Assertion: parameter | /r/HasProperty | unset
Facets:
Source sentences:
text: , Bash tests for a parameter that is unset or null.
text: Omitting the colon results in a test only for a parameter that is unset.
text: If parameter is unset or null, the expansion of word is substituted.
text: If parameter is unset or null, the expansion of word is assigned to parameter .
text: If parameter is null or unset, the expansion of word (or a message to that effect if word is not present) is written to the standard error and the shell, if it is not interactive, exits.
text: If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substituted.