What's the difference between $(stuff) and `stuff`?

There are two syntaxes for command substitution: with dollar-parentheses and with backticks. Running top -p $(pidof init) and top -p `pidof init` gives the same output. Are these two ways of doing the same thing, or are there differences?


ANSWER:-


The old-style backquotes ` ` do treat backslashes and nesting a bit different. The new-style $() interprets everything in between ( ) as a command.

echo $(uname | $(echo cat))
Linux

echo `uname | `echo cat``
bash: command substitution: line 2: syntax error: unexpected end of file
echo cat

works if the nested backquotes are escaped:

echo `uname | \`echo cat\``
Linux

backslash fun:

echo $(echo '\\')
\\

echo `echo '\\'`
\

The new-style $() applies to all POSIX-conformant shells.
As mouviciel pointed out, old-style ` ` might be necessary for older shells.
Apart from the technical point of view, the old-style ` ` has also a visual disadvantage:

• Hard to notice: I like $(program) better than `program`
• Easily confused with a single quote: '`'`''`''`'`''`'
• Not so easy to type (maybe not even on the standard layout of the keyboard)