PerlMonks taught me about Regexp::Assemble, an excellent module for building regex patterns from lists of strings.

#!/usr/bin/env perl
use Modern::Perl;
use Regexp::Assemble;

my @to_remove = qw( is an to for from );
my @strings = ( 'is that true',
                'this is from presentation',
                'to create',
              );
my $re = Regexp::Assemble->new->add(@to_remove);
# say $re; # uncomment to see the regex it makes
map { s/$re//g } @strings; # remove strings anywhere
# map { s/\b$re\b//g } @strings; # or just remove whole words
say for @strings;
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Just a small note. Starting with perl 5.010, you can assemble the stop words into a alternating string separated by the pipe, '|', character and it will use a 'trie' to combine the stop words. It is claimed (by somebody?), the 'trie' approach is big-O 1, an algorithm in constant time (in most cases, they claim). Similiar to what Regexp::Assemble does.

I think I read somewhere that you shouldn't use Regexp::Assemble with perl version > 5.8 because it will muck things up.

@array = qw( is an to  for from);
@strs =("is that true","this is from presentation","to create");
print join("\n",@strs);
print "\nTO DELETE: [@array]";
print "\n------PROCESS--------\n";
foreach $str (@strs)
{
    @words=split(/\s+/,$str);
        print "\nWords in [$str] are [". join(",",@words)."]";
        foreach $word (@words)
        {
            if(grep {$word eq $_} @array)
                {
                        print "\n\tDeleting [$word] from [$str]";
                    $str=~s/\b$word\b//g;

                }
        }

}
print "\n--------OUTPUT---------\n";
print join("\n",@strs);
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is that true
this is from presentation
to create
TO DELETE: [is an to for from]
------PROCESS--------

Words in [is that true] are [is,that,true]
    Deleting [is] from [is that true]
Words in [this is from presentation] are [this,is,from,presentation]
    Deleting [is] from [this is from presentation]
    Deleting [from] from [this  from presentation]
Words in [to create] are [to,create]
    Deleting [to] from [to create]
--------OUTPUT---------
 that true
this   presentation
 create
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Shorter version

@array = qw( is an to  for from);
@strs =("is that true","this is from presentation","to create");
print "\n---- INPUT ----\n";
print join("\n",@strs);

$subs=join("|",@array);

map{s/\b$subs\b//g} @strs;
print"\n---- OUTPUT ----\n";
print join("\n",@strs);
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Perhaps it's just a coincidence, but all the words in your array are stop words. Since you've already been given excellent examples of how to work with your specific variables, here's an option that removes stop words from the strings you've provided--in case that's your primary goal:

use Modern::Perl;
use Lingua::StopWords qw( getStopWords );

my $str  = "is that true";
my $str1 = "this is from presentation";
my $str2 = "to create";

say removeStopWords( eval $_ ) for qw{$str $str1 $str2};

sub removeStopWords {
    my $stopWords = getStopWords('en');
    join ' ', grep { !$stopWords->{$_} } split ' ', $_[0];
}
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Results:

true
presentation
create
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Just include line 2 above in your code, and send a string to removeStopWords and it'll return it sans any stop words.

Hope this helps!

#!/usr/bin/perl 

use autodie;
use strict qw/refs/;
use warnings FATAL => 'all';
use List::AllUtils qw/:all/;

my (@arr) = qw( is an to for from );

my $str1 = ("This is not true");
    print "At least one value is undefined\n"
        if all sub {  
            defined $_ 
        },  @arr;
printf "\t %i item(s) is(are) defined  ", true { defined $_ } $str1;
print "\n";
print  "\t The defined element is: before_incl { defined $_ } @arr";
print "\n";
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You can create a regular expression once and reuse it on each string.

#!/usr/bin/env perl

use strict;
use warnings;

my @del_words = qw{is an to for from};
my $del_words_alt = join q{|} => @del_words;
my $del_re = qr{\b(?>$del_words_alt)\b\s*};

while (<>) {
    s{$del_re}{}g;
    print;
}
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Test run:

$ pm_string_array_del.pl
is that true
that true
this is from presentation
this presentation
to create
create
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