#!perl -w
use strict;

my $key="5	10	14	16	17	20	25	26	38  1  42	47	54";
my $substr = " 1 ";
my @newarray= $key;
foreach $key ( @newarray ) {
    if (index($key, $substr) != -1) {
        print "\nExist (substr)"
    };
    if ($key =~ /\Q$substr\E/) {
        print "\nExist (RE)"
    };
    if ($key =~ /\s+1\s+/) {
        print "\nExist (whitespace)"
    };
}
__END__

>perl -w tmp.pl

Exist (substr)
Exist (RE)
Exist (whitespace)