nixpkgs/pkgs/tools/graphics/gnuplot/set-gdfontpath-from-fontconfig.sh
Andreas Herrmann 79e145a970 gnuplot: Improve startup performance
Before executing the gnuplot executable the environment variable `GDFONTPATH`
is populated with a list of font directories, which is obtained from `fc-list`.
In that process we iterated over each line and called `dirname` on it, which
introduces a performance hit for loading and executing the external executable
`dirname` every time.

The new version avoids the loop.

The author of this patch measured a 42 fold performance improvement:

old version:

    $ time ./gnuplot_old/bin/gnuplot -e ''
    real    0m3.828s
    user    0m0.392s
    sys     0m0.465s

new version:

    $ time ./gnuplot_new2/bin/gnuplot -e ''
    real    0m0.091s
    user    0m0.112s
    sys     0m0.014s

The correctness of the value of `GDFONTPATH` was confirmed with the following
command and comparing its output between versions:

    $ gnuplot -e 'print system("echo $GDFONTPATH")'
2016-01-11 15:37:07 +01:00

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p=( $(fc-list : file | sed "s@/[^/]*: @@" | sort -u) )
IFS=:
export GDFONTPATH="${GDFONTPATH}${GDFONTPATH:+:}${p[*]}"
unset IFS p