Diff for "BashFAQ/082"

Differences between revisions 3 and 4

Why is $(...) preferred over `...` (backticks)?

For several reasons:

It makes nesting command substitutions easier. Compare:
- ```
  x=$(grep $(dirname "$path") file)
  x=`grep \`dirname "$path"\` file`
```
It just gets uglier and uglier after two levels.
It's easier to read.
Newbies who see $() don't normally press the wrong keys. On the other hand, newbies who see `cmd` often mangle it into 'cmd' because they don't know what a backtick is.

Backslashes (\) inside backticks are handled in a non-obvious manner:

  echo "`echo \\a`"      # prints a
  echo "`echo \\\a`"     # prints \a
  echo "`echo \\\\a`"    # prints \a

Inside $(), there are no such surprises.

Backslashes are no more no less surprising than elsewhere IMHO

  echo `echo \a` # prints a
  echo `echo \\a` # prints a
  echo `echo \\\a` # prints \a
  echo `echo \\\\a` # prints \a
  echo $(echo \a)  #prints a
  echo $(echo \\a) prints \a
  echo $(echo \\\a) prints \a
  echo $(echo \\\\a) prints \\a

the same sort of things happens without any quotes or within "".

I suspect the real advantage of $( ) here is that you don't need to take extra care of the quotes (\ ""), you just put them as usual, ie echo "echo \"foo bar\"" vs echo "$( echo "foo bar")" -- pgas

The only time backticks are preferred is when writing code for the oldest Bourne shells, which do not know about $().

-  ⇤ ← Revision 3 as of 2007-09-13 19:19:33 → 
  Size: 895
  Editor: BetterWorld
  Comment: Add example for non-obvious backslashing behaviour
+   ← Revision 4 as of 2007-09-14 11:52:14 → ⇥
  Size: 1499
  Editor: leon
  Comment: are they really surprising? maybe we can generalize to all quotes instead?
-Deletions are marked like this.
+Additions are marked like this.
 Line 25:
+Backslashes are no more no less surprising than elsewhere IMHO
{{{
  echo `echo \a` # prints a
  echo `echo \\a` # prints a
  echo `echo \\\a` # prints \a
  echo `echo \\\\a` # prints \a
  echo $(echo \a)  #prints a
  echo $(echo \\a) prints \a
  echo $(echo \\\a) prints \a
  echo $(echo \\\\a) prints \\a
}}}
the same sort of things happens without any quotes or within "".

I suspect the real advantage of $( ) here is that you don't need to take extra care of the quotes (\ ""), you just put them as usual, ie
echo "`echo \"foo    bar\"`" vs echo "$( echo "foo     bar")"  -- pgas