Ok, so here is an example of grepping the output from B::Xref to find out if a particular file contains a sub.

use strict;
use warnings;


my @xref = qx/perl -MO=Xref my_test_file.pl/;

my $subname = "my_sub_name";

my @subs = grep { /(?:\&|Subroutine\s)$subname/ } @xref;

print "$_\n" foreach @subs;
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