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

my (@array,@newarray);

@array=("ABCDEF01","HIJKL678","VWXYZ123H");

print join (" OR ",  map{"USERNAME like $_%"}map{substr($_,0,4)} @array),"\n";

#perhaps better:
print "USERNAME ";
print join (" OR ",  map{"like $_%"}map{substr($_,0,4)} @array),"\n";

__END__
USERNAME like ABCD% OR USERNAME like HIJK% OR USERNAME like VWXY%
USERNAME like ABCD% OR like HIJK% OR like VWXY%