. See
+L<perlfaq8/"Why doesn't open() return an error when a pipe open fails?">
+
to see how to cope with this. There's also an explanation in L<perlipc>.
If you would like to open a bidirectional pipe, the IPC::Open2
-library will handle this for you. Check out L<perlipc/"Bidirectional
-Communication with Another Process">
+library will handle this for you. Check out
+L<perlipc/"Bidirectional Communication with Another Process">
=head2 The Minus File
the standard input. If you open minus for writing, it really means to
access the standard output.
-If minus can be used as the default input or default output? What happens
+If minus can be used as the default input or default output, what happens
if you open a pipe into or out of minus? What's the default command it
-would run? The same script as you're current running! This is actually
-a stealth C<fork> hidden inside an C<open> call. See L<perlipc/"Safe Pipe
-Opens"> for details.
+would run? The same script as you're currently running! This is actually
+a stealth C<fork> hidden inside an C<open> call. See
+L<perlipc/"Safe Pipe Opens"> for details.
=head2 Mixing Reads and Writes
One of the most common uses for C<open> is one you never
even notice. When you process the ARGV filehandle using
-C<E<lt>ARGVE<gt>>, Perl actually does an implicit open
+C<< <ARGV> >>, Perl actually does an implicit open
on each file in @ARGV. Thus a program called like this:
$ myprogram file1 file2 file3
If @ARGV is empty when the loop first begins, Perl pretends you've opened
up minus, that is, the standard input. In fact, $ARGV, the currently
-open file during C<E<lt>ARGVE<gt>> processing, is even set to "-"
+open file during C<< <ARGV> >> processing, is even set to "-"
in these circumstances.
You are welcome to pre-process your @ARGV before starting the loop to
or die "can't open $pwdinfo: $!";
This sort of thing also comes into play in filter processing. Because
-C<E<lt>ARGVE<gt>> processing employs the normal, shell-style Perl C<open>,
+C<< <ARGV> >> processing employs the normal, shell-style Perl C<open>,
it respects all the special things we've already seen:
$ myprogram f1 "cmd1|" - f2 "cmd2|" f3 < tmpfile
@ARGV = map { m#^\w+://# ? "GET $_ |" : $_ } @ARGV;
-It's not for nothing that this is called magic C<E<lt>ARGVE<gt>>.
+It's not for nothing that this is called magic C<< <ARGV> >>.
Pretty nifty, eh?
=head1 Open E<agrave> la C
O_TRUNC Truncate the file
O_NONBLOCK Non-blocking access
-Less common flags that are sometimes available on some operating systems
-include C<O_BINARY>, C<O_TEXT>, C<O_SHLOCK>, C<O_EXLOCK>, C<O_DEFER>,
-C<O_SYNC>, C<O_ASYNC>, C<O_DSYNC>, C<O_RSYNC>, C<O_NOCTTY>, C<O_NDELAY>
-and C<O_LARGEFILE>. Consult your open(2) manpage or its local equivalent
-for details.
+Less common flags that are sometimes available on some operating
+systems include C<O_BINARY>, C<O_TEXT>, C<O_SHLOCK>, C<O_EXLOCK>,
+C<O_DEFER>, C<O_SYNC>, C<O_ASYNC>, C<O_DSYNC>, C<O_RSYNC>,
+C<O_NOCTTY>, C<O_NDELAY> and C<O_LARGEFILE>. Consult your open(2)
+manpage or its local equivalent for details. (Note: starting from
+Perl release 5.6 the O_LARGEFILE flag, if available, is automatically
+added to the sysopen() flags because large files are the default.)
Here's how to use C<sysopen> to emulate the simple C<open> calls we had
before. We'll omit the C<|| die $!> checks for clarity, but make sure
Sometimes you already have a filehandle open, and want to make another
handle that's a duplicate of the first one. In the shell, we place an
ampersand in front of a file descriptor number when doing redirections.
-For example, C<2E<gt>&1> makes descriptor 2 (that's STDERR in Perl)
+For example, C<< 2>&1 >> makes descriptor 2 (that's STDERR in Perl)
be redirected into descriptor 1 (which is usually Perl's STDOUT).
The same is essentially true in Perl: a filename that begins with an
ampersand is treated instead as a file descriptor if a number, or as a
$fd = $ENV{"MHCONTEXTFD"};
open(MHCONTEXT, "<&=$fd") or die "couldn't fdopen $fd: $!";
-If you're using magic C<E<lt>ARGVE<gt>>, you could even pass in as a
-command line argument in @ARGV something like C<"E<lt>&=$MHCONTEXTFD">,
+If you're using magic C<< <ARGV> >>, you could even pass in as a
+command line argument in @ARGV something like C<"<&=$MHCONTEXTFD">,
but we've never seen anyone actually do this.
=head2 Dispelling the Dweomer
proprietary Macintosh system, which uses a colon where the rest of us
use a slash. Maybe C<sysopen> isn't such a bad idea after all.
-If you want to use C<E<lt>ARGVE<gt>> processing in a totally boring
+If you want to use C<< <ARGV> >> processing in a totally boring
and non-magical way, you could do this first:
# "Sam sat on the ground and put his head in his hands.
You've probably noticed how Perl's C<warn> and C<die> functions can
produce messages like:
- Some warning at scriptname line 29, <FH> chunk 7.
+ Some warning at scriptname line 29, <FH> line 7.
That's because you opened a filehandle FH, and had read in seven records
from it. But what was the name of the file, not the handle?
Since you're using the pathname of the file as its handle,
you'll get warnings more like
- Some warning at scriptname line 29, </etc/motd> chunk 7.
+ Some warning at scriptname line 29, </etc/motd> line 7.
=head2 Single Argument Open
Check out Term::ReadKey and Term::ReadLine.
What else can you open? To open a connection using sockets, you won't use
-one of Perl's two open functions. See L<perlipc/"Sockets: Client/Server
-Communication"> for that. Here's an example. Once you have it,
-you can use FH as a bidirectional filehandle.
+one of Perl's two open functions. See
+L<perlipc/"Sockets: Client/Server Communication"> for that. Here's an
+example. Once you have it, you can use FH as a bidirectional filehandle.
use IO::Socket;
local *FH = IO::Socket::INET->new("www.perl.com:80");
it's still easy to get the contents of a document:
use LWP::Simple;
- $doc = get('http://www.sn.no/libwww-perl/');
+ $doc = get('http://www.linpro.no/lwp/');
=head2 Binary Files
Copyright 1998 Tom Christiansen.
-When included as part of the Standard Version of Perl, or as part of
-its complete documentation whether printed or otherwise, this work may
-be distributed only under the terms of Perl's Artistic License. Any
-distribution of this file or derivatives thereof outside of that
-package require that special arrangements be made with copyright
-holder.
+This documentation is free; you can redistribute it and/or modify it
+under the same terms as Perl itself.
Irrespective of its distribution, all code examples in these files are
hereby placed into the public domain. You are permitted and
https://perl5.git.perl.org / perl5.git / blobdiff