Re: Difference between `` and $()
- From: Klaas Vantournhout <no_valid_email@xxxxxxxx>
- Date: Mon, 18 Jun 2007 10:02:03 +0200
Chris F.A. Johnson wrote:
On 2007-06-15, Prateek wrote:
Hi, Can someone please help me understand the difference between
`cat file' and $(cat file) for korn shell. I thought they are teh
same. But my tests show they are not. For example
var=$(cat$(ls)) is different from var=`cat `ls``
var=$(cat $(ls)) is the same as var=`cat \`ls\``
I would refer to bash(1), there they explain the above.
Command Substitution
Command substitution allows the output of a command to replace
the command name. There are two forms:
$(command)
or
‘command‘
Bash performs the expansion by executing command and replacing
the command substitution with the standard output of the command,
with any trailing newlines deleted. Embedded newlines are not deleted,
but they may be removed during word splitting. The command
substitution $(cat file) can be replaced by the equivalent but faster
$(< file).
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by $, ‘, or
\. The first backquote not preceded by a backslash terminates the
command substitution. When using the $(command) form, all characters
between the parentheses make up the command; none are treated
specially. Command substitutions may be nested. To nest when using the
backquoted form, escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting and
pathname expansion are not performed on the results.
regards
Klaas
.
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