if ((-e "1\.txt")||(-e "2\.txt")){
        $file_name=$_;
        $fh->new IO::File "<$file_name" or die $!;
}

my $file_name;
if ( -e "1.txt"){
        $file_name=$_;
}
elsif( -e "2.txt" ){
    $file_name = $_;
}

if( $file_name ){
    $fh =  IO::File "<$file_name" or die $!
}

my $file_name;
if (-e ($file_name = "1\.txt") or -e ($file_name = "2\.txt")){
    $fh->new IO::File "<$file_name" or die $!;
}