This solution doesn't work since map assigns the return value of clean() to the array. clean() will return the result of the last line which is either 1 or '' for this string. You can make it work by adding $_ in the map block. Not sure if the op wanted the empty final value but they provided a variable for it.

#!/usr/bin/perl
use strict;
use warnings;

my $str = "item1  | item2| item3 
|item4|
 ";

my @cleaned = map { clean($_) } split( /\|/, $str ); 

print ">$_<\n" foreach @cleaned;
print "*"x75,"\n";

my @cleaned2 = map { clean($_);$_ } split( /\|/, $str ); 

print ">$_<\n" foreach @cleaned2;

sub clean
{
    chomp($_[0]);
    $_[0] =~ s/^\s+//;
    $_[0] =~ s/\s+$//;
}


>1<
><
>1<
><
><
**********************************************************************
+*****
>item1<
>item2<
>item3<
>item4<
><
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