Environment: OSX, AMMPS
Maybe caused by the particular version of PHP shipped with AMMPS and symlinked by default (PHP 5.3.21 at this time).
For example this command:
/Applications/AMPPS/php/bin/php ~/wp-cli.phar --info
Prints:
???p?
To fix it, update AMMPS to the latest. This includes PHP 5.4.11, but does not link it as the default.
Now this command:
/Applications/AMPPS/php-5.4/bin/php ~/wp-cli.phar --info
Prints:
PHP binary: /Applications/AMPPS/php-5.4/bin/php-5.4.11
PHP version: 5.4.11
php.ini used:
WP-CLI root dir: phar://wp-cli.phar
WP-CLI global config:
WP-CLI project config:
WP-CLI version: 0.15.0
Now fix it more permanently by adding that version to your PATH, i.e.
export PATH="/Applications/AMPPS/php-5.4/bin/:/Applications/AMPPS/mysql/bin:$PATH"