How to use the bash builtin to replace the output of a subshell or function

No, that nesting of substitution operators is unique to zsh.

Note that with zsh like with (t)csh, you can also do ${PWD:t:s/trunk/latest/}.

Though bash also supports those csh history modifiers for history expansion, it doesn't support them for its parameter expansions.

Here with bash, use a temporary variable:

var=${PWD##*/} var=${var//trunk/latest}

Try this with bash:

[[ $PWD =~ .*/(.*) ]] && echo "${BASH_REMATCH[1]//trunk/latest}"

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or with one command:

[[ $PWD =~ .*/(.*) && ${BASH_REMATCH[1]//trunk/latest} =~ (.*) ]]

The result is in ${BASH_REMATCH[1]}