#!/usr/bin/perl -w
# virt-cat
# Copyright (C) 2009-2010 Red Hat Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

use warnings;
use strict;

use Sys::Guestfs;
use Sys::Guestfs::Lib qw(open_guest);
use Pod::Usage;
use Getopt::Long;
use File::Basename;
use Locale::TextDomain 'libguestfs';

=encoding utf8

=head1 NAME

virt-cat - Display a file in a virtual machine

=head1 SYNOPSIS

 virt-cat [--options] domname file

 virt-cat [--options] disk.img [disk.img ...] file

=head1 DESCRIPTION

C<virt-cat> is a command line tool to display the contents of C<file>
where C<file> exists in the named virtual machine (or disk image).

C<virt-cat> can be used to quickly view a single file.  To edit a
file, use C<virt-edit>.  For more complex cases you should look at the
L<guestfish(1)> tool.

=head1 EXAMPLES

Display C</etc/fstab> file from inside the libvirt VM called
C<mydomain>:

 virt-cat mydomain /etc/fstab

List syslog messages from a VM:

 virt-cat mydomain /var/log/messages | tail

Find out what DHCP IP address a VM acquired:

 virt-cat mydomain /var/log/messages | grep 'dhclient: bound to' | tail

Find out what packages were recently installed:

 virt-cat mydomain /var/log/yum.log | tail

Find out who is logged on inside a virtual machine:

 virt-cat mydomain /var/run/utmp > /tmp/utmp
 who /tmp/utmp

or who was logged on:

 virt-cat mydomain /var/log/wtmp > /tmp/wtmp
 last -f /tmp/wtmp

=head1 OPTIONS

=over 4

=cut

my $help;

=item B<--help>

Display brief help.

=cut

my $version;

=item B<--version>

Display version number and exit.

=cut

my $uri;

=item B<--connect URI> | B<-c URI>

If using libvirt, connect to the given I<URI>.  If omitted, then we
connect to the default libvirt hypervisor.

If you specify guest block devices directly, then libvirt is not used
at all.

=cut

my $format;

=item B<--format> raw

Specify the format of disk images given on the command line.  If this
is omitted then the format is autodetected from the content of the
disk image.

If disk images are requested from libvirt, then this program asks
libvirt for this information.  In this case, the value of the format
parameter is ignored.

If working with untrusted raw-format guest disk images, you should
ensure the format is always specified.

=back

=cut

GetOptions ("help|?" => \$help,
            "version" => \$version,
            "connect|c=s" => \$uri,
            "format=s" => \$format,
    ) or pod2usage (2);
pod2usage (1) if $help;
if ($version) {
    my $g = Sys::Guestfs->new ();
    my %h = $g->version ();
    print "$h{major}.$h{minor}.$h{release}$h{extra}\n";
    exit
}

pod2usage (__"virt-cat: no image, VM names or filenames to cat given")
    if @ARGV <= 1;

my $filename = pop @ARGV;

my $g;
if ($uri) {
    $g = open_guest (\@ARGV, address => $uri, format => $format);
} else {
    $g = open_guest (\@ARGV, format => $format);
}

$g->launch ();

my @roots = $g->inspect_os ();
if (@roots == 0) {
    die __x("{prog}: No operating system could be detected inside this disk image.\n\nThis may be because the file is not a disk image, or is not a virtual machine\nimage, or because the OS type is not understood by libguestfs.\n\nIf you feel this is an error, please file a bug report including as much\ninformation about the disk image as possible.\n",
            prog => basename ($0));
}
if (@roots > 1) {
    die __x("{prog}: multiboot operating systems are not supported.\n",
            prog => basename ($0))
}
my %fses = $g->inspect_get_mountpoints ($roots[0]);
my @fses = sort { length $a <=> length $b } keys %fses;
foreach (@fses) {
    $g->mount_ro ($fses{$_}, $_);
}

# Allow this to fail in case eg. the file does not exist.
# NB: https://bugzilla.redhat.com/show_bug.cgi?id=501888
print $g->download($filename, "/dev/stdout");

=head1 SHELL QUOTING

Libvirt guest names can contain arbitrary characters, some of which
have meaning to the shell such as C<#> and space.  You may need to
quote or escape these characters on the command line.  See the shell
manual page L<sh(1)> for details.

=head1 SEE ALSO

L<guestfs(3)>,
L<guestfish(1)>,
L<virt-edit(1)>,
L<Sys::Guestfs(3)>,
L<Sys::Guestfs::Lib(3)>,
L<Sys::Virt(3)>,
L<http://libguestfs.org/>.

=head1 AUTHOR

Richard W.M. Jones L<http://people.redhat.com/~rjones/>

=head1 COPYRIGHT

Copyright (C) 2009 Red Hat Inc.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.