Free operating system based on the Unix-like GNU on top of the Linux kernel
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${BASH_SOURCE%/*} will get you the directory the currently executing Bash script is in (bash: get the directory this script is in – Jessitron)
Quick and dirty way to seed the disk cache is to just read stuff, e.g. cat ~/org/zettelkasten/*.org >/dev/null. The kernel is pretty aggressive about caching, and won't evict until it needs the memory (tmpfs - Mount /usr in RAM (loading from HDD when starting, and saving to when shutting down) - Ask Ubuntu)