You could use a regex to either match the characters that you want or alternatively to not match the characters that you don't want:

    #!/usr/bin/perl -wl

    use strict;

    my $scalar = '1335';

    print "Found" if  $scalar =~ /^[1-5]+$/;
    print "Found" if  $scalar !~ /[^1-5]/;
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--
John.