Regular expression to mask strings using string substitution

Question

I would like to use a regular expression to mask all but the first three alphanumeric characters of each word in a string using a mask character (such as "x"), so "1 Buckingham Palace Road, London" would become "1 Bucxxxxxxx Palxxx Roax, Lonxxx".

Keeping the first three characters is easily done using

s/\b(\w{0,3})(.*)\b/$1/g

but I cannot seem to figure out how to insert length($2) times the masking character instead of $2.

Thanks!

Answer 1

C#:

new Regex(@"(?<!\b.{0,2}).").Replace("1 Buckingham Palace Road, London", "x");

Since you say it's language-agnostic, I trust this can be easily ported into your language of choice...

Or, you could just get the length of $2 and fill the x's the old fashioned way.

Answer 2

Positive lookbehind, any word character with three word characters before it gets changed to an X:

s/(?<=\w{3})\w/$1x/g;

example perl script:

my $string = "1 Buckingham Palace Road, London"; 
$string =~ s/(?<=\w{3})\w/$1x/g; 
print qq($string\n);

Answer 3

use warnings;
use strict;

my $string = "1 Buckingham Palace Road, London";

$string =~ s(
  \b(\w{0,3})(\w*)\b
){
  $1 . ( 'x' x length $2 )
}gex;

print $string, "\n";