qq interpolates no matter what opening and closing characters you use, so characters such as $ and \ will have special meaning in the string. If you don't want anything interpolated into the string, use a heredoc with single quotes:

print <<'END_HTML';
<!DOCTYPE html>
<html>
...
</html>
END_HTML

[download]

However, generating HTML like this is pretty error-prone, as you've discovered. I suggest you look into a templating system such as Template::Toolkit.

As for debugging CGI scripts, you should check your server's logs for the cause of a 500 error. See also CGI Help Guide, Troubleshooting Perl CGI scripts, and your browser's debugging tools to inspect the HTML.

Update: The reason you're seeing a difference between qq|| and qq{}/qq() is that the latter supports nested brackets, so e.g. print qq{a{b}c}; prints a{b}c, whereas qq|a|b| is not valid (hence the 500 error), as the second | terminates the string - you'd have to write qq|a\|b| to get the string "a|b".

In reply to Re: How to print an HTML input tag with its regex pattern in Perl CGI? by haukex
in thread How to print an HTML input tag with its regex pattern in Perl CGI? by underTheRadar

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