print "Number of lines: $nids\n"; print "Content: $ids\n";
How did Perl complain? print $ids should work, though you probably want a newline at the end, either explicitly with print as above or implicitly by using say or -l/$\.
If you want to interpolate a variable in a string and have something immediately after it that would looks like part of the variable but isn’t, enclose the variable name in {}:
print "foo${ids}bar";