Can I break my Perl regex into multiple lines in my code?

Question

I was just wondering if I am able to break up a long regular expression that I have in my Perl code so that it is written over several lines? I just want the readability an

Answer 1

Use the Whitespace-Insensitive Modifier

The perlre(1) manual page says:

The "/x" modifier itself needs a little more explanation. It tells the regular expression parser to ignore most whitespace that is neither backslashed nor within a character class. You can use this to break up your regular expression into (slightly) more readable parts.

You can use this to create multiline expressions. For example:

/
  abcde_abcde_abdcae_adafdf_    # Have some comments, too. 
  abscd_casdf_asdfd_....asdfaf  # Here's your second line.
/x

Literal Spaces

If your match will contain spaces, you need to make them explicit in your regular expression when using the /x modifier. For example, /foo bar baz quux/x won't match a space-separated string the way you might expect. Instead, you need something like the following:

print "true\n" if
    /
        foo
        \s+  # You need explicit spaces...
        bar
        \s+  # because the modifier will...
        baz
        \s+  # otherwise ignore literal spaces.
        quux
    /x;

Answer 2

Use the + symbol. Here is example:

push @steps, $steps[-1] +
        $radial_velocity * $elapsed_time +
        $orbital_velocity * ($phase + $phase_shift) -
        $DRAG_COEFF * $altitude;

Answer 3

Yep, see the /x modifier in the perlre man page.