Why can't I set $LIST_SEPARATOR in Perl?

Question

I want to set the LIST_SEPARATOR in perl, but all I get is this warning:

Name "main::LIST_SEPARATOR" used only once: possible typo at ldapflip.pl line 7.

Here is my program:

#!/usr/bin/perl -w

@vals;
push @vals, "a";
push @vals, "b";

$LIST_SEPARATOR='|';

print "@vals\n";

I am sure I am missing something obvious, but I don't see it.

Thanks

Answer 1

perlvar is your friend:

• $LIST_SEPARATOR
• $"

This is like $, except that it applies to array and slice values interpolated into a double-quoted string (or similar interpreted string). Default is a space. (Mnemonic: obvious, I think.)

$LIST_SEPARATOR is only avaliable if you use English; If you don't want to use English; in all your programs, use $" instead. Same variable, just with a more terse name.

Answer 2

Only the mnemonic is available

$" = '|';

unless you

use English;

first.

As described in perlvar. Read the docs, please.

The following names have special meaning to Perl. Most punctuation names have reasonable mnemonics, or analogs in the shells. Nevertheless, if you wish to use long variable names, you need only say

use English;

at the top of your program. This aliases all the short names to the long names in the current package. Some even have medium names, generally borrowed from awk. In general, it's best to use the

use English '-no_match_vars';

invocation if you don't need $PREMATCH, $MATCH, or $POSTMATCH, as it avoids a certain performance hit with the use of regular expressions. See English.

Answer 3

you SHOULD use the strict pragma:

use strict;

you might want to use the diagnostics pragma to get additional hits about the warnings (that you already have enabled with the -w flag):

use diagnostics;

Answer 4

Slightly off-topic (the question is already well answered), but I don't get the attraction of English.

Cons:

• A lot more typing
• Names not more obvious (ie, I still have to look things up)

Pros:

• ?

I can see the benefit for other readers - especially people who don't know Perl very well at all. But in that case, if it's a question of making code more readable later, I would rather this:

{
  local $" = '|'; # Set interpolated list separator to '|'
  # fun stuff here...
}