I'm trying to get a check that tests the first letter or the full word of parameters and it is failing (or succeeding I suppose). 
use strict;
use warnings;

use Pod::Usage;

my $format = {
    abc => 1,
    bar => 1,
    fii => 1,
    wee => 1,
};

my $opts;
$opts->{params} = ["a", "b"];

if (!grep { /^(join('|', $opts->{params}))/i } keys %$format)
{
  pod2usage( -verbose => 0, -output => \*STDERR,
          -msg => "$0 bad parameter difinition used [" . join(", ", so
+rt {$a cmp $b} @{$opts->{params}}) . "].\n" .
                  "Possible parameters are: " . 
                  join(", ", sort {$a cmp $b} keys %$format) . "\n");
}

print "1\n";

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EDIT: It seems I haven't defined what should succeed and fail - it should match the first characters in a string. So, In the above example with parameters: abc, bar, fii, and wee,
a should succeed
b should succeed
ac should fail
aB should succeed
fA should fail
ee should fail

In reply to check parameters by ag4ve

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