What does +x mean in Bash scripting? [duplicate]

Question

What does +x mean in the below statement?

if[ -z ${FSV_ROOT+x} ]

Answer 1

Read up on Use Alternative Value. See 2.6.2 Parameter Expansion.

In parameter expansion, if a parameter is unset or null, null shall be substituted; otherwise, the expansion of word shall be substituted. Use of the colon in the format shall result in a test for a parameter that is unset or null; omission of the colon shall result in a test for a parameter that is only unset.

So in your case:

If FSV_ROOT is set and not null, substitute x

If FSV_ROOT set but null, substitute x

If FSV_ROOT is unset, substitute null