Command Substitution (zsh)

### 14.4 Command Substitution ¶

A command enclosed in parentheses preceded by a dollar sign, like ‘`$(`...`)`’, or quoted with grave accents, like ‘```...```’, is replaced with its standard output, with any trailing newlines deleted. If the substitution is not enclosed in double quotes, the output is broken into words using the `IFS` parameter.

The substitution ‘`$(cat` foo`)`’ may be replaced by the faster ‘`$(<`foo`)`’. In this case foo undergoes single word shell expansions (parameter expansion, command substitution and arithmetic expansion), but not filename generation.

If the option `GLOB_SUBST` is set, the result of any unquoted command substitution, including the special form just mentioned, is eligible for filename generation.