How can I declare a regex to split Perl?

Question

Today I came across this Perl construct:

@foo = split("\n", $bar);

This works well for splitting a large string into an array of strings for UNIX-style line endings, but leaves the trailing \ r for Windows. So I changed it to:

@foo = split("\r?\n", $bar);

Which splits a line into lines and does not leave trailing \ r (tested in ActivePerl 5.8). Then I was told that this should probably be:

@foo = split(/\r?\n/, $bar);

So why does the second option work at all? Double quotation marks mean that the content is evaluated, so \ r and \ n are actually treated as CR and LF, but? considered a metacharacter of a regular expression, not a literal question mark.

Are the slashes around the regex just optional for split ()? Is the regular expression supposed to be the first parameter of the function?

Answer 1

split . , .

, / /

Answer 2

- ( ), escape-, .

EDIT: , . :

Perl m, . - , m, :

m/\r?\n/
m"\r?\n"
m$\r?\n$
/\r?\n/

, " ". , escape- .

, , m, , , Arnshea , split , , .

Answer 3

, split ( , ). , . = ~ (, $foo = ~ "pattern" ). , //.

//, , , split ( "|", "a | b | c" ) -.

Answer 4

.

use Modern::Perl;
use Benchmark qw'cmpthese';

# set up some test data
my $bar = join "\n", 'a'..'z';

my $qr  = qr/\r?\n/;
my $str =   "\r?\n";
my $qq  = qq/\r?\n/;

my %test = (
  '   //' =>   sub{ split(   /\r?\n/, $bar ); },
  '  m//' =>   sub{ split(  m/\r?\n/, $bar ); },
  '  m""' =>   sub{ split(  m"\r?\n", $bar ); },
  ' qr//' =>   sub{ split( qr/\r?\n/, $bar ); },
  ' qq//' =>   sub{ split( qq/\r?\n/, $bar ); },
  '   ""' =>   sub{ split(   "\r?\n", $bar ); },
  '$qr  ' =>   sub{ split( $qr,  $bar ); },
  '$str ' =>   sub{ split( $str, $bar ); },
  '$qq  ' =>   sub{ split( $qq,  $bar ); }
);

cmpthese( -5, \%test, 'auto');

Benchmark: running    
    "",    //,   m"",   m//,  qq//,  qr//, $qq  , $qr  , $str  
    for at least 5 CPU seconds...

      "":  6 wallclock secs ( 5.21 usr +  0.02 sys =  5.23 CPU) @ 42325.81/s (n=221364)
      //:  6 wallclock secs ( 5.26 usr +  0.00 sys =  5.26 CPU) @ 42626.24/s (n=224214)
     m"":  6 wallclock secs ( 5.30 usr +  0.01 sys =  5.31 CPU) @ 42519.96/s (n=225781)
     m//:  6 wallclock secs ( 5.20 usr +  0.00 sys =  5.20 CPU) @ 42568.08/s (n=221354)
    qq//:  6 wallclock secs ( 5.24 usr +  0.01 sys =  5.25 CPU) @ 42707.43/s (n=224214)
    qr//:  6 wallclock secs ( 5.11 usr +  0.03 sys =  5.14 CPU) @ 33277.04/s (n=171044)
   $qq  :  5 wallclock secs ( 5.15 usr +  0.00 sys =  5.15 CPU) @ 42154.76/s (n=217097)
   $qr  :  4 wallclock secs ( 5.28 usr +  0.00 sys =  5.28 CPU) @ 39593.94/s (n=209056)
   $str :  6 wallclock secs ( 5.29 usr +  0.00 sys =  5.29 CPU) @ 41843.86/s (n=221354)


         Rate  qr//   $qr  $str   $qq    ""   m""   m//    //  qq//
 qr// 33277/s    --  -16%  -20%  -21%  -21%  -22%  -22%  -22%  -22%
$qr   39594/s   19%    --   -5%   -6%   -6%   -7%   -7%   -7%   -7%
$str  41844/s   26%    6%    --   -1%   -1%   -2%   -2%   -2%   -2%
$qq   42155/s   27%    6%    1%    --   -0%   -1%   -1%   -1%   -1%
   "" 42326/s   27%    7%    1%    0%    --   -0%   -1%   -1%   -1%
  m"" 42520/s   28%    7%    2%    1%    0%    --   -0%   -0%   -0%
  m// 42568/s   28%    8%    2%    1%    1%    0%    --   -0%   -0%
   // 42626/s   28%    8%    2%    1%    1%    0%    0%    --   -0%
 qq// 42707/s   28%    8%    2%    1%    1%    0%    0%    0%    --

, , qr// . qr// $qr . .

, split().

Answer 5

split("\r?\n", $bar) : split , . perl perldoc -f split.

split(/\r?\n/, $bar).