Compress::Zlib is reasonably common... it is even used by
CPAN when installing new modules, if it is available. If you cannot use (or don't want to use) command line tools, i suggest
Compress::Zlib as the best alternative.
On the pure-perl-command-line front, i would think that the Perl Power Tools people would be the best to check ... tho i don't believe gzip is on their list.
$ perl -e 'do() || ! do() ;'
Undefined subroutine &main::try