#! perl -slw
use strict;

my $search_string = 'uekasdh';

# Split the search string into chars and intersperse
# them with the "ignore whitespace" regex.
my $re =  join '\s*', split '', $search_string;

my $data = do{ local $/; <DATA> }; # Slurp the data
$data =~ s[$re][jjjjjjjj];         # Find and replace.

print $data;