Split, variable delimiter

Heath

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Feb 21, 2006, 1:11:56 PM2/21/06

to

Hello,

I'm using perl v5.8.7.

When $_ is set to something like "\t\t\t4.34\t4.65\t3.25\t9.54\n",
I do the following:

my @line = split ' ';
print "$#line, $line[0]\n";

And get what I expect:

3, 4.34

But when I do this:

my $delim = ' ';
my @line = split $delim;
print "$#line, $line[0]\n";
if ($line[0] eq $_) {print "Equal\n"; }

I get this:

0, 4.34 4.65
3.25 9.54

Equal

Which is not exactly what I'm after. So, why are these two
snippets behaving differently? What can I do to make them
equivalent?

I'm probably missing something obvious. If so, please be nice. ;)

use...@davidfilmer.com

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Feb 21, 2006, 1:43:08 PM2/21/06

to

Heath wrote:
> my $delim = ' ';
> my @line = split $delim;

You still need delims around your delim. Try something like /$delim/

--
http://DavidFilmer.com

it_says_BALLS_on_your forehead

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Feb 21, 2006, 2:25:58 PM2/21/06

to

Heath wrote:
> Hello,
>
> I'm using perl v5.8.7.
>
> When $_ is set to something like "\t\t\t4.34\t4.65\t3.25\t9.54\n",
> I do the following:
>
> my @line = split ' ';
> print "$#line, $line[0]\n";
>
> And get what I expect:
>
> 3, 4.34
>
> But when I do this:
>
> my $delim = ' ';
> my @line = split $delim;
> print "$#line, $line[0]\n";
> if ($line[0] eq $_) {print "Equal\n"; }
>
> I get this:
>
> 0, 4.34 4.65
> 3.25 9.54
>
> Equal
>
> Which is not exactly what I'm after. So, why are these two
> snippets behaving differently? What can I do to make them
> equivalent?

first, look at: perldoc -f split | more
or, browser-friendly:
http://www.physiol.ox.ac.uk/Computing/Online_Documentation/Perl-5.8.6/functions/split.html

see the part about the special case of split ' '

i would say the best thing to do would be not to use split ' ' at all.
==============
use strict; use warnings;

$_ = "\t\t\t4.34\t4.65\t3.25\t9.54\n";

$_ =~ s/^\s+//;

my @line = split /\s/;

print "$#line, $line[0]\n";

my $delim = '\s';
my @line2 = split /$delim/;
print "$#line2, $line2[0]\n";

Heath

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Feb 21, 2006, 2:26:24 PM2/21/06

to

I've tried using $delim, /$delim/, "$delim", '$delim', and even
"\'$delim\'". All do the same as when using $delim.

Heath

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Feb 21, 2006, 3:50:06 PM2/21/06

to

it_says_BALLS_on_your forehead wrote:
> first, look at: perldoc -f split | more
> or, browser-friendly:
> http://www.physiol.ox.ac.uk/Computing/Online_Documentation/Perl-5.8.6/functions/split.html
>
> see the part about the special case of split ' '

Yes, I read through that before I ever posted. The behavior I'm
after is that of [split ' ']. I don't get that behavior when I pass
the space char to split via a variable. I would simply just like to
know why that is and how I can get that behavior by passing a variable,
if it is possible at all.

> i would say the best thing to do would be not to use split ' ' at all.
> ==============
> use strict; use warnings;
>
> $_ = "\t\t\t4.34\t4.65\t3.25\t9.54\n";
>
> $_ =~ s/^\s+//;
>
> my @line = split /\s/;
> print "$#line, $line[0]\n";
>
> my $delim = '\s';
> my @line2 = split /$delim/;
> print "$#line2, $line2[0]\n";

This works great, but it accomplishes the exact same thing as:

==============
use strict; use warnings;

$_ = "\t\t\t4.34\t4.65\t3.25\t9.54\n";

my @line = split;

print "$#line, $line[0]\n";

==============

All I need is a value to assign to $delim such that a [split $delim]
will give me the same behavior as a [split].

Uri Guttman

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Feb 21, 2006, 3:58:06 PM2/21/06

to

>>>>> "H" == Heath <hdew...@maxtc.com> writes:

H> Yes, I read through that before I ever posted. The behavior I'm
H> after is that of [split ' ']. I don't get that behavior when I pass
H> the space char to split via a variable. I would simply just like to
H> know why that is and how I can get that behavior by passing a variable,
H> if it is possible at all.

rtfm some more:

As a special case, specifying a PATTERN of space
(' ') will split on white space just as "split" with
no arguments does. Thus, "split(' ')" can be used
to emulate awk's default behavior, ...

note that PATTERN is the actual literal passed to split so it can't be a
variable. otherwise how could it tell / / from ' ' from $foo = ' '? this
is a very odd way to get that special behavior as it is inband and very
special cased. if you must have that vs other splits on demand, use a
sub to handle your cased and do 2 different splits based on $foo eq '
'. or use code refs for each split type. many ways to handle it.

H> All I need is a value to assign to $delim such that a [split $delim]
H> will give me the same behavior as a [split].

can't be done. so choose another solution.

uri

--
Uri Guttman ------ u...@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org

robic0

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Feb 21, 2006, 5:51:29 PM2/21/06

to

It is a bug (I mean a feature) of split. According to the docs
the Perl parser seems to look for the single quoted space ' ' and that
differentiates it from a space " " as a pattern. So obviously the single
quote is as significant as the space. However, the 3 character string is
parsed as a first level parse. So you can't even assign $delim = "' '" or
$delim = "" (null string) ... which is a special case as well ass the ' '.

It would appear to be a very useful case since it populates every array position
with a non-whitespace. If you want to run dynamic patterns, the ' ' case will have
to be an exclusion, tested for and hardcoded.

ie: if ($delim ne ' ') {split $delim;} else {split ' '}

Quote:

As a special case, specifying a PATTERN of space (' ') will split on white space
just as split with no arguments does. Thus, split(' ') can be used to emulate awk's

default behavior, whereas split(/ /) will give you as many null initial fields as
there are leading spaces. A split on /\s+/ is like a split(' ') except that any
leading whitespace produces a null first field. A split with no arguments really
does a split(' ', $_) internally.

Some code:

use strict;
use warnings;

$_ = "\t\t\t4.34\t4.65\t3.25\t9.54\n";

my @line = split /' '/;
print "$#line", @line, "\n";