Frequently Asked Question

What is the difference between single quotes, double quotes, and backticks?

Single quotes '…' are the most literal: every character between them, including $`, `\`, and backticks, is taken at face value. `echo '$HOME' prints exactly $HOME. Use single quotes when you want the shell to keep its hands off the contents, file names with spaces, regular expressions, fixed strings.

Double quotes "…" are softer: they preserve whitespace and most punctuation but still allow three expansions, variable expansion ($var), command substitution ($(cmd)`), and arithmetic expansion (`$((1+1))). echo "Home is $HOME" prints Home is /home/chris. Use double quotes for strings that should be treated as a single argument but where you do want variables to interpolate.

Backticks `…` are an old form of command substitution, equivalent to $() but harder to nest and read. They're not a quoting form in the same sense as the other two; modern code should use $() instead. The general rule with quoting is: quote everything that holds a value ("$var"`, not `$var) so that whitespace and glob characters in the value don't break your command.