fgrep -i -w -f DBtest.txt databaseJoinDan.txt > tableUsed.txt
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Perl code to do something like this (but without all the complex options of grep) could be as follows:

# find_strings.pl

use strict;
use warnings;

my $patfile = shift;
my @pats = do { local @ARGV = ( $patfile ); <> };
chomp @pats;
my $pat = join '|', @pats;

while (<>)
{
    /\b($pat)\b/i and print;
}
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With the above code, invocation would be slightly different from the fgrep solution.

perl find_strings.pl DBtest.txt databaseJoinDan.txt
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(for example).