SC3016 – ShellCheck Wiki

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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:

#!/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 ] to check if a variable is set can be replaced with [ -n "${variable+x}" ] which uses the "alternative value if set" parameter expansion syntax to accomplish the same thing.

Exceptions:

None

Related resources:

• 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.