=word}
If varname exists and isn't null, return its value; otherwise set it to word and then return its value.[7]
Purpose:
Setting a variable to a de... IPT_FUNCTION, if it exists, with no arguments; if its return value is non-zero: exits the script with the same code. The default value is main.
Exits the script with the return code of the action fun... functions that may be used to build test suites; its aim is at building tests for bash functions/comma
