1

In Zsh parameter expansion, I have:

"${test_var:-"${HOME}/test"}"

but here I want to check if ${HOME}/test is exist or not, if not exist then test_var expand to " " (one space string).

Is there an inline solution for this?

  • And if it exists, what happens ? – don_crissti Nov 27 '18 at 20:22
  • @don_crissti: If test_var is not set or null then expand to ${HOME}/test but if ${HOME}/test not exist then expand test_var to " ", if ${HOME}/test exists then expand test_var to ${HOME}/test as usual. – Tuyen Pham Nov 28 '18 at 2:24
2
echo ${test_var:-~/test(N)}

comes close. By adding a (N) (and here as we are in list context), that ~/test(N) becomes a glob, and because of that N glob qualifier, if there's no test directory entry in $HOME (~), then the glob expands to nothing.

That's different from what you're asking in that it expands to nothing at all, instead of a one space argument.

For that, you could still do it in to steps:

f=(~/test(N)); echo ${test_var:-${f:-' '}}

You could also use command substitution, though that's a bit cheating:

echo ${test_var:-"${$(printf %s ~/test(N)):-' '}"}

Or:

echo ${test_var:-"$((){<<<${1-' '}} ~/test(N))"}
  • How to put f=(~/test(N)); echo ${test_var:-${f:-' '}} into position of ~/test(N) in echo ${test_var:-~/test(N)}? – Tuyen Pham Dec 2 '18 at 16:08

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