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

In POSIX sh, string replacement is undefined.

(or "In dash, ... is not supported." when using dash)

Problematic code:

#!/bin/sh
echo "${var//foo/bar}"

Correct code:

Either switch the shebang to bash or ksh, or rewrite the expansion using a tool like sed:

#!/bin/sh
echo "$var" | sed 's/foo/bar/g'

Rationale:

String replacement in parameter expansion is a bash and ksh extension. dash and POSIX sh does not support it.

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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