#!/usr/bin/perl -w
use strict;

# [A-Za-z0-9.] => unchanged
# " " => "_"
# "-" => "--"
# isolated punctation => "-[a-z0-3]"
# other => "-" . ( [A-Z4-7] | [_89][\w.] )+ . "-"
#                punctuation   _=control, 8,9=8-bit

my $eight1= pack "C*", 0x80..0xBF;
my $eight2= pack "C*", 0xC0..0xFF;
my $ctrl= pack "C*", 0..31,128;
my $punct= q-!"#$%&'()*+,/:;<=>?@[\\]^_`{|}~-;
my $code= join "", '0'..'9','a'..'z','A'..'Z','_','.';

sub encode {
    local( $_ )= shift;
    s{(-|[^-a-zA-Z0-9. ]+)}{
        if(  "-" eq $1  ) {
            "--";
        } elsif(  1 == length($1)  &&  0 <= index($punct,$1)  ) {
            my $p= $1;
            $p =~ tr.!"#$%&'()*+,/:;<=>?@[\\]^_`{|}~.a-z0-3.;
            "-$p";
        } else {
            my $g= $1;
            $g =~ s{([\Q$punct\E])|([$ctrl])|([$eight1])|([$eight2])}{
                my $c= $1 || $2 || $3 || $4;
                if(  $1  ) {
                    $c =~ tr.!"#$%&'()*+,/:;<=>?@[\\]^_`{|}~.A-Z4-7.;
                    $c;
                } elsif(  $2  ) {
                    "_" . substr( $code, index($ctrl,$c), 1 );
                } elsif(  $3  ) {
                    "8" . substr( $code, index($eight1,$c), 1 );
                } else {
                    "9" . substr( $code, index($eight2,$c), 1 );
                }
            }ge;
            "-$g-";
        }
    }ge;
    tr/ /_/;
    return $_;
}

sub decode {
    local( $_ )= shift;
    s{(_)|-(-)|-([a-z0-3])|-((?:[A-Z4-7]|[_89][\w.])+)-}{
        if(  $1  ) {
            " ";
        } elsif(  $2  ) {
            "-";
        } elsif(  ! $4  ) {
            my $g= $3;
            $g =~ tr.a-z0-3.!"#$%&'()*+,/:;<=>?@[\\]^_`{|}~.;
            $g;
        } else {
            my $g= $4;
            $g =~ s{([A-Z4-7])|([_89])([\w.])}{
                #{ local( $^W);
                #    warn "else: 1-($1) 2-($2) 3-($3)\n";
                #}
                my $g= $1 || $3;
                if(  $1  ) {
                    $g =~ tr.A-Z4-7.!"#$%&'()*+,/:;<=>?@[\\]^_`{|}~.;
                    $g;
                } elsif(  "_" eq $2  ) {
                    substr( $ctrl, index($code,$g), 1 );
                } elsif(  "8" eq $2  ) {
                    substr( $eight1, index($code,$g), 1 );
                } else {
                    substr( $eight2, index($code,$g), 1 );
                }
            }ge;
            $g;
        }
    }ge;
    return $_;
}

my $decode= grep /^-d/, @ARGV;
binmode( $decode ? \*STDOUT : \*STDIN );
if(  grep /^-e/, @ARGV  ) {
    my $data= do { local( $/ ); <STDIN> };
    print $decode ? decode($data) : encode($data);
} else {
    while(  <STDIN>  ) {
        s#\r?\n$##;
        print $decode ? decode($_) : encode($_), "\n";
    }
}