$ xml2yaml
Can't locate YAML.pm in @INC (you may need to install the YAML module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.26.1 /usr/local/share/perl/5.26.1 /usr/lib/x86_64-linux-gnu/perl5/5.26 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.26 /usr/share/perl/5.26 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /usr/bin/xml2yaml line 9.
BEGIN failed--compilation aborted at /usr/bin/xml2yaml line 9.

$ head -n 10 /usr/bin/xml2yaml
#!/usr/bin/env perl

use warnings;
use strict;

use XML::Compile::Schema ();
use XML::Compile::Util   qw/type_of_node/;
use Getopt::Long         qw/GetOptions :config gnu_compat bundling/;
use YAML                 qw/Dump/;

$ sudo apt install libyaml-libyaml-perl
Reading package lists... Done
Building dependency tree       
Reading state information... Done
libyaml-libyaml-perl is already the newest version (0.69+repack-1).
0 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.

Installing /usr/local/man/man3/YAML::Loader::Base.3pm
Appending installation info to /usr/local/lib/x86_64-linux-gnu/perl/5.26.1/perllocal.pod
  TINITA/YAML-1.30.tar.gz
  /usr/bin/make install  -- OK

cpan[2]> q
Terminal does not support GetHistory.
Lockfile removed.
~# 
~# exit
exit
 ~$ xml2yaml
ERROR: no input message specified