diff --git a/SC3031.md b/SC3031.md new file mode 100644 index 0000000..b1be79e --- /dev/null +++ b/SC3031.md @@ -0,0 +1,39 @@ +## In POSIX sh, redirecting from/to globs is undefined. + +(or "In dash, ... is not supported." when using `dash`) + +### Problematic code: + +```sh +#!/bin/sh +date > /tmp/log*.txt +``` + +### Correct code: + +To redirect from/to the only match of a glob, expand the glob first: + +```sh +#!/bin/sh +set -- /tmp/log*.txt +# PS: This is a good place to verify that there was exactly one match +date > "$1" +``` + +Alternatively, use a loop to redirect from/to all if that was the intention. + +### Rationale: + +Shells differ in whether (and how) they do pathname expansion on names in redirections. Avoid the issue by expanding the glob yourself. + +### 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!