#!/usr/bin/perl -w
# This script takes a command-line arg of a source directory
# that will be passed to rsync, and generates a set of excludes
# that will exclude all mount points from the list.  This is
# useful if you have "bind" mounts since the --one-file-system
# option won't notice the transition to a different spot on
# the same disk.  For example:
#
# mnt-excl /dir | rsync --exclude-from=- ... /dir /dest/
# mnt-excl /dir/ | rsync --exclude-from=- ... /dir/ /dest/
# ssh host mnt-excl /dir | rsync --exclude-from=- ... host:/dir /dest/
#
# Imagine that /dir/foo is a mount point: the first invocation of
# mnt-excl would have output /dir/foo, while the second would have
# output /foo (which are the properly anchored excludes).
#
# NOTE:  This script expects /proc/mounts to exist, but could be
# easily adapted to read /etc/mtab or similar.
#
# ADDENDUM:  The addition of the --filter option (which has support for
# absolute-anchored excludes) has made this script less useful than it
# was.  Beginning with 2.6.4, you can achieve the effect of this script
# through this command:
#
# awk '{print $2}' /proc/mounts | rsync -f 'merge,/- -' host:/dir /dest/

use strict;
use Cwd 'abs_path';

my $file = '/proc/mounts';
my $dir = shift || '/';
$dir = abs_path($dir);
$dir =~ s#([^/]*)$##;
my $trailing = $1;
$trailing = '' if $trailing eq '.' || !-d "$dir$trailing";
$trailing .= '/' if $trailing ne '';

open(IN, $file) or die "Unable to open $file: $!\n";
while (<IN>) {
    $_ = (split)[1];
    next unless s#^\Q$dir$trailing\E##o && $_ ne '';
    print "- /$trailing$_\n";
}
close IN;