Question

When I found Perl’s $^O, I was curious whether there are more variables like this, because ^ reminded me of a regular expression. When I enter

print "$(^b)";

it comes up with some numbers:

1000 81 90 91 92 93 100 150 1000

What to these mean? Is this some kind of 0xdeadbeef?

Answer 1

I think you are just printing out the value of $(.

The real gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated list of groups you are in. The first number is the one returned by getgid() , and the subsequent ones by getgroups() , one of which may be the same as the first number.

However, a value assigned to $( must be a single number used to set the real gid. So the value given by $( should not be assigned back to $( without being forced numeric, such as by adding zero. Note that this is different to the effective gid ($) ) which does take a list.

You can change both the real gid and the effective gid at the same time by using POSIX::setgid() . Changes to $( require a check to $! to detect any possible errors after an attempted change.

Here is the comparison:

diff <(perl -le 'print "$(";') <(perl -le 'print "$(^b)";')
1c1
< 20 20 402 12 33 61 79 80 81 98 100 204 401
---
> 20 20 402 12 33 61 79 80 81 98 100 204 401^b)