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ShellCheck plugin for SonarQube

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In POSIX sh, unary -a in place of -e is undefined.
(or "In dash, ... is not supported." when using dash)
Problematic code
#!/bin/sh
if [ -a file.txt ]
then
  echo "file.txt exists"
fi

Correct code
#!/bin/sh
if [ -e file.txt ]
then
  echo "file.txt exists"
fi

Rationale
-a was used in some shells to check for the existence of a file, but the POSIX standard and better supported equivalent is -e.
Exceptions
If you only intend to target shells that supports this feature, you can change
the shebang to a shell that guarantees support, or [[ignore]] this warning.
You can use # shellcheck disable=SC3000-SC4000 to ignore all such compatibility
warnings.
Related resources

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