Do like this:

my $string = '123-4567';
$string =~ s/-//g;
print $string;
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s/<search>/<replace>/g; # the 'g' replaces every occurrence of <search>, not just the first.

Update: This'll work, too:

my $i='123-4567';
my $j;
while( length($i) ){
    $j .= chop( $i );
    chop $j if substr( $j, -1 ) eq '-';
}
print reverse split //, $j;
[download]