I don't see anywhere where you are setting $_. If (as it appears) $_ is undef, then it won't match your regex and the while loop won't ever execute..

Further to davorq's most apposite observation, even if $_ had been defined, the $_ =~ is redundant since $_ =~ /RE/ and /RE/ are exactly equivalent.

You might also want to use the standard strictures and warnings.

I'm guessing something like this might be a little closer to what you want (to check that, for each tag in a list of tags, the tag body can be found in a named array of valid tag names - or some such) ...

use strict;
use warnings;
.
.
sub validate_tag {
    # Assume tags passed as arg list
    while("@_" =~ /<(.+?)>/g) {
        print "Invalid tag $1 found" unless grep /(:?$1)/, @{$ARGV[1]}
+;
    }
}
.
.
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A user level that continues to overstate my experience :-))

$ gash.pl dummy jim
Global symbol "@arr1" requires explicit package name
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use strict;
use warnings;

our @fred = qw(The quick brown camel);
our @jim  = qw(Fee Fie Foe Fum);

sub validate_tag
{
    my $arr1;
    my $cmd =  "\$arr1 = \\\@$ARGV[1]";
    eval $cmd;
    print "$arr1->[0]\n";
}

validate_tag();
# end of script

$ gash.pl dummy jim
Fee
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If $arr1 holds the name of the array, you can step through the array with

foreach my $x (0..$#{$arr1})
{
  if($arr1->[$x] eq $1){$found++}
}
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IMO loops like this are better written as

foreach my $x (@$arr1)
{
  if ($x eq $1) {$found++}
}
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You might read up on references and their use in References

No; $#arr1 is returning the correct number of elements in the array; it's just not returning the number of elements you expect to be in the array. Where do you populate @arr1?

Don't think so. My interpretation of his code and his question is that he wants to use symbolic references: See "I have several arrays in my script" and "with $ARGV[1] as the array *name*". So in $arr1 is the name of the real array and he wants to access that.

You're quite likely correct; it's just that from the code fragment given by the OP, I couldn't find where his array was being populated. I also tend to think that an event like $#arr1 giving an incorrect value is unlikely; I would expect that $#arr1 is among the Perl features least likely to have any bugginess. My thinking (I'm easily confused by symbolic references, so I'm likely wrong) is that $#arr1 isn't quite the same as scalar(@$arr1)-1.

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