[ANSWER AT THE END OF THIS POST]
I just installed the php5-cli package in Ubuntu 11.04. If I run:
/usr/bin/php5 -a # The -a is for interactive mode
I get the output:
Could not startup.. However, if I add the
-n option, which makes it ignore the php.ini file, everything works fine. The php.ini file is basically the default one, with some minor changes (memory limit, error reporting level, etc.).
ANSWER (I can't post an answer to my own post yet):
Well, turns out php-cli wasn't finding the php.ini file (and for some reason didn't told me so :). Specifying it with the -c option did the trick.