uiop
UIOP, the Utilities for Implementation- and OS- Portability, is a portability layer and basic utility library that comes as part of ASDF 3.

UIOP is a generalization and robustification of portability features previously found in ASDF 2, xcvb, trivial-backtrace, cl-launch, cl-fad, and more.

Notable exported symbols (functions, variables, macros) include: subpathname, run-program, getenv, getenv-pathname, call-function, parse-native-namestring, getcwd, chdir, register-image-restore-hook, *command-line-arguments*, *uninteresting-conditions*, define-package, with-temporary-file, with-output, if-let, uiop-debug.

See the README file for a guide.

Browse the source for more functions with appropriate docstrings or comments.