Beefy Boxes and Bandwidth Generously Provided by pair Networks
We don't bite newbies here... much
 
PerlMonks  

Function Split, bug or error in the documentation?

by bojinlund (Prior)
on Jun 24, 2020 at 12:41 UTC ( #11118420=perlquestion: print w/replies, xml ) Need Help??

bojinlund has asked for the wisdom of the Perl Monks concerning the following question:

use strict; use warnings; use 5.010; # from documentation: # ... and each of these: print join(':', split(//, 'abc', 3)), "\n"; print join(':', split(//, 'abc', 4)), "\n"; # produces the output a:b:c . say $^V; say $^O; __DATA__ output: a:b:c a:b:c: v5.30.1

In the second call there is an extra empty string. I am using Windows 10.

Replies are listed 'Best First'.
Re: Function Split, bug or error in the documentation?
by haukex (Bishop) on Jun 24, 2020 at 13:08 UTC

    AFAICT with a quick check, Perl has always behaved as your code shows. It appears this documentation bug was introduced with a rewrite of the split manpage for 5.16 in bd46758. The previous version did not have this issue, it said:

    Empty trailing fields, on the other hand, are produced when there is a match at the end of the string (and when LIMIT is given and is not 0), regardless of the length of the match. For example:
    print join(':', split(//, 'hi there!', -1)), "\n"; print join(':', split(/\W/, 'hi there!', -1)), "\n";
    produce the output 'h:i: :t:h:e:r:e:!:' and 'hi:there:', respectively, both with an empty trailing field.

    You should definitely open a bug report against perlfunc.pod.

Re: Function Split, bug or error in the documentation?
by soonix (Canon) on Jun 24, 2020 at 12:54 UTC
    Same here, (v5.26.1-1 linux). I assume it is documented in this part in split:
    An empty trailing field, on the other hand, is produced when there is a match at the end of EXPR, regardless of the length of the match (of course, unless a non-zero LIMIT is given explicitly, such fields are removed, as in the last example).
Re: Function Split, bug or error in the documentation?
by davies (Prior) on Jun 24, 2020 at 15:30 UTC
Re: Function Split, bug or error in the documentation?
by bojinlund (Prior) on Jul 04, 2020 at 11:15 UTC

    I am trying to understand split and its documentation. To do this I have implement split by using m{} and the variables @- and @+. By this I have found some problems

    This script shows some of them:

    use strict; use warnings; use 5.010; use Data::Dump qw(dump dd ddx); sub split_e { } split_e( // ); # Warning: Use of uninitialized value $_ in pattern match (m//) at pm_ +1.pl ... my @rv = split( //, '' ); # Warning: none my $str = '1-10,20'; my $pat = '(-)|(,)'; @rv = split( $pat, $str ); warn dump @rv; # (1, "-", undef, 10, undef , ",", 20) @rv = $str =~ m{$pat}g; warn dump @rv; # ("-", undef, undef, ",") while ( my $rv = $str =~ m{$pat}gc ) { for my $ix ( 0 .. 99 ) { if ( defined $-[$ix] ) { say sprintf '$ix= %d (%d,%d)<%s>', $ix, $-[$ix], $+[$ix], substr $str, $-[$ix], $+[$ix] - $-[$ix]; } } } say "Strawberry Perl $^V"; say $^O; __DATA__ output: $ix= 0 (1,2)<-> $ix= 1 (1,2)<-> $ix= 0 (4,5)<,> $ix= 2 (4,5)<,> Strawberry Perl v5.30.1 MSWin32

    Questions

    Magic in split

    This split_e( // ); gives the warning: Use of uninitialized value $_ in pattern match (m//) at pm_1.pl ... but this split( // ); does not.

    Is there some magic in split indicate by the /s in /PATTERN/ in the documentation?

    Bug in the variables @- and @+

    I find that the result from split, m{} and when using $-[$ix] $+[$ix] are inconsistent.

    Split gives (1, "-", undef, 10, undef , ",", 20).

    m{} gives ("-", undef, undef, ",").

    Using $-[$ix] $+[$ix] does not include the undefs

    Is this a bug in the last case?

      split_e( // ), short for split_e( $_ =~ m// ), performs a match operation. You want split_e( qr// ).

      split is an operator. And like all operators, it has full control over the syntax of its operands. split /.../, ... is functionally equivalent to split qr/.../, .... Keep in mind that split predates qr//.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://11118420]
Front-paged by Corion
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others romping around the Monastery: (3)
As of 2020-10-27 15:43 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    My favourite web site is:












    Results (257 votes). Check out past polls.

    Notices?