# for sub cleaner { my $var = shift; $var =~ s/foo/bar/; $var }
my $var = cleaner($var);
# then maybe lines later...
print $var
# or in a single line
print cleaner($var);

# or this if you have sub cleaner { $_[0] =~ s/foo/bar/ }
cleaner($var);
# then maybe lines later...
print $var;
# and you can't
print cleaner($var)
# unless you have sub cleaner { $_[0] =~ s/foo/bar; $_[0] }