A ++ for the proposal using getcwd. An addition:

use strict;
use warnings;
use Cwd qw(getcwd);
use Benchmark qw(:all);


cmpthese(100000, {
    'buildin' => sub {
        my $pwd = getcwd;
    },
    'backtick' => sub {
        my $pwd = `pwd`;
        chomp $pwd;
    },
});
[download]

Output on my computer:

$ perl  am368.pl
            (warning: too few iterations for a reliable count)
              Rate backtick  buildin
backtick    4093/s       --    -100%
buildin  1666667/s   40617%       --
[download]

Backtick operator spawns a subshell. This is expensive. So the rule of thumb should be: Before using backtick for gathering "simple" informations, check whether there is a Perl module providing this information.

Best regards
McA