Environment Variables

Gnucash obeys different specific environment variables, which can be set before the program start:

Name     Meaning
GNC_HOME
GNC_BIN
GNC_LIB
GNC_DATA
GNC_CONF
SYS_LIB

Source: environment_override in gnucash-bin.c

There are also System wide variables which affect Gnucash like Locale Settings.

A more comprehensive list, using grep -r --include=*.c getenv src:

GNC_ACCOUNT_PATH: src/backend/xml/test/test-load-example-account.c
GNC_AUTO_SCRUB_LOTS:
   src/engine/Transaction.c
   src/gnome/gnc-plugin-page-account-tree.c
GNC_DBD_DIR: src/backend/dbi/gnc-backend-dbi.c
GNC_DEFAULT_DATABASE: src/gnome-utils/dialog-file-access.c
GNC_DOT_DIR: src/core-utils/gnc-filepath-utils.c
GNC_GCONF_PATH: src/bin/gnucash-bin.c
GNC_MODULE_PATH: src/gnc-module/gnc-module.c
GNC_TEST_FILES: 
   src/backend/xml/test/test-load-xml2.c
   src/backend/xml/test/test-xml2-is-file.c
   src/import-export/qif/test/test-qif.c 

CONTENT_LENGTH:
   src/experimental/cgi-bin/hello3.c
   src/experimental/cgi-bin/gnc-server.c
   src/experimental/cgi-bin/fastcgi-hello.c
HTTP_COOKIE: src/experimental/cgi-bin/gnc-server.c
HTTP_USER_AGENT: src/experimental/cgi-bin/gnc-server.c
QUERY_STRING: src/experimental/cgi-bin/fastcgi-hello.c
REQUEST_METHOD:
   src/experimental/cgi-bin/fastcgi-hello.c
   src/experimental/cgi-bin/gnc-server.c
   src/experimental/cgi-bin/hello3.c
SERVER_NAME: src/experimental/cgi-bin/fastcgi-hello.c

GWEN_LOGLEVEL: src/import-export/aqbanking/gnc-ab-utils.c
AQBANKING_LOGLEVEL: src/import-export/aqbanking/gnc-ab-utils.c

PATHEXT: src/bin/gnucash-bin.c
SRCDIR: src/backend/xml/test/test-load-xml2.c