Chet Ramey: > On 7/15/19 6:19 PM, astian wrote: > >>> I doubt it makes any difference to the timing, which I think >>> Chet has already answered, but it is worth pointing out that these >>> two commands ... >>> >>> printf '%s\n' "`printf %s "$i"`" >>> printf '%s\n' "$(printf %s "$i")" >>> >>> which (I believe)) are supposed to be the same thing, using the >>> different (ancient, and modern) forms of command substitution aren't >>> actually the same. In the first $i is unquoted, in the second it is >>> quoted. Here, since its value is just a number and IFS isn't being >>> fiddled, there is not likely to be any effect, but if you really >>> want to make those two the same, the first needs to be written as >>> >>> printf '%s\n' "`printf %s \"$i\"`" >>> >>> Such are the joys of `` command substitutions (just avoid them). >>> >>> kre >> >> Dear Robert Elz, I'm aware of several of its peculiarities and I typically do >> avoid them. However, is it true that $i is unquoted in the first case? > > POSIX makes it undefined behavior, and different shells do it differently. > Bash makes the $i quoted within the `` string, as you discovered.
Ah, thanks for the clarification. I wonder if the excerpt below (particularly the last sentence) would be the relevant wording of POSIX, i.e. that some shells might interpret the command as the concatenation of a double-quoted string, the unquoted $i, and another double-quoted string: "`printf %s "$i"`" => CONCAT("`printf %s ", $i, "`") Which would then lead to "undefined results". Cheers. --- 2.2.3 Double-Quotes [0] Enclosing characters in double-quotes ( "" ) shall preserve the literal value of all characters within the double-quotes, with the exception of the characters backquote, <dollar-sign>, and <backslash>, as follows: [...] ` The backquote shall retain its special meaning introducing the other form of command substitution (see Command Substitution). [...] Either of the following cases produces undefined results: - A single-quoted or double-quoted string that begins, but does not end, within the "`...`" sequence - A "`...`" sequence that begins, but does not end, within the same double-quoted string [...] 0: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_03