C:\>perl -E "my $str1 = qq(|L|D|); my $str2 = qr(\|L\|);if ($str2 =~ $
+str1) { say 'foo';}"
foo
[download]

Actually, SimonPratt is right. From OP's description ($str2 ["is in"] as a part of $str1) requires a regex test (if used) in the above order.

Update: Added direct quote from OP's spec to clarify my paraphase, "as a part of...."

Nope. If you want to know if string2 is in string1, you need string1 on the left side and string2 on the right side of the binding operator.

$  perl -E 'my $str1 = qq(one two three); my $str2 = qq(two); if ($str
+2 =~ m/$str1/) { say "foo";}'


$  perl -E 'my $str1 = qq(one two three); my $str2 = qq(two); if ($str
+1 =~ m/$str2/) { say "foo";}'
foo
[download]

Your test is wrong for the following reason: if you want to try to put string1 on the right side, then it is string1 that should be a quotemetaed regex or have the pipes escaped:

$ perl -E 'my $str1 = qr(\|L\|D\|);  my $str2 = qq(\|L\|); if ($str2 =
+~ m/$str1/) { say "foo";}'

$ perl -E 'my $str1 = qq(\|L\|D\|);  my $str2 = qr(\|L\|); if ($str1 =
+~ m/$str2/) { say "foo";}'
foo

$ perl -E 'my $str1 = qq(|L|D|);  my $str2 = qq(|L|); if ($str1 =~ m/\
+Q$str2/) { say "foo";}'
foo
[download]

You appear to have (most of) the angels on your side.

So why did the code I showed return true (or "foo")?"



Quis custodiet ipsos custodes. Juvenal, Satires

if ( $str2 =~ /$str1/i ){...

OP stated that the task is to find $str2 in $str1, so that's probably not right.

such as ... escaping them, though that will also be problematic

See davido's answer regarding \Q (as well as quotemeta).

You're quite right, not sure what I was thinking!