On Slackware, using
sbopkg permits one to build a package from source. Repos is not big as Debian, but it's nice.
Some software can use environment variables,
for example on the VICE c64 emulator, if the variable
FFMPEG is set to
yes, it will enable
ffmpeg recording the emulator.
I tried to use
$ export FFMPEG=yes; sudo sbopkg -B -i vice
ffmpeg is disabled.
Instead I had to use
$ su - $ export FFMPEG=yes $ sbopkg -B -i vice
How to use environment variables with