The emerge command / tool is the heart of the Gentoo Linux package management system known as Portage. The command is fairly complex with many options and modifiers. It is written in python. emerge is the most important utility to access the features of Portage from the command line.
The program will download the source code of a specified application, as well as all other applications or libraries needed to satisfy dependencies. Once downloaded, everything is compiled from source. The compilation settings can be optimised, based on the specifications of the individual computer, and on the individual user's need for speed. The emerge utility will compile and install the applications in a sandbox environment. This way any applications in use are protected right up to the point when the new software is (e)merged into the Gentoo Linux system.
What emerge installs as dependencies is affected by the USE flag -settings. They decide which optional features will be included when installing or upgrading an application. emerge can also be used to download and install binary files, although this is not taking full advantage of Gentoo Linux.
Some of the major commands for emerge are:
# emerge package-name
This will install package-name and all its dependencies.
# emerge --pretend package-name
This will cause emerge to list all of the programs it will install as dependencies to program-name, but will not actually install anything.
A major disadvantage of emerge is that it does not remove no longer needed dependencies when a certain package is uninstalled. However, using the command:
# emerge depclean
one can clean the unused dependencies.
emerge can also be used to remove multiple version of the same applications / dependencies (which is handled by "slots" in Portage). It is used in this way:
# emerge -P package-name
To query what multiple version of the same applications / dependencies can be removed, the following command should be issued:
# emerge -pP
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