diff --git a/SC3050.md b/SC3050.md new file mode 100644 index 0000000..92bfdf1 --- /dev/null +++ b/SC3050.md @@ -0,0 +1,32 @@ +## In POSIX sh, `printf %q` is undefined. + +(or "In dash, ... is not supported." when using `dash`) + +### Problematic code: + +```sh +ssh host "cat $(printf "%q" "$remotefile")" +``` + +### Correct code: + +There is not really a good, built-in way to escape a string for a remote shell in POSIX sh. However, you can replace each `'` in the input with `'\''` and then wrap the whole results in single quotes: + +```sh +escape() { printf "'%s'\\n" "$(printf '%s' "$1" | sed -e "s/'/'\\\\''/g")"; } +ssh host "cat $(escape "$remotefile")" +``` + +Alternatively, switch to a shell that *does* support `printf %q` like `ksh` or `bash`. + +### Rationale: + +`printf %q` is a bash and ksh extension. It's not supported on POSIX sh or dash. + +### Exceptions: + +If the command is gated by a check for the correct shell, you can [[ignore]] this warning. + +### Related resources: + +* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!