SC3016 – ShellCheck Wiki

In POSIX sh, unary `-v` (in place of `[ -n "${var+x}" ]`) is undefined.

Problematic code:

#!/bin/sh
if [ -v STY ]
then
  echo "STY is set, you are using screen"
fi

Correct code:

Either switch to bash or ksh, or use:

#!/bin/sh
if [ -n "${STY+x}" ]
then
  echo "STY is set, you are using screen"
fi

Rationale:

Your script uses a shell feature not supported by the shebang. Either rewrite the script to be portable, or change the shebang to explicitly require a shell like Bash.

In this case, [ -v variable ], which checks if a variable is set, is not specified by POSIX. It can be replaced with the portable [ -n "${variable+x}" ], which uses the "alternative value if set" parameter expansion syntax to accomplish the same thing.

Exceptions:

None

Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!

ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.