[[ $VAR ]] appears to be equivalent to [[ -n $VAR ]]
The bash manual says:
which implies an operator is required, but it's not.
Is the bash double bracket conditional expression without operators, specified/documented anywhere?
Viewed 38
1 Answers
They're listed as equivalent in the Conditional Expressions section of the bash man page:
string
-n string
True if the length of string is non-zero.
This is also implied by the POSIX spec for the test command (which is equivalent to [ ], which the [[ ]] syntax is based on):
In the following list, $1, $2, $3, and $4 represent the arguments presented to test:
0 arguments:
Exit false (1).
1 argument:
Exit true (0) if $1 is not null; otherwise, exit false.
Therefore [ ] and [ '' ] exit with false/failure status, but [ something_nonblank ] exits with true/success status.
Related