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You may have to disable fortran and openmp using the USE variable too. YMMV.
This works in combination with http://www.commandlinefu.com/commands/view/10496/identify-exported-sonames-in-a-path as it reports the NEEDED entries present in the files within a given path. You can then compare it with the libraries that are exported to make sure that, when cross-building a firmware image, you're not bringing in dependencies from the build host.
The short version of it as can be seen in the same output is
scanelf -RBnq -F "+n#f" $1 | tr ',' '\n' | sort -u
This provides a list of shared object names (sonames) that are exported by a given tree. This is usually useful to make sure that a given required dependency (NEEDED entry) is present in a firmware image tree.
The shorter (usable) version for it would be
scanelf -RBSq -F "+S#f"
But I used the verbose parameters in the command above, for explanation.
Use bc for decimals...
enable each bash completion that you have installed at your system, that's very nice ;)
The command requires app-text/xmlstarlet but it otherwise self-contained. It extracts all the herds and all the maintainers' email for a given package and is what I'm using on the Tinderbox to make it easier for me to report bugs.
Problem arises when ebuild gets removed from portage and you end up with old and unmaintained package that you cannot find standard way. This oneliner will give you list of those packages.
The output is only partial because runtime dependencies should count in also commands executed via system() and libraries loaded with dlopen(), but at least it gives an idea of what a package directly links to.
Note: this is meaningful *only* if you're using -Wl,--as-needed in your LDFLAGS, otherwise it'll bring you a bunch of false positives.
Revised approach to and3k's version, using pipes and read rather than command substitution. This does not require fiddling with IFS when paths have whitespace, and does not risk hitting command-line size limits.
It's less verbose on the missing files, but it stops iterating at the first file that's missing, so it should be definitely faster.
I expanded all the qlist options to be more self-describing.
This loops through all installed ebuilds and checks if every file that should be installed is still there and if not adds it to emerge. It includes a verbose output to stderr too.
If you have packages installed that have whitespace in their filenames you have to change the IFS to "newline".
Whenever you compile a new kernel, there are always new modules. The best way to make sure you have the correct modules loaded when you boot is to add all your modules in the modules.autoload file (they will be commented) and uncomment all those modules you need.
Also a good way to keep track of the available modules in your system.
For other distros you may have to change the name of the file to /etc/modprobe.conf
On a Gentoo system, this command will tell you which packets you have installed and sort them by how much space they consume. Good for finding out space-hogs when tidying up disk space.
If you do not use this command, portage will fetch the source again, and rebuild the hole application from the top.
This command make portage keep all files that ar allready built
This command puts all the flags of the USE variable actually used by the packages you emerged to the file "use", and those which are unused but available to the file "notuse"