On Fri, 9 Feb 2007, Jari Aalto wrote: > FOREWORD > > I have seen following construct to be used in shell-context > (makefiles, sh-scripts, Perl): > > `cmd` [1] > > However, the POSIX standard and SUSv[23] declares alternative way of > accomplishing the same with in *sh context: > > $(cmd) [2]
[..] > All Debian *sh compatible shells support $() and are thus POSIX/SUS > compliant in this respect. [..] > The Single UNIX Specification, Version 2 (SUSv2): > "Shell Command Language" > <http://www.opengroup.org/onlinepubs/007908799/xcu/chap2.html> > > ...The input characters within the quoted string that are > also enclosed between "$(" and the matching ")" will not > be affected by the double-quotes, but rather define that > command whose output replaces the $(...) Your mail makes it sound like $( ) is the only command substitution allowed by POSIX/SUSv[23]. It is not. Let me quote the _really_ relevant section of SUSv2, http://www.opengroup.org/onlinepubs/007908799/xcu/chap2.html#tag_001_006_003 and SUSv3 = POSIX (IEEE1003.1, 2004 Edition), http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_03 Command substitution allows the output of a command to be substituted in place of the command name itself. Command substitution shall occur when the command is enclosed as follows: $(command) or (backquoted version): `command` Further, you didn't yet mention the only disadvantage of backquotes that I personally find important enough to consider, namely that (multi-level) nesting quickly gets horrible. So I personally tend to use $( ) only when nesting. And exactly that is also the only reason mentioned in the Rationale volume of SUSv3/POSIX, http://www.opengroup.org/onlinepubs/009695399/xrat/xcu_chap02.html#tag_02_02_06_03 ... Because of these inconsistent behaviors, the backquoted variety of command substitution is not recommended for new applications __that nest command substitutions or attempt to embed complex scripts__. (my underlining.) Best regards, Anne Bezemer -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
