Frequently Asked Question

What is the difference between $(...) and backticks?

Both forms are command substitution: they run a command and replace the construct with its standard output. today=$(date +%Y-%m-%d) and today=`date +%Y-%m-%d` produce the same result. The dollar-parenthesis form is newer (POSIX, from the late 1980s); backticks are the original Bourne shell syntax, kept for compatibility.

Prefer $( ... )` for two reasons. First, it nests cleanly: `$(echo "$(date)") reads naturally, whereas backticks require escaping inner backticks with backslashes that multiply with each level. Second, the quoting rules inside $() are saner, what you see is what you get, while inside backticks, backslashes have to do double duty for both the backtick parser and the shell. Modern style guides (Google's, the Bash Hackers Wiki, ShellCheck) all recommend $(). Backticks remain valid and you will still see them in older scripts, but write new code in dollar-parens.