UNIX for Advanced & Expert Users

$ echo $date

$ echo $(date)
Tue Aug 16 03:10:25 EDT 2011

% echo $date

% date=qwerty

% echo $date
qwerty

% date
Tue Aug 16 14:25:38

% echo `date`
Tue Aug 16 14:25:53

% echo $(date)
Tue Aug 16 14:25:58

% echo $(whoami)
yazu

# Using $():
[root@atlas]# a=$(date)
[root@atlas]# echo $a
Tue Aug 16 09:35:38 CDT 2011

# Produces the same as ``
[root@atlas]# a=`date`
[root@atlas]# echo $a
Tue Aug 16 09:35:51 CDT 2011

# Nested $() looks clean and it's easy to read:
[root@atlas]# a=$(date $(echo "-u" $(echo "+%T")))
[root@atlas]# echo $a
14:41:48

# Whereas nested `` looks weird and sloppy:
[root@atlas]# a=`date \`echo "-u" \\\`echo "+%T"\\\`\``
[root@atlas]# echo $a
14:42:09

$ echo `echo hello`
hello
$ echo `echo hello  `echo there``  #  Trouble nesting
helloecho there
$ echo `echo hello  \`echo there\``  # Getting ugly
hello there
$ echo $(echo Hello $(echo there))  # Handles nesting
Hello there
$