# charset="CP932"
# encode="CP932"
# Space を Tab に

#!/usr/bin/perl -wni~
# JPerl 以外では Text::Tabs
use integer;
BEGIN {
	$tabstop ||= 8;
}
1 while s/^([^\t]+)(\t+)/$1 . "\x20" x (length($2) * $tabstop - length($1) % $tabstop)/em;
@_ = unpack "a$tabstop" x (length($_) / $tabstop) . "a*", $_;
print map(s/\x20+$/\t/, @_[0 .. -2]), ($_[-1] eq "\x20" x $tabstop) ? "\t" : $_[-1];
__END__

#!/opt/local/bin/gawk -f
BEGIN {
	tabstop = 8;
	spaces = "                                                                                ";
}
{
	while (match($0, /\t+/))
		sub(/\t+/, substr(spaces, 1, RLENGTH * tabstop - (RSTART - 1) % tabstop));
	while (length($0) > tabstop) {
		str = substr($0, 1, tabstop);
		sub(/\x20\x20+$/, "\t", str);
		printf "%s", str;
		$0 = substr($0, tabstop + 1);
	}
	print;
}