I do not know how to correctly find the system font files on linux.

From what I have learned, my current algorith is this:
1. read the /etc/fonts/fonts.conf
note all direcotry paths from <dir></dir> elements

example:
I note /usr/share/fonts fonts <dir>/usr/share/fonts</dir>

2. use fc-match to match a font family. get the font file name from the output from fc-match. search inside the directories from (1) for that font file.

example:
fc-match arial
n019003l.pfb: "Nimbus Sans L" "Regular"

find /usr/share/fonts/ -name n019003l.pfb
/usr/share/fonts/default/Type1/n019003l.pfb

//------

Is this approach for finding fonts portable? Can I use this on Ubuntu, Centos, Debian etc.?
Is fc-match itself portable?

Thanks

found out that if I run fc-match verbouse it gives me the file path. So step 1 is no longer needed.

example:
fc-match -v "Times":bold:italic
Pattern has 25 elts (size 32)
family: "Nimbus Roman No9 L"(s)
style: "Bold Italic"(s)
slant: 100(i)(s)
weight: 200(i)(s)
width: 100(i)(s)
size: 12(f)(s)
pixelsize: 12.5(f)(s)
foundry: "urw"(s)
hintstyle: 3(i)(s)
hinting: FcTrue(s)
verticallayout: FcFalse(s)
autohint: FcFalse(s)
globaladvance: FcTrue(s)
file: "/usr/share/fonts/default/Type1/n021024l.pfb"(s)
...

tested fc-match on Ubuntu, Suse, Centos.
fc-match -v output is consitant on all these platforms.

It remains to find a modern distro where fc-match does not work.