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Vidar Holen edited this page Sep 2, 2020 · 1 revision

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:

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

ShellCheck

Each individual ShellCheck warning has its own wiki page like SC1000. Use GitHub Wiki's "Pages" feature above to find a specific one, or see Checks.

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