Why does adding the Perl /x switch stop my regex from matching?

Question

I'm trying to match: ``` JOB: fruit 342 apples to get ``` The code matches: ``` $line =~ /^JOB: fruit (\d+) apples to get/ ``` But, when I add the `/x` switch in: ``` $line =~ /^JOB: fruit (\d+) apples to get/x ``` It does not match. I looked into the `/x` switch, and it says it just lets you do comments. I don't know why adding `/x` stops my regex from matching.

Accepted Answer

The `/x` modifier tells Perl to ignore most whitespace that isn't escaped in the regex.

For example, let's just focus on `apples to get`. You could match it with:

```
$line =~ /apples to get/
```

But if you try:

```
$line =~ /apples to get/x
```

then Perl will ignore the spaces. So it would be like trying to match `applestoget`.

You can read more about it in perlre. They have this nice example of how you can use the modifier to make the code more readable.

```
 # Delete (most) C comments.
$program =~ s {
        /\* # Match the opening delimiter.
        .*? # Match a minimal number of characters.
        \*/ # Match the closing delimiter.
} []gsx;
```

They also mention how to match whitespace or `#` again while using the `/x` modifier.

Use of /x means that if you want real whitespace or # characters in the pattern (outside a bracketed character class, which is unaffected by /x), then you'll either have to escape them (using backslashes or \Q...\E ) or encode them using octal, hex, or \N{} escapes.

Why does adding the Perl /x switch stop my regex from matching?

Solution

Problem