Ho to check gems ready to update, without update them?
If you are not using bundler, just run gem outdated and it will give you a list of outdated gems.
Example of output:
$ gem outdated
acts_as_tree (2.7.1 < 2.9.1)
addressable (2.4.0 < 2.7.0)
bcrypt (3.1.12 < 3.1.13)
bootsnap (1.4.5 < 1.4.6)
bootstrap (4.3.1 < 4.4.1)
brakeman (4.7.2 < 4.8.0)
cancancan (1.17.0 < 3.0.2)
chart_js (1.1.0 < 1.1.1)
coffee-rails (4.2.2 < 5.0.0)
combustion (0.6.0 < 1.1.2)
database_cleaner (1.8.2 < 1.8.3)
...