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Full Discussion: [Discussion] POSIX, the Love of Backticks and All That Jazz
Top Forums UNIX for Advanced & Expert Users [Discussion] POSIX, the Love of Backticks and All That Jazz Post 302990550 by Scrutinizer on Saturday 28th of January 2017 07:43:46 AM
Old 01-28-2017
Quote:
Originally Posted by Don Cragun
Hi Peasant,
You are correct in saying that back-quotes are not deprecated as a method of performing command substitution in the standards. And, even though some people would like to, it is unlikely that the standards will formally deprecate back-quoted command substitution because so many existing (otherwise strictly conforming) shell scripts use them.

But, when writing new scripts (unless you intend to have them run on a pure Bourne shell that doesn't have $(command) command substitution), I would always suggest using the $(command) form... Note that:
  1. $(command) command substitutions can be nested,
  2. `command` command substitutions cannot be nested, and
  3. if you need to quote the results of a command substitution where the command contains a double-quoted string, the double quotes inside a $(command) command substitution are not affected by double quotes outside the command substitution; but double quotes inside a `command` command substitution produce undefined results if the command substitution is inside double quotes.
Hi Don, `command` command substitutions can be nested, but the inner backquotes need to be escaped..
Code:
$ echo "$(echo "foo  $(echo "bar  baz")")" 
foo  bar  baz
$ echo "`echo \"foo  \`echo \\\"bar  baz\\\"\`\"`" 
foo  bar  baz

Also, IMO double quotes inside a `command` command substitution do not produce undefined results; they need to be properly escaped in accordance to the nesting level, which quickly leads to an escape hell, but it is not impossible. Why anyone would prefer backticks over $( ... ) is beyond me though..
Last edited by Scrutinizer; 01-28-2017 at 11:26 AM..
This User Gave Thanks to Scrutinizer For This Post:
RavinderSingh13
 

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