Linux returns "select: Bad file descriptor" error after using "cat" - linux

Question

I am running a Perl script to read from multiple files on a remote machine. My code looks something like this:
open HANDLE, "/usr/bin/ssh $host cat /home/log_1.log /home/log_2.log 2>>./errorLog.log |"
Basically I am storing the file contents into HANDLE and all errors go into the errorLog.log file. But in my errorLog.log file I keep seeing "select: Bad file descriptor". I am not sure what's causing this and Google searching did not help very much. So my questions are: what does this error mean and how can I resolve it?
EDIT: In the above command, log_2.log may not exist in the remote machine. In that case, I wanted to output the error message into errorLog.log. So when my script finds that the log_2.log file does not exist in the machine, it should log "cat: /home/log_2.log: No such file or directory" but sometimes I see "cat: /home/log_2.log: No such file or directoryselect: Bad file descriptor" (two error messages without a newline).

Answer 1

I see three things wrong with your code:
you aren't checking the return value of open
you are using the two argument version of open
and you are using a bareword filehandle
The first will probably tell you what is going wrong, the other two are not wrong per se, but are not Modern Perl. I would write the code like this
open my $fh, "-|", "/usr/bin/ssh $host cat /home/log_[12].log 2>>./errorLog.log"
or die "could not run remote command: $!";
Or better yet
use IPC::Open3;
use Symbol 'gensym';
my $err = gensym; #deal with stupidity in the IPC::Open3 interface
my $pid = open3 my $in, my $out, $err,
"/usr/bin/ssh", $host, "cat", "/home/log_[12].log";
while (<$out>) {
#do stuff with the stdout of ssh
}
While (<$err>) {
#do stuff with the stderr of ssh
}