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The difference between $(command) and `command`

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# 1  
Old 03-08-2007
The difference between $(command) and `command`
In the for loop, we always write like
for CurUser in $( cut -f 1 -d : /etc/passwd )
do
...
done
or
for CurUser in `cut -f 1 -d : /etc/passwd`
do
...
done
Is there any difference between them ?
thanks !
# 2  
Old 03-08-2007
The `backticks` syntax is the old style command substitution which does not allow nesting.
# 3  
Old 03-08-2007
Quote:
Originally Posted by Ygor
The `backticks` syntax is the old style command substitution which does not allow nesting.
It does allow nesting, but the inner backticks must be escaped.
# 4  
Old 03-08-2007
Quote:
Originally Posted by bluepluto
In the for loop, we always write like
for CurUser in $( cut -f 1 -d : /etc/passwd )
do
...
done
or
for CurUser in `cut -f 1 -d : /etc/passwd`
do
...
done
Is there any difference between them ?
thanks !
The backtick version can be used in all Bourne-type shells; the other works in all POSIX shells (ksh, bash, etc.).

It is easier to nest the second version; if you nest backticked substitution, you have to escape the inner backticks.

You should also note that that is almost always the wrong way to read a file (not to mention the useless use of cat):

Code:
while IFS=: read CurUser junk
do
   ...
done < /etc/passwd

# 5  
Old 03-09-2007
Quote:
Originally Posted by cfajohnson
It does allow nesting, but the inner backticks must be escaped.
I was of the notion, nesting of backticks is not possible,

as said escaping the inner backticks worked,

Code:
head `ls -1 \`echo "abhead"  |sed 's/^..//'\``

Thanks! Smilie
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