# Environment variables

Hy treats the following environment variables specially. Boolean environment variables are interpreted as false when set to the empty string and true when set to anything else.

HYSTARTUP

  (Default: nothing) Path to a file containing Hy source code to execute when starting the REPL.

HY_SHOW_INTERNAL_ERRORS

  (Default: false) Whether to show some parts of tracebacks that point to internal Hy code and won't be helpful to the typical Hy user.

HY_HISTORY

  (Default: `~/.hy-history`) Path to which REPL input history will be saved.

HY_MESSAGE_WHEN_COMPILING

  (Default: false) Whether to print "Compiling FILENAME" to standard error before compiling each file of Hy source code. This is helpful for debugging whether files are being loaded from bytecode or re-compiled.