c:\@Work\Perl\monks>perl -wMstrict -le
"use constant T => q{UK Mobile - Vodafone [GBRVF] [MSRN]};
 ;;
 my $dest = T;
 $dest =~ s{ \] \s+ \S+ \z }{}xms;
 print qq{2 steps: a: '$dest'};
 ;;
 $dest =~ s{ \W+ }{_}xmsg;
 print qq{2 steps: b: '$dest'};
 ;;
 $dest = T;
 ;;
 $dest =~ s{ \W+ (\w+ \] \z)? }{ $1 ? '' : '_' }xmsge;
 print qq{1 step:     '$dest'};
"
2 steps: a: 'UK Mobile - Vodafone [GBRVF'
2 steps: b: 'UK_Mobile_Vodafone_GBRVF'
1 step:     'UK_Mobile_Vodafone_GBRVF'

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $dest = q{UK Mobile - Vodafone [GBRVF] [MSRN]};
 ;;
 my @xlate = ('', '_');
 ;;
 $dest =~ s{ \W+ (\w+ \] \z)? }{$xlate[! $1]}xmsg;
 print qq{'$dest'};
"
'UK_Mobile_Vodafone_GBRVF'

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $dest = q{UK Mobile - Vodafone [GBRVF] [MSRN]};
 ;;
 $dest =~ tr{A-Za-z}{_}cs;
 $dest =~ s{ _ [^_]+ _ \z }{}xms;
 ;;
 print qq{'$dest'};
"
'UK_Mobile_Vodafone_GBRVF'

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $dest = q{UK Mobile - Vodafone [GBRVF] [MSRN]};
 $dest =~ s{ \W+ (\w+ \] \z)? }{ [ '', '_' ]->[! $1] }xmsge;
 print qq{'$dest'};
"
'UK_Mobile_Vodafone_GBRVF'