在 Perl 中使用正则表达式将 markdown 斜体替换为 html

Question

To convert the markdown italic text $script into html, I've written this:

my $script = "*so what*";
my $res =~ s/\*(.)\*/$1/g;
print "<em>$1</em>\n";

The expected result is:

<em>so what</em>

but it gives:

<em></em>

How to make it give the expected result?

Answer 1

Problems:

• You print the wrong variable.
• You switch variable names halfway through.
• . won't match more than one character.
• You always add one EM element, even if no stars are found.
• You always add one EM element, even if multiple pairs of stars are found.
• You add the EM element around the entire output, not just the portion in stars.

Fix:

$script =~ s{\*([^*]+)\*}{<em>$1</em>}g;
print "$script\n";

or

my $res = $script =~ s{\*([^*]+)\*}{<em>$1</em>}gr;
print "$res\n";

But that's not it. Even with all the aforementioned problems fixed, your parser still has numerous other bugs. For example, it misapplies italics for all of the following:

• **Important**
  Correct: Important
  Your code: * Important *
• 4 * 5 * 6 = 120
  Correct: 4 * 5 * 6 = 120
  Your code: 4 5 6 = 120
• 4 * 6 = 20 is *wrong*
  Correct: 4 * 6 = 20 is wrong
  Your code: 4 6 = 20 is wrong*
• `foo *bar* baz`
  Correct: foo *bar* baz
  Your code: `foo bar baz`
• \*I like stars\*
  Correct: *I like stars*
  Your code: \ I like stars\