2 SC3016

Lawrence Velázquez edited this page 2024-03-08 19:43:55 -05:00

Table of Contents

• In POSIX sh, unary -v (in place of [ -n "${var+x}" ]) is undefined.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:
• Related resources:

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

Related resources:

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

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