Using telnet with pipe with backticks in perl

问题:

I am trying to test a specific server is up and running on a certain port so I am using $result = `echo exit | telnet 127.0.0.1 9443`; print $result;

Here I am using localhost for privacy issues The expected behavior is that it should print "...Could not open connection to the host, on port 9443: Connect failed", this way I know that the server is not running. but it prints an empty string

Any help on this

回答1:

The failure message is printed to STDERR, while backticks return only what goes to STDOUT.

You can redirect the STDERR stream to the STDOUT stream

$result = `echo exit | telnet 127.0.0.1 9443 2>&1`; 

See I/O redirection.

---

There are more rounded ways to do this, using various forms of open. See it in perlfaq8. There are also various modules for this. The Capture::Tiny makes it rather easy.

use warnings 'all';
use strict;

use Capture::Tiny qw(capture);

my $cmd = 'echo exit | telnet 127.0.0.1 9443';

my ($stdout, $stderr) = capture {
  system ( $cmd );
};

print "STDOUT: $stdout";
print "STDERR: $stderr";

This prints for me

STDOUT: Trying 127.0.0.1...
STDERR: telnet: connect to address 127.0.0.1: Connection refused

The module has many more capabilities. From the docs

Capture::Tiny provides a simple, portable way to capture almost anything sent to STDOUT or STDERR, regardless of whether it comes from Perl, from XS code or from an external program.