use strict;
use warnings;

use Data::Dumper;

sub findLines {
    open(my $error_fh, '<', 'iset_error_log') or die($!);
    my @lines;
    while((my $line = <$error_fh>)) {
  
        next unless($line =~ /\[notice/); skipp all lines except notice

        # yada, do something to $line

        push @lines, $line;
    }

    close($error_fh);
    return @lines;
}

my @found = findLines();
print Dumper(\@found);