$exten=|\.txt|\.doc|\.xml

##</code><code>##

$exten = '|\.txt|\.doc|\.xml';

##</code><code>##

my $exten = '|\.txt|\.doc|\.xml';

for (qw(foo.txt foo.csv foo.xml)) {
  print "$_: ";
  print /$exten/ ? "match" : "no match";
  print "\n";
}

##</code><code>##

foo.txt: match
foo.csv: match
foo.xml: match

##</code><code>##

my $exten = '\.txt|\.doc|\.xml';

for (qw(foo.txt foo.csv foo.xml)) {
  print "$_: ";
  print /$exten/ ? "match" : "no match";
  print "\n";
}

##</code><code>##

foo.txt: match
foo.csv: no match
foo.xml: match