You are confusing two different mechanisms here.

2>&1 is a shell directive, it is nothing to do with Perl. It means: "redirect file descriptor 2 to file descriptor 1". The & indicates a file descriptor rather than a file called "1". File descriptors are indexes to a process's open files and point to kernel's internal tables. 0 (zero) is STDIN, 1 is STDOUT and 2 is STDERR. This is the case on UNIX/Linux systems and on Windows console programs. Shells like the Korn shell (ksh), Bash, and Bourne shell (sh) support this notation, and even cmd.exe and Powershell on Windows. C shell (csh or tcsh) does not, it requires a different syntax.

As others have said, `backticks` or qx capture STDOUT, which is this case includes STDERR output, however you are not capturing it. Usually you would do something like this:

use strict;
use warnings;
my $capture = `ifconfig 2>&1`;
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This enables us to inspect the output (in $capture in this case. If you want the output displayed on the screen then use system instead. If you want both then just print $capture