use strict;
use warnings;

my $fileA = <<FILEA;
Thank you for considering me.
Let me tell you straight, there are two file a.txt and b.txt.
I want each line of text in a.txt should be searched
FILEA
my $fileB = <<FILEB;
txt
FILEB

my @words;

open my $bIn, '<', \$fileB or die "Open fileB failed: $!";
while (<$bIn>) {
    chomp;
    push @words, $_;
}
close $bIn;

my $match = join '|', @words;

open my $aIn, '<', \$fileA or die "Open fileA failed: $!";

while (<$aIn>) {
    next unless /\b($match)\b/;
    
    print;
}
close $aIn;