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    what is the name of this technique using the ? in the bracket expansion ${} ? I cannot wrap myn head around the meaning and behaviour of it. I suppose ? applies to th 1 in $1 ; but I'm left clueless, I'd gladly dig deeper this technique/syntax. Commented May 5, 2021 at 13:41
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    aka parameter expansion: gnu.org/software/bash/manual/html_node/… Commented Aug 9, 2021 at 20:44
  • How about an optional parameter? Commented Sep 16, 2022 at 19:39