Find dependencies

Some ports' Makefiles contain line-continuations making it non-trivial to find dependencies etc. These lines end in a '\' so an OPT_USE could be on one line whereas the mysql may appear on a different line

To counter this, use

perl -pe 's/\\\n/ /' {} \;

to remove line-continuations.

Finding in (all) files is a lot easier with textproc/the_silver_searcher. To find all relevant files containing references to mysql as a first filter use

ag --ignore 'pkg-*' --ignore 'distinfo' --ignore 'patch-*' mysql

Silver Searcher will perform a case-insensitive search by default

This example is used to refactor the MySQL part from Mk/bsd.databases.mk to Mk/Uses/mysql.mk

To find all files requiring MySQL, you could use something like

for file in `ag --ignore 'pkg-*' --ignore 'distinfo' --ignore 'patch-*' -l mysql` ; do
   perl -pe 's/\\\n/ /' $file \
     | grep -iE '(USE_MYSQL|_USE.*mysql)' \
     | sed -ne "/[Mm][Yy][Ss][Qq][Ll]/s|^|${file}:|p"
done

Breaking this down

1. Fast finding in files, limits the number of files that we need to process and many forks
2. Concatenate continued lines so we can use grep
3. Depenencies come in two forms that we need to find (USE_MYSQL and OPT_USE are always caps but the latter allows for mixed case values) - USE_MYSQL= boolean:option - OPT_USE= mysql=option
4. We want to know what file this appears in, so add it again using sed